The North Pole saw record high temperatures for February during 2018.
Record Temperature at North Pole
Reuters reported:
Temperatures may have soared as high as 35 degrees Fahrenheit (2 degrees Celsius) at the pole, according to the U.S. Global Forecast System model. While there are no direct measurements of temperature there, Zack Labe, a climate scientist working on his PhD at the University of California at Irvine, confirmed that several independent analyses showed “it was very close to freezing,” which is more than 50 degrees (30 degrees Celsius) above normal.
The warm intrusion penetrated right through the heart of the Central Arctic, Labe said. The temperature averaged for the entire region north of 80 degrees latitude spiked to its highest level ever recorded in February. The average temperature was more than 36 degrees (20 degrees Celsius) above normal. “No other warm intrusions were very close to this,” Labe said in an interview, describing a data set maintained by the Danish Meteorological Institute that dates back to 1958. “I was taken by surprise how expansive this warm intrusion was.”
Climate scientist Sidd Mukherjee added, “Yes. Even more scarily — the fast ice north of Greenland is gone. That was some of the oldest ice left. It hasn’t melted, just been blown away and drifted away with the currents.” (see “Talk about unprecedented“)
An article in Rolling Stone about climate migrations quotes Solomon Hsiang:
Hsiang has many good papers outAn article in Rolling Stone about climate migrations quotes Solomon Hsiang:
“Most people don’t realize how much climate affects everything, from their property values to how hard people work,” says Solomon Hsiang, a professor of public policy at the University of California, Berkeley, who led a recent study that predicts, as the climate warms, there will be “a large transfer of value northward and westward.” And the wealthy, who can afford to adapt, will benefit, while the poor, who will likely be left behind, will suffer. “If we continue on the current path,” Hsiang says, “our analysis suggests that climate change may result in the largest transfer of wealth from the poor to the rich in the country’s history.”
Dr. Mukherjee replied, “But for city officials in at-risk cities, homeowners like Brown are terrifying. “Once people start thinking about the long-term value of their homes and how they will be impacted by climate change, that changes the game completely,” a county attorney in Florida says. What happens to the value of a house in, for instance, Fort Lauderdale, when the cost of flood insurance triples? “When I think about the future of South Florida, it’s flood insurance that scares me the most,” Wayne Pathman, a prominent Miami lawyer and board member of Miami Beach’s chamber of commerce, tells me. Many officials fear a climate-driven exodus that pushes down property values, which in turn reduces property-tax revenues, which are central to funding city services like police and teachers, not to mention road repair and infrastructure maintenance, at precisely the moment when the city needs to spend more to adapt to climate change.
Flooding in downtown Miami after Hurricane Irma in September 2017. Kadir van Lohuizen/NOOR/Redux
It’s a downward spiral for real estate that’s very hard to reverse. “It’s just like the dynamic in the stock market,” says U.C. Berkeley’s Hsiang. “The longer you hold on, the more you have to lose.” And, in many cases, the regions of the country where climate-change denial is strongest, such as the Southeast, are exactly the regions where residents have the most to lose. “In many places, climate denial is going to turn out to have big economic consequences,” Hsiang says.
[Hsiang has many good papers out]
In a recent study by Matthias Mengel, Alexander Nauels, Joeri Rogelj & Carl-Friedrich Schleussner entitled “Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action” published in the Journal Nature, the authors contend — sea levels will rise between 0.7 and 1.2 meters (27-47 inches) in the next two centuries even if governments end the fossil fuel era as committed to under the Paris climate agreement.
THE ABSTRACT
Sea-level rise is a major consequence of climate change that will continue long after emissions of greenhouse gases have stopped. The 2015 Paris Agreement aims at reducing climate-related risks by reducing greenhouse gas emissions to net zero and limiting global-mean temperature increase. Here we quantify the effect of these constraints on global sea-level rise until 2300, including Antarctic ice-sheet instabilities. We estimate median sea-level rise between 0.7 and 1.2 m, if net-zero greenhouse gas emissions are sustained until 2300, varying with the pathway of emissions during this century. Temperature stabilization below 2 °C is insufficient to hold median sea-level rise until 2300 below 1.5 m. We find that each 5-year delay in near-term peaking of CO2 emissions increases median year 2300 sea-level rise estimates by ca. 0.2 m, and extreme sea-level rise estimates at the 95th percentile by up to 1 m. Our results underline the importance of near-term mitigation action for limiting long-term sea-level rise risks.
A 3-foot rise in sea level would put much of the United States’ East Coast, Florida and New Orleans underwater.
The report is an authoritative assessment of the science of climate change, with a focus on the United States. It represents the first of two volumes of the Fourth National Climate Assessment, mandated by the Global Change Research Act of 1990.
The report’s summary states:
Global annually averaged surface air temperature has increased by about 1.8°F (1.0°C) over the last 115 years (1901–2016). This period is now the warmest in the history of modern civilization. The last few years have also seen record-breaking, climate-related weather extremes, and the last three years have been the warmest years on record for the globe. These trends are expected to continue over climate timescales.This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.In addition to warming, many other aspects of global climate are changing, primarily in response to human activities. Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor.
For example, global average sea level has risen by about 7–8 inches since 1900, with almost half (about 3 inches) of that rise occurring since 1993. Human-caused climate change has made a substantial contribution to this rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years. Global sea level rise has already affected the United States; the incidence of daily tidal flooding is accelerating in more than 25 Atlantic and Gulf Coast cities.
Global average sea levels are expected to continue to rise—by at least several inches in the next 15 years and by 1–4 feet by 2100. A rise of as much as 8 feet by 2100 cannot be ruled out. Sea level rise will be higher than the global average on the East and Gulf Coasts of the United States.
Changes in the characteristics of extreme events are particularly important for human safety, infrastructure, agriculture, water quality and quantity, and natural ecosystems. Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase. The largest observed changes in the United States have occurred in the Northeast.
Heatwaves have become more frequent in the United States since the 1960s, while extreme cold temperatures and cold waves are less frequent. Recent record-setting hot years are projected to become common in the near future for the United States, as annual average temperatures continue to rise. Annual average temperature over the contiguous United States has increased by 1.8°F (1.0°C) for the period 1901–2016; over the next few decades (2021–2050), annual average temperatures are expected to rise by about 2.5°F for the United States, relative to the recent past (average from 1976–2005), under all plausible future climate scenarios.
The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s and is projected to further increase in those regions as the climate changes, with profound changes to regional ecosystems.
Annual trends toward earlier spring melt and reduced snowpack are already affecting water resources in the western United States and these trends are expected to continue. Under higher scenarios, and assuming no change to current water resources management, chronic, long-duration hydrological drought is increasingly possible before the end of this century.
The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases (especially carbon dioxide) emitted globally. Without major reductions in emissions, the increase in annual average global temperature relative to preindustrial times could reach 9°F (5°C) or more by the end of this century. With significant reductions in emissions, the increase in annual average global temperature could be limited to 3.6°F (2°C) or less.
The global atmospheric carbon dioxide (CO2) concentration has now passed 400 parts per million (ppm), a level that last occurred about 3 million years ago, when both global average temperature and sea level were significantly higher than today. Continued growth in CO2 emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens to hundreds of millions of years. There is broad consensus that the further and the faster the Earth system is pushed towards warming, the greater the risk of unanticipated changes and impacts, some of which are potentially large and irreversible.
The observed increase in carbon emissions over the past 15–20 years has been consistent with higher emissions pathways. In 2014 and 2015, emission growth rates slowed as economic growth became less carbon-intensive. Even if this slowing trend continues, however, it is not yet at a rate that would limit global average temperature change to well below 3.6°F (2°C) above preindustrial levels.
Introduction
New observations and new research have increased our understanding of past, current, and future climate change since the Third U.S. National Climate Assessment (NCA3) was published in May 2014. This Climate Science Special Report (CSSR) is designed to capture that new information and build on the existing body of science in order to summarize the current state of knowledge and provide the scientific foundation for the Fourth National Climate Assessment (NCA4).
Since NCA3, stronger evidence has emerged for continuing, rapid, human-caused warming of the global atmosphere and ocean. This report concludes that “it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.”
The last few years have also seen record-breaking, climate-related weather extremes, the three warmest years on record for the globe, and continued decline in arctic sea ice. These trends are expected to continue in the future over climate (multidecadal) timescales. Significant advances have also been made in our understanding of extreme weather events and how they relate to increasing global temperatures and associated climate changes. Since 1980, the cost of extreme events for the United States has exceeded $1.1 trillion; therefore, better understanding of the frequency and severity of these events in the context of a changing climate is warranted.
Periodically taking stock of the current state of knowledge about climate change and putting new weather extremes, changes in sea ice, increases in ocean temperatures, and ocean acidification into context ensures that rigorous, scientifically-based information is available to inform dialogue and decisions at every level. This climate science report serves as the climate science foundation of the NCA4 and is generally intended for those who have a technical background in climate science. In this Executive Summary, green boxes present highlights of the main report. These are followed by related points and selected figures providing more scientific details. The summary material on each topic presents the most salient points of chapter findings and therefore represents only a subset of the report’s content. For more details, the reader is referred to the individual chapters. This report discusses climate trends and findings at several scales: global, nationwide for the United States, and for ten specific U.S. regions (shown in Figure 1 in the Guide to the Report). A statement of scientific confidence also follows each point in the Executive Summary. The confidence scale is described in the Guide to the Report. At the end of the Executive Summary and in Chapter 1: Our Globally Changing Climate, there is also a summary box highlighting the most notable advances and topics since NCA3 and since the 2013 Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report.
Global and U.S. Temperatures Continue to Rise
Long-term temperature observations are among the most consistent and widespread evidence of a warming planet. Temperature (and, above all, its local averages and extremes) affects agricultural productivity, energy use, human health, water resources, infrastructure, natural ecosystems, and many other essential aspects of society and the natural environment. Recent data add to the weight of evidence for rapid global-scale warming, the dominance of human causes, and the expected continuation of increasing temperatures, including more record-setting extremes. (Ch. 1)
Changes in Observed and Projected Global Temperature
Global annual average temperature (as calculated from instrumental records over both land and oceans) has increased by more than 1.2°F (0.65°C) for the period 1986–2016 relative to 1901–1960; the linear regression change over the entire period from 1901–2016 is 1.8°F (1.0°C) (very high confidence; Fig. ES.1). Longer-term climate records over past centuries and millennia indicate that average temperatures in recent decades over much of the world have been much higher, and have risen faster during this time period than at any time in the past 1,700 years or more, the time period for which the global distribution of surface temperatures can be reconstructed (high confidence). (Ch. 1)
Figure 1
(left) Global annual average temperature has increased by more than 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960. Red bars show temperatures that were above the 1901–1960 average, and blue bars indicate temperatures below the average. (right) Surface temperature change (in °F) for the period 1986–2016 relative to 1901–1960. Gray indicates missing data. From Figures 1.2. and 1.3 in Chapter 1.
Many lines of evidence demonstrate that it is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century. Over the last century, there are no convincing alternative explanations supported by the extent of the observational evidence. Solar output changes and internal natural variability can only contribute marginally to the observed changes in climate over the last century, and there is no convincing evidence for natural cycles in the observational record that could explain the observed changes in climate. (Very high confidence) (Ch. 1)
Figure 2
The likely range of the human contribution to the global mean temperature increase over the period 1951–2010 is 1.1° to 1.4°F (0.6° to 0.8°C), and the central estimate of the observed warming of 1.2°F (0.65°C) lies within this range (high confidence). This translates to a likely human contribution of 92%–123% of the observed 1951–2010 change. The likely contributions of natural forcing and internal variability to global temperature change over that period are minor (high confidence). (Ch. 3; Fig. ES.2)
Natural variability, including El Niño events and other recurring patterns of ocean–atmosphere interactions, impact temperature and precipitation, especially regionally, over timescales of months to years. The global influence of natural variability, however, is limited to a small fraction of observed climate trends over decades. (Very high confidence) (Ch. 1)
Global climate is projected to continue to change over this century and beyond. The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse (heat-trapping) gases emitted globally and on the remaining uncertainty in the sensitivity of Earth’s climate to those emissions (very high confidence). With significant reductions in the emissions of greenhouse gases, the global annually averaged temperature rise could be limited to 3.6°F (2°C) or less. Without major reductions in these emissions, the increase in annual average global temperatures relative to pre-industrial times could reach 9°F (5°C) or more by the end of this century. (Ch.1; Fig ES.3)
If greenhouse gas concentrations were stabilized at their current level, existing concentrations would commit the world to at least an additional 1.1°F (0.6°C) of warming over this century relative to the last few decades (high confidence in continued warming, medium confidence in amount of warming. (Ch.4)
Figure 3
The two panels above show annual historical and a range of plausible future carbon emissions in units of gigatons of carbon (GtC) per year (left) and the historical observed and future temperature change that would result for a range of future scenarios relative to the 1901–1960 average, based on the central estimate (lines) and a range (shaded areas, two standard deviations) as simulated by the full suite of CMIP5 global climate models (right). By 2081–2100, the projected range in global mean temperature change is 1.1°–4.3°F under the even lower scenario (RCP2.6; 0.6°–2.4°C, green), 2.4°–5.9°F under the lower scenario (RCP4.5; 1.3°–3.3°C, blue), 3.0°–6.8°F under the mid-high scenario (RCP6.0; 1.6°–3.8°C, not shown) and 5.0°–10.2°F under the higher scenario (RCP8.5; 2.8°–5.7°C, orange). See the main report for more details on these scenarios and implications. Based on Figure 4.1 in Chapter 4.
Changes in Observed and Projected U.S. Temperature
Annual average temperature over the contiguous United States has increased by 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960 and by 1.8°F (1.0°C) based on a linear regression for the period 1901–2016 (very high confidence). Surface and satellite data are consistent in their depiction of rapid warming since 1979 (high confidence). Paleo-temperature evidence shows that recent decades are the warmest of the past 1,500 years (medium confidence). (Ch. 6)
Annual average temperature over the contiguous United States is projected to rise (very high confidence). Increases of about 2.5°F (1.4°C) are projected for the period 2021–2050 relative to the average from 1976–2005 in all RCP scenarios, implying recent record-setting years may be “common” in the next few decades (high confidence). Much larger rises are projected by late century (2071–2100): 2.8°–7.3°F (1.6°–4.1°C) in a lower scenario (RCP4.5) and 5.8°–11.9°F (3.2°–6.6°C) in a higher scenario (RCP8.5) (high confidence). (Ch. 6; Fig. ES.4)
In the United States, the urban heat island effect results in daytime temperatures 0.9°–7.2°F (0.5°–4.0°C) higher and nighttime temperatures 1.8°– 4.5°F (1.0°–2.5°C) higher in urban areas than in rural areas, with larger temperature differences in humid regions (primarily in the eastern United States) and in cities with larger and denser populations. The urban heat island effect will strengthen in the future as the structure and spatial extent as well as population density of urban areas change and grow (high confidence). (Ch. 10)
Figure 4
These maps show the projected changes in annual average temperatures for mid- and late-21st century for two future pathways. Changes are the differences between the average projected temperatures for mid-century (2036–2065; top), and late-century (2070-2099; bottom), and those observed for the near-present (1976–2005). See Figure 6.7 in Chapter 6 for more details.
Many Temperature and Precipitation Extremes Are Becoming More Common
Temperature and precipitation extremes can affect water quality and availability, agricultural productivity, human health, vital infrastructure, iconic ecosystems and species, and the likelihood of disasters. Some extremes have already become more frequent, intense, or of longer duration, and many extremes are expected to continue to increase or worsen, presenting substantial challenges for built, agricultural, and natural systems. Some storm types such as hurricanes, tornadoes, and winter storms are also exhibiting changes that have been linked to climate change, although the current state of the science does not yet permit detailed understanding.
Observed Changes in Extremes
Figure 5
The frequency of cold waves has decreased since the early 1900s, and the frequency of heat waves has increased since the mid-1960s (the Dust Bowl era of the 1930s remains the peak period for extreme heat in the United States). (Very high confidence). (Ch. 6)
The frequency and intensity of extreme heat and heavy precipitation events are increasing in most continental regions of the world (very high confidence). These trends are consistent with expected physical responses to a warming climate. Climate model studies are also consistent with these trends, although models tend to underestimate the observed trends, especially for the increase in extreme precipitation events (very high confidence for temperature, high confidence for extreme precipitation). (Ch. 1)
Figure 6
These maps show the percentage change in several metrics of extreme precipitation by NCA4 region, including (upper left) the maximum daily precipitation in consecutive 5-year periods; (upper right) the amount of precipitation falling in daily events that exceed the 99th percentile of all non-zero precipitation days (top 1% of all daily precipitation events); (lower left) the number of 2-day events with a precipitation total exceeding the largest 2-day amount that is expected to occur, on average, only once every 5 years, as calculated over 1901–2016; and (lower right) the number of 2-day events with a precipitation total exceeding the largest 2-day amount that is expected to occur, on average, only once every 5 years, as calculated over 1958–2016. The number in each black circle is the percent change over the entire period, either 1901–2016 or 1958–2016. Note that Alaska and Hawai‘i are not included in the 1901–2016 maps owing to a lack of observations in the earlier part of the 20th century. (Figure source: CICS-NC / NOAA NCEI). Based on Figure 7.4 in Chapter 7.
Recent droughts and associated heat waves have reached record intensity in some regions of the United States; however, by geographical scale and duration, the Dust Bowl era of the 1930s remains the benchmark drought and extreme heat event in the historical record. (Very high confidence) (Ch. 8)
Northern Hemisphere spring snow cover extent, North America maximum snow depth, snow water equivalent in the western United States, and extreme snowfall years in the southern and western United States have all declined, while extreme snowfall years in parts of the northern United States have increased. (Medium confidence). (Ch. 7)
There has been a trend toward earlier snowmelt and a decrease in snowstorm frequency on the southern margins of climatologically snowy areas (medium confidence). Winter storm tracks have shifted northward since 1950 over the Northern Hemisphere (medium confidence). Potential linkages between the frequency and intensity of severe winter storms in the United States and accelerated warming in the Arctic have been postulated, but they are complex, and, to some extent, contested, and confidence in the connection is currently low. (Ch. 9)
Tornado activity in the United States has become more variable, particularly over the 2000s, with a decrease in the number of days per year with tornadoes and an increase in the number of tornadoes on these days (medium confidence). Confidence in past trends for hail and severe thunderstorm winds, however, is low (Ch. 9)
Projected Changes in Extremes
The frequency and intensity of extreme high temperature events are virtually certain to increase in the future as global temperature increases (high confidence). Extreme precipitation events will very likely continue to increase in frequency and intensity throughout most of the world (high confidence). Observed and projected trends for some other types of extreme events, such as floods, droughts, and severe storms, have more variable regional characteristics. (Ch. 1)
Both extremely cold days and extremely warm days are expected to become warmer. Cold waves are predicted to become less intense while heat waves will become more intense. The number of days below freezing is projected to decline while the number above 90°F will rise. (Very high confidence) (Ch. 6)
The frequency and intensity of heavy precipitation events in the United States are projected to continue to increase over the 21st century (high confidence). There are, however, important regional and seasonal differences in projected changes in total precipitation: the northern United States, including Alaska, is projected to receive more precipitation in the winter and spring, and parts of the southwestern United States are projected to receive less precipitation in the winter and spring (medium confidence). (Ch. 7)
The frequency and severity of landfalling “atmospheric rivers” on the U.S. West Coast (narrow streams of moisture that account for 30%–40% of the typical snowpack and annual precipitation in the region and are associated with severe flooding events) will increase as a result of increasing evaporation and resulting higher atmospheric water vapor that occurs with increasing temperature. (Medium confidence) (Ch. 9)
Projections indicate large declines in snowpack in the western United States and shifts to more precipitation falling as rain than snow in the cold season in many parts of the central and eastern United States (high confidence). (Ch. 7)
Substantial reductions in western U.S. winter and spring snowpack are projected as the climate warms. Earlier spring melt and reduced snow water equivalent have been formally attributed to human-induced warming (high confidence) and will very likely be exacerbated as the climate continues to warm (very high confidence). Under higher scenarios, and assuming no change to current water resources management, chronic, long-duration hydrological drought is increasingly possible by the end of this century (very high confidence). (Ch. 8)
The human effect on recent major U.S. droughts is complicated. Little evidence is found for a human influence on observed precipitation deficits, but much evidence is found for a human influence on surface soil moisture deficits due to increased evapotranspiration caused by higher temperatures. (High confidence) (Ch. 8)
The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s (high confidence) and is projected to further increase in those regions as the climate warms, with profound changes to certain ecosystems (medium confidence). (Ch. 8)
Both physics and numerical modeling simulations generally indicate an increase in tropical cyclone intensity in a warmer world, and the models generally show an increase in the number of very intense tropical cyclones. For Atlantic and eastern North Pacific hurricanes and western North Pacific typhoons, increases are projected in precipitation rates (high confidence) and intensity (medium confidence). The frequency of the most intense of these storms is projected to increase in the Atlantic and western North Pacific (low confidence) and in the eastern North Pacific (medium confidence). (Ch. 9)
Oceans Are Rising, Warming, and Becoming More Acidic
Oceans occupy two-thirds of the planet’s surface and host unique ecosystems and species, including those important for global commercial and subsistence fishing. Understanding climate impacts on the ocean and the ocean’s feedbacks to the climate system is critical for a comprehensive understanding of current and future changes in climate.
Global Ocean Heat
Ocean heat content has increased at all depths since the 1960s and surface waters have warmed by about 1.3° ± 0.1°F (0.7° ± 0.08°C) per century globally since 1900 to 2016. Under higher scenarios, a global increase in average sea surface temperature of 4.9° ± 1.3°F (2.7° ± 0.7°C) is projected by 2100. (Very high confidence). (Ch. 13)
Global and Regional Sea Level Rise
Human-caused climate change has made a substantial contribution to GMSL rise since 1900 (high confidence), contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years (medium confidence). (Ch. 12; Fig. ES.8)
Relative to the year 2000, GMSL is very likely to rise by 0.3–0.6 feet (9–18 cm) by 2030, 0.5–1.2 feet (15–38 cm) by 2050, and 1.0–4.3 feet (30–130 cm) by 2100 (very high confidence in lower bounds; medium confidence in upper bounds for 2030 and 2050; low confidence in upper bounds for 2100). Future emissions pathways have little effect on projected GMSL rise in the first half of the century, but significantly affect projections for the second half of the century (high confidence). (Ch. 12)
Figure 8
The top panel shows observed and reconstructed mean sea level for the last 2,500 years. The bottom panel shows projected mean sea level for six future scenarios. The six scenarios—spanning a range designed to inform a variety of decision makers—extend from a low scenario, consistent with continuation of the rate of sea level rise over the last quarter century, to an extreme scenario, assuming rapid mass loss from the Antarctic ice sheet. Note that the range on the vertical axis in the bottom graph is approximately ten times greater than in the top graph. Based on Figure 12.2 and 12.4 in Chapter 12. See the main report for more details.
Emerging science regarding Antarctic ice sheet stability suggests that, for higher scenarios, a GMSL rise exceeding 8 feet (2.4 m) by 2100 is physically possible, although the probability of such an extreme outcome cannot currently be assessed. Regardless of emission pathway, it is extremely likely that GMSL rise will continue beyond 2100 (high confidence). (Ch. 12)
Relative sea level rise in this century will vary along U.S. coastlines due, in part, to changes in Earth’s gravitational field and rotation from melting of land ice, changes in ocean circulation, and vertical land motion (very high confidence). For almost all future GMSL rise scenarios, relative sea level rise is likely to be greater than the global average in the U.S. Northeast and the western Gulf of Mexico. In intermediate and low GMSL rise scenarios, relative sea level rise is likely to be less than the global average in much of the Pacific Northwest and Alaska. For high GMSL rise scenarios, relative sea level rise is likely to be higher than the global average along all U.S. coastlines outside Alaska. Almost all U.S. coastlines experience more than global mean sea level rise in response to Antarctic ice loss, and thus would be particularly affected under extreme GMSL rise scenarios involving substantial Antarctic mass loss (high confidence). (Ch. 12)
Coastal Flooding
Figure 9
As sea levels have risen, the number of tidal floods each year that cause minor impacts (also called “nuisance floods”) have increased 5- to 10-fold since the 1960s in several U.S. coastal cities (very high confidence). Rates of increase are accelerating in over 25 Atlantic and Gulf Coast cities (very high confidence). Tidal flooding will continue increasing in depth, frequency, and extent this century (very high confidence). (Ch. 12)
Assuming storm characteristics do not change, sea level rise will increase the frequency and extent of extreme flooding associated with coastal storms, such as hurricanes and nor’easters (very high confidence). A projected increase in the intensity of hurricanes in the North Atlantic (medium confidence) could increase the probability of extreme flooding along most of the U.S. Atlantic and Gulf Coast states beyond what would be projected based solely on relative sea level rise. However, there is low confidence in the projected increase in frequency of intense Atlantic hurricanes, and the associated flood risk amplification, and flood effects could be offset or amplified by such factors, such as changes in overall storm frequency or tracks. (Ch.12; Fig. ES. 9)
Global Ocean Circulation
The potential slowing of the Atlantic meridional overturning circulation (AMOC; of which the Gulf Stream is one component)—as a result of increasing ocean heat content and freshwater-driven buoyancy changes—could have dramatic climate feedbacks as the ocean absorbs less heat and CO2 from the atmosphere. This slowing would also affect the climates of North America and Europe. Any slowing documented to date cannot be directly tied to human-caused forcing, primarily due to lack of adequate observational data and to challenges in modeling ocean circulation changes. Under a higher scenario (RCP8.5), models show that the AMOC weakens over the 21st century (low confidence). (Ch. 13)
Global and Regional Ocean Acidification
Higher-latitude systems typically have a lower buffering capacity against changing acidity, exhibiting seasonally corrosive conditions sooner than low-latitude systems. The rate of acidification is unparalleled in at least the past 66 million years (medium confidence). Under the higher scenario (RCP8.5), the global average surface ocean acidity is projected to increase by 100% to 150% (high confidence). (Ch. 13)
Acidification is regionally greater than the global average along U.S. coastal systems as a result of upwelling (e.g., in the Pacific Northwest) (high confidence), changes in freshwater inputs (e.g., in the Gulf of Maine) (medium confidence), and nutrient input (e.g., in urbanized estuaries) (high confidence). (Ch. 13)
Ocean Oxygen
Increasing sea surface temperatures, rising sea levels, and changing patterns of precipitation, winds, nutrients, and ocean circulation are contributing to overall declining oxygen concentrations at intermediate depths in various ocean locations and in many coastal areas. Over the last half century, major oxygen losses have occurred in inland seas, estuaries, and in the coastal and open ocean (high confidence). Ocean oxygen levels are projected to decrease by as much as 3.5% under the higher scenario (RCP8.5) by 2100 relative to preindustrial values (high confidence). (Ch. 13)
Climate Change in Alaska and across the Arctic Continues to Outpace Global Climate Change
Residents of Alaska are on the front lines of climate change. Crumbling buildings, roads, and bridges and eroding shorelines are commonplace. Accelerated melting of multiyear sea ice cover, mass loss from the Greenland Ice Sheet, reduced snow cover, and permafrost thawing are stark examples of the rapid changes occurring in the Arctic. Furthermore, because elements of the climate system are interconnected (see Box ES.1), changes in the Arctic influence climate conditions outside the Arctic.
Arctic Temperature Increases
Rising Alaskan permafrost temperatures are causing permafrost to thaw and become more discontinuous; this process releases additional carbon dioxide and methane resulting in additional warming (high confidence). The overall magnitude of the permafrost-carbon feedback is uncertain (Ch. 2); however, it is clear that these emissions have the potential to compromise the ability to limit global temperature increases. (Ch. 11)
Atmospheric circulation patterns connect the climates of the Arctic and the contiguous United States. Evidenced by recent record warm temperatures in the Arctic and emerging science, the midlatitude circulation has influenced observed arctic temperatures and sea ice (high confidence). However, confidence is low regarding whether or by what mechanisms observed arctic warming may have influenced the midlatitude circulation and weather patterns over the continental United States. The influence of arctic changes on U.S. weather over the coming decades remains an open question with the potential for significant impact. (Ch. 11)
Arctic Land Ice Loss
Arctic land ice loss observed in the last three decades continues, in some cases accelerating (very high confidence). It is virtually certain that Alaska glaciers have lost mass over the last 50 years, with each year since 1984 showing an annual average ice mass less than the previous year. Over the satellite record, average ice mass loss from Greenland was −269 Gt per year between April 2002 and April 2016, accelerating in recent years (high confidence). (Ch. 11)
Arctic Sea Ice Loss
Arctic sea ice loss is expected to continue through the 21st century, very likely resulting in nearly sea ice-free late summers by the 2040s (very high confidence). (Ch. 11)
It is very likely that human activities have contributed to observed arctic surface temperature warming, sea ice loss, glacier mass loss, and northern hemisphere snow extent decline (high confidence). (Ch. 11)
Figure 10
September sea ice extent and age shown for (top) 1984 and (middle) 2016, illustrating significant reductions in sea ice extent and age (thickness). The bar graph in the lower right of each panel illustrates the sea ice area (unit: million km2) covered within each age category (> 1 year), and the green bars represent the maximum extent for each age range during the record. The year 1984 is representative of September sea ice characteristics during the 1980s. The years 1984 and 2016 are selected as endpoints in the time series; a movie of the complete time series is available at http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4489. (bottom) The satellite-era arctic sea ice areal extent trend from 1979 to 2016 for September (unit: million mi2). From Figure 11.1 in Chapter 11.
Limiting Globally Averaged Warming to 2°C (3.6°F) Will Require Major Reductions in Emissions
Human activities are now the dominant cause of the observed trends in climate. For that reason, future climate projections are based on scenarios of how human activities will continue to affect the climate over the remainder of this century and beyond (see Sidebar: Scenarios Used in this Assessment). There remains significant uncertainty about future emissions due to changing economic, political, and demographic factors. For that reason, this report quantifies possible climate changes for a broad set of plausible future scenarios through the end of the century. (Ch. 2, 4, 10, 14)
Global mean atmospheric carbon dioxide (CO2) concentration has now passed 400 ppm, a level that last occurred about 3 million years ago, when global average temperature and sea level were significantly higher than today (high confidence). Continued growth in CO2 emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens of millions of years (medium confidence). The present-day emissions rate of nearly 10 GtC per year suggests that there is no climate analog for this century any time in at least the last 50 million years (medium confidence). (Ch. 4)
Warming and associated climate effects from CO2 emissions persist for decades to millennia. In the near-term, changes in climate are determined by past and present greenhouse gas emissions modified by natural variability. Reducing net emissions of CO2 is necessary to limit near-term climate change and long-term warming. Other greenhouse gases (e.g., methane) and black carbon aerosols exert stronger warming effects than CO2 on a per ton basis, but they do not persist as long in the atmosphere (Ch. 2); therefore, mitigation of non-CO2 species contributes substantially to near-term cooling benefits but cannot be relied upon for ultimate stabilization goals. (Very high confidence) (Ch. 14)
Stabilizing global mean temperature to less than 3.6°F (2°C) above preindustrial levels requires substantial reductions in net global CO2 emissions prior to 2040 relative to present-day values before 2040 and likely requires net emissions to become zero or possibly negative later in the century. After accounting for the temperature effects of non-CO2 species, cumulative global CO2 emissions must stay below about 800 GtC in order to provide a two-thirds likelihood of preventing 3.6°F (2°C) of warming. Given estimated cumulative emissions since 1870, no more than approximately 230 GtC may be emitted in the future in order to remain under this temperature limit. Assuming global emissions are equal to or greater than those consistent with the RCP4.5 scenario, this cumulative carbon threshold would be exceeded in approximately two decades. (Ch. 14)
Achieving global greenhouse gas emissions reductions before 2030 consistent with targets and actions announced by governments in the lead up to the 2015 Paris climate conference would hold open the possibility of meeting the long-term temperature goal of limiting global warming to 3.6°F (2°C) above preindustrial levels, whereas there would be virtually no chance if net global emissions followed a pathway well above those implied by country announcements. Actions in the announcements are, by themselves, insufficient to meet a 3.6°F (2°C) goal; the likelihood of achieving that depends strongly on the magnitude of global emissions reductions after 2030. (High confidence) (Ch. 14)
Climate intervention or geoengineering strategies such as solar radiation management are measures that attempt to limit or reduce global temperature increases. Further assessments of the technical feasibilities, costs, risks, co-benefits, and governance challenges of climate intervention or geoengineering strategies, which are as yet unproven at scale, are a necessary step before judgments about the benefits and risks of these approaches can be made with high confidence. (High confidence) (Ch. 14)
In recent decades, land-use and land-cover changes have turned the terrestrial biosphere (soil and plants) into a net “sink” for carbon (drawing down carbon from the atmosphere), and this sink has steadily increased since 1980 (high confidence). Because of the uncertainty in the trajectory of land cover, the possibility of the land becoming a net carbon source cannot be excluded (very high confidence). (Ch. 10)
There is a Significant Possibility for Unanticipated Changes
Humanity’s effect on the Earth system, through the large-scale combustion of fossil fuels and widespread deforestation and the resulting release of carbon dioxide (CO2) into the atmosphere, as well as through emissions of other greenhouse gases and radiatively active substances from human activities, is unprecedented. There is significant potential for humanity’s effect on the planet to result in unanticipated surprises and a broad consensus that the further and faster the Earth system is pushed towards warming, the greater the risk of such surprises.
There are at least two types of potential surprises: compound events, where multiple extreme climate events occur simultaneously or sequentially (creating greater overall impact), and critical threshold or tipping pointevents, where some threshold is crossed in the climate system (that leads to large impacts). The probability of such surprises—some of which may be abrupt and/or irreversible—as well as other more predictable but difficult-to-manage impacts, increases as the influence of human activities on the climate system increases. (Ch. 15)
Positive feedbacks (self-reinforcing cycles) within the climate system have the potential to accelerate human-induced climate change and even shift the Earth’s climate system, in part or in whole, into new states that are very different from those experienced in the recent past (for example, ones with greatly diminished ice sheets or different large-scale patterns of atmosphere or ocean circulation). Some feedbacks and potential state shifts can be modeled and quantified; others can be modeled or identified but not quantified; and some are probably still unknown. (Very high confidence in the potential for state shifts and in the incompleteness of knowledge about feedbacks and potential state shifts). (Ch. 15)
The physical and socioeconomic impacts of compound extreme events (such as simultaneous heat and drought, wildfires associated with hot and dry conditions, or flooding associated with high precipitation on top of snow or waterlogged ground) can be greater than the sum of the parts (very high confidence). Few analyses consider the spatial or temporal correlation between extreme events. (Ch. 15)
While climate models incorporate important climate processes that can be well quantified, they do not include all of the processes that can contribute to feedbacks (Ch. 2), compound extreme events, and abrupt and/or irreversible changes. For this reason, future changes outside the range projected by climate models cannot be ruled out (very high confidence). Moreover, the systematic tendency of climate models to underestimate temperature change during warm paleoclimates suggests that climate models are more likely to underestimate than to overestimate the amount of long-term future change (medium confidence). (Ch. 15)
The most likely force to cause a change in climate change is money. New York City is filing a law suit against five major oil companies (BP, Chevron, ConocoPhillips, Exxon Mobil and Royal Dutch Shell), claiming they have contributed to global warming. Mayor Bill de Blasio said the city will seek billions of dollars in the lawsuit to recoup money spent by the city for resiliency efforts related to global warming.
Bomb Cyclone Storm on January 4, 2018 off the Northeastern Shore
“‘Bomb cyclone’ blasting East Coast before polar vortex uncorks tremendous cold late this week. The most severe winter weather yet will assault the area late this week.” — washingtonpost.com (January 3, 2018)
The bomb cyclone blizzard was a 1,000 mile wide Nor’easter classified as a “bomb cyclone” because of its sharp drop in atmospheric pressure. “Bombogenesis, a popular term used by meteorologists, occurs when a midlatitude cyclone rapidly intensifies, dropping at least 24 millibars over 24 hours,” said NOAA.
“We are not saying that the Earth’s temperature is just going to rise. In general, as energy is added to a system, the fluctuations in the system increase. So, we expect more storms, more droughts, more wildfires, more floods, more fluctuations of all kinds. What we are saying is that weather conditions will become more volatile due to the impact of humans,” said Sidd Mukherjee and Daniel Brouse (2004)
“What use to be a once-in-a-hundred year event is now an annual event.” (2017)
“I think the public and many policymakers don’t really take those 100-year forecasts very seriously,” said Myles Allen, an Oxford scientist who is now one of the world’s leading experts in attribution science. “They are much more seriously interested in the question of what is happening now and why—which boils down to attribution.”
It use to be that scientists were reluctant to relate any single weather event to climate change; however, that has changed.
NOAA now issues a report for extreme weather events, “This report provides information on direct economic losses, deaths, and other impacts for numerous weather and climate disasters including tropical cyclones, floods, droughts and heat waves, severe storms (e.g., tornadoes, hail, and straight-line winds), wildfires, crop freeze events, and winter storms.”
The Bulletin of the American Meteorological Society now issues a special report each year assessing the impact of climate change on the previous year’s extreme events.
Scientific American reported, Myles Allen had hinted about “litigation two years before Hurricane Katrina occurred. In his Nature commentary, he mused about the possibility of massive class-action lawsuits—carrying the potential for “up to six billion plaintiffs” around the world—attempting to hold greenhouse gas emitters liable for damages.
Attribution studies could help to apportion the blame, he noted. For instance, he wrote, “If, at a given confidence level, past greenhouse-gas emissions have increased the risk of a flood tenfold, and that flood occurs, then we can attribute, at that confidence level, 90% of any damage to those past emissions.”
About 2017, NPR reported, “This year will go down in history for its extreme weather. Researchers have now definitively attributed three major extreme weather events to climate change.”
LINDA WERTHEIMER, HOST:
If you’re listening to this program from the Midwest or East Coast, well, I hope you’re nice and warm inside your house or car. President Trump took note of the frigid temperatures in the East this holiday season with this tweet – perhaps we could use a little bit of that good, old global warming.
Climate scientists note that while parts of the U.S. are much colder than average now, the world as a whole this week is warmer than the average over recent decades. One thing climate scientists have long been reluctant to say is that specific extreme weather events are the result of climate change. But NPR’s Christopher Joyce says a little-noticed study this past year did prove a link.
CHRISTOPHER JOYCE, BYLINE: This was this – a study that determined that, yes, looking at events in 2016, 27 of them – they found three that were so off the charts that they had to be the result of what we have done to the planet. They’re just beyond what is expected to be a natural event.
WERTHEIMER: What are they? What are the three events?
JOYCE: Well, one was the incredible heat that we experienced – the average temperature around the globe in 2016. It was 1.7 degrees Fahrenheit above the average in the 20th century. And that is just enormous. The second one – extreme heat waves in Asia, especially India and Pakistan. Hundreds of people died. The temperatures were just beyond belief. And the third one – one not noticed that much – but something called the blob, which was a section of water in the Bering Sea off the coast of Alaska that was just unusually warm – again, so warm that it’s just beyond what could be modeled as being – as happening in a natural world.
WERTHEIMER: But still, how do they know that this was not just weird weather – certainly, extreme, unexpected, unusual?
JOYCE: You know, again, I have to use the word model, which people are afraid of. But they’re computer models. And what you basically do is you recreate the world as it was before the Industrial Revolution and certainly before the mid-20th century when we started warming it up. And you put in all of the atmosphere. You put in the oceans, the circulation, the temperature. And you sort of create this world before we changed it. And then you create another model of the world we’re in. And you take these events, and you put them in that model of what the world used to be like. And you can tell that they couldn’t have been created by the forces that were at work before we warmed the planet.
WERTHEIMER: So those three things could not have happened absent global warming.
JOYCE: Yeah. I talked to one of the scientists who did the work – who compiled the work – Stephanie Herring of the National Oceanic and Atmospheric Administration. And this is how she put it.
(SOUNDBITE OF ARCHIVED RECORDING)
STEPHANIE HERRING: Not even one in a million. They cannot replicate them in a world without climate change is what the scientists are saying. It’s a big result, yes. It’s – again, you know, we’ve been doing this for six years, 131 papers. This is our first time seeing this.
The Lancet Commission published a report on October 19, 2017 that outlined the results of pollution and health. The report concluded that 9 million people suffered premature deaths due to pollution in 2015.
“Pollution is the largest environmental cause of disease and premature death in the world today. Diseases caused by pollution were responsible for an estimated 9 million premature deaths in 2015—16% of all deaths worldwide—three times more deaths than from AIDS, tuberculosis, and malaria combined and 15 times more than from all wars and other forms of violence. In the most severely affected countries, pollution-related disease is responsible for more than one death in four,” the report states.
Air pollution is the leading cause of death followed by water pollution. The financial cost from pollution-related death, sickness and welfare costs about $4.6 trillion in annual losses.
The report highlights:
Air pollution was linked to 6.5 million premature deaths;
Water pollution was linked to 1.8 million premature deaths;
Workplace pollution was linked to 1 million premature deaths;
Premature deaths resulting from pollution-related diseases like heart disease and cancer outnumbered AIDS, tuberculosis, and malaria combined 3 to 1;
About 92% of all premature deaths linked to pollution occur in low and middle-income countries.
Up to one in four deaths can be attributed to pollution in countries like China, India, Pakistan, or Bangladesh.
In absolute numbers, China (1.8 million) and India (2.5 million) had the most pollution-related deaths for the year 2015.
The United States, home to the world’s biggest economy, saw 155,000 premature deaths linked to pollution in 2015.
Q: How do you make gold and platinum?
A: Collide two neutron stars
“It’s so beautiful. It’s so beautiful it makes me want to cry. It’s the fulfillment of dozens, hundreds, thousands of people’s efforts, but it’s also the fulfillment of an idea suddenly becoming real,” said Peter Saulson of Syracuse University.
Not only does a collision of neutron stars create heavy metals, it also causes a wrinkle in space-time. Gravitational waves had been an Albert Einstein theory until 2015. Since then, there have been three recordings of gravitational waves; however, they were all colliding black holes. This was the first recording of gravitational waves in light.
The observation was made by LIGO:
Laser Interferometer Gravitational-Wave Observatory
Supported by the National Science Foundation
Operated by Caltech and MIT
Gravitational waves are ripples in the curvature of spacetime that are generated in certain gravitational interactions and propagate as waves outward from their source at the speed of light. The possibility of gravitational waves was discussed in 1893 by Oliver Heaviside using the analogy between the inverse-square law in gravitation and electricity. In 1905 Henri Poincaré first proposed gravitational waves (ondes gravifiques) emanating from a body and propagating at the speed of light as being required by the Lorentz transformations. Predicted in 1916 by Albert Einstein on the basis of his theory of general relativity, gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Newton’s law of universal gravitation, part of classical mechanics, does not provide for the existence of gravitational waves, since that law is predicated on the assumption that physical interactions propagate at infinite speed—showing one of the ways that the methods of classical physics is unable to explain phenomena associated with relativity.
GW170817 Press Release
LIGO and Virgo make first detection of gravitational waves produced by colliding neutron stars
Discovery marks first cosmic event observed in both gravitational waves and light.
Watch the recording of a press conference announcing the discovery, at the National Press Club in Washington, DC:
Watch the recording of a seminar at Caltech titled “Seeing and Hearing the Cataclysmic Universe” following the announcement:
For the first time, scientists have directly detected gravitational waves — ripples in space-time — in addition to light from the spectacular collision of two neutron stars. This marks the first time that a cosmic event has been viewed in both gravitational waves and light.
The discovery was made using the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO); the Europe-based Virgo detector; and some 70 ground- and space-based observatories.
Neutron stars are the smallest, densest stars known to exist and are formed when massive stars explode in supernovas. As these neutron stars spiraled together, they emitted gravitational waves that were detectable for about 100 seconds; when they collided, a flash of light in the form of gamma rays was emitted and seen on Earth about two seconds after the gravitational waves. In the days and weeks following the smashup, other forms of light, or electromagnetic radiation — including X-ray, ultraviolet, optical, infrared, and radio waves — were detected.
GW170817: A Global Astronomy Event
The observations have given astronomers an unprecedented opportunity to probe a collision of two neutron stars. For example, observations made by the U.S. Gemini Observatory, the European Very Large Telescope, and the Hubble Space Telescope reveal signatures of recently synthesized material, including gold and platinum, solving a decades-long mystery of where about half of all elements heavier than iron are produced.
The LIGO-Virgo results are published today in the journal Physical Review Letters; additional papers from the LIGO and Virgo collaborations and the astronomical community have been either submitted or accepted for publication in various journals.
“It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the universe,” says France A. Córdova, director of the National Science Foundation (NSF), which funds LIGO. “This discovery realizes a long-standing goal many of us have had, that is, to simultaneously observe rare cosmic events using both traditional as well as gravitational-wave observatories. Only through NSF’s four-decade investment in gravitational-wave observatories, coupled with telescopes that observe from radio to gamma-ray wavelengths, are we able to expand our opportunities to detect new cosmic phenomena and piece together a fresh narrative of the physics of stars in their death throes.”
A stellar sign
The gravitational signal, named GW170817, was first detected on Aug. 17 at 8:41 a.m. Eastern Daylight Time; the detection was made by the two identical LIGO detectors, located in Hanford, Washington, and Livingston, Louisiana. The information provided by the third detector, Virgo, situated near Pisa, Italy, enabled an improvement in localizing the cosmic event. At the time, LIGO was nearing the end of its second observing run since being upgraded in a program called Advanced LIGO, while Virgo had begun its first run after recently completing an upgrade known as Advanced Virgo.
Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana— Virgo in Italy and GEO600 in Germany.
The NSF-funded LIGO observatories were conceived, constructed, and operated by Caltech and MIT. Virgo is funded by the Istituto Nazionale di Fisica Nucleare (INFN) in Italy and the Centre National de la Recherche Scientifique (CNRS) in France, and operated by the European Gravitational Observatory. Some 1,500 scientists in the LIGO Scientific Collaboration and the Virgo Collaboration work together to operate the detectors and to process and understand the gravitational-wave data they capture.
Each observatory consists of two long tunnels arranged in an L shape, at the joint of which a laser beam is split in two. Light is sent down the length of each tunnel, then reflected back in the direction it came from by a suspended mirror. In the absence of gravitational waves, the laser light in each tunnel should return to the location where the beams were split at precisely the same time. If a gravitational wave passes through the observatory, it will alter each laser beam’s arrival time, creating an almost imperceptible change in the observatory’s output signal.
On Aug. 17, LIGO’s real-time data analysis software caught a strong signal of gravitational waves from space in one of the two LIGO detectors. At nearly the same time, the Gamma-ray Burst Monitor on NASA’s Fermi space telescope had detected a burst of gamma rays. LIGO-Virgo analysis software put the two signals together and saw it was highly unlikely to be a chance coincidence, and another automated LIGO analysis indicated that there was a coincident gravitational wave signal in the other LIGO detector. Rapid gravitational-wave detection by the LIGO-Virgo team, coupled with Fermi’s gamma-ray detection, enabled the launch of follow-up by telescopes around the world.
The LIGO data indicated that two astrophysical objects located at the relatively close distance of about 130 million light-years from Earth had been spiraling in toward each other. It appeared that the objects were not as massive as binary black holes — objects that LIGO and Virgo have previously detected. Instead, the inspiraling objects were estimated to be in a range from around 1.1 to 1.6 times the mass of the sun, in the mass range of neutron stars. A neutron star is about 20 kilometers, or 12 miles, in diameter and is so dense that a teaspoon of neutron star material has a mass of about a billion tons.
While binary black holes produce “chirps” lasting a fraction of a second in the LIGO detector’s sensitive band, the Aug. 17 chirp lasted approximately 100 seconds and was seen through the entire frequency range of LIGO — about the same range as common musical instruments. Scientists could identify the chirp source as objects that were much less massive than the black holes seen to date.
LIGO’s data shows the “chirp” sound produced as the two neutron stars inspiral.
“It immediately appeared to us the source was likely to be neutron stars, the other coveted source we were hoping to see — and promising the world we would see,” says David Shoemaker, spokesperson for the LIGO Scientific Collaboration and senior research scientist in MIT’s Kavli Institute for Astrophysics and Space Research. “From informing detailed models of the inner workings of neutron stars and the emissions they produce, to more fundamental physics such as general relativity, this event is just so rich. It is a gift that will keep on giving.”
“Our background analysis showed an event of this strength happens less than once in 80,000 years by random coincidence, so we recognized this right away as a very confident detection and a remarkably nearby source,” adds Laura Cadonati, professor of physics at Georgia Tech and deputy spokesperson for the LIGO Scientific Collaboration. “This detection has genuinely opened the doors to a new way of doing astrophysics. I expect it will be remembered as one of the most studied astrophysical events in history.”
Theorists have predicted that when neutron stars collide, they should give off gravitational waves and gamma rays, along with powerful jets that emit light across the electromagnetic spectrum. The gamma-ray burst detected by Fermi, and soon thereafter confirmed by the European Space Agency’s gamma-ray observatory INTEGRAL, is what’s called a short gamma-ray burst; the new observations confirm that at least some short gamma-ray bursts are generated by the merging of neutron stars — something that was only theorized before.
“For decades we’ve suspected short gamma-ray bursts were powered by neutron star mergers,” says Fermi Project Scientist Julie McEnery of NASA’s Goddard Space Flight Center. “Now, with the incredible data from LIGO and Virgo for this event, we have the answer. The gravitational waves tell us that the merging objects had masses consistent with neutron stars, and the flash of gamma rays tells us that the objects are unlikely to be black holes, since a collision of black holes is not expected to give off light.”
But while one mystery appears to be solved, new mysteries have emerged. The observed short gamma-ray burst was one of the closest to Earth seen so far, yet it was surprisingly weak for its distance. Scientists are beginning to propose models for why this might be, McEnery says, adding that new insights are likely to arise for years to come.
A patch in the sky
Though the LIGO detectors first picked up the gravitational wave in the United States, Virgo, in Italy, played a key role in the story. Due to its orientation with respect to the source at the time of detection, Virgo recovered a small signal; combined with the signal sizes and timing in the LIGO detectors, this allowed scientists to precisely triangulate the position in the sky. After performing a thorough vetting to make sure the signals were not an artifact of instrumentation, scientists concluded that a gravitational wave came from a relatively small patch in the southern sky.
Virgo Helps Localize Gravitational-Wave Signals
“This event has the most precise sky localization of all detected gravitational waves so far,” says Jo van den Brand of Nikhef (the Dutch National Institute for Subatomic Physics) and VU University Amsterdam, who is the spokesperson for the Virgo collaboration. “This record precision enabled astronomers to perform follow-up observations that led to a plethora of breathtaking results.”
“This result is a great example of the effectiveness of teamwork, of the importance of coordinating, and of the value of scientific collaboration,” adds EGO Director Federico Ferrini. “We are delighted to have played our relevant part in this extraordinary scientific challenge: Without Virgo, it would have been very difficult to locate the source of the gravitational wave.
Fermi was able to provide a localization that was later confirmed and greatly refined with the coordinates provided by the combined LIGO-Virgo detection. With these coordinates, a handful of observatories around the world were able, hours later, to start searching the region of the sky where the signal was thought to originate. A new point of light, resembling a new star, was first found by optical telescopes. Ultimately, about 70 observatories on the ground and in space observed the event at their representative wavelengths.
“This detection opens the window of a long-awaited ‘multi-messenger’ astronomy,” says Caltech’s David H. Reitze, executive director of the LIGO Laboratory. “It’s the first time that we’ve observed a cataclysmic astrophysical event in both gravitational waves and electromagnetic waves — our cosmic messengers. Gravitational-wave astronomy offers new opportunities to understand the properties of neutron stars in ways that just can’t be achieved with electromagnetic astronomy alone.”
A fireball and an afterglow
Each electromagnetic observatory will be releasing its own detailed observations of the astrophysical event. In the meantime, a general picture is emerging among all observatories involved that further confirms that the initial gravitational-wave signal indeed came from a pair of inspiraling neutron stars.
Approximately 130 million years ago, the two neutron stars were in their final moments of orbiting each other, separated only by about 300 kilometers, or 200 miles, and gathering speed while closing the distance between them. As the stars spiraled faster and closer together, they stretched and distorted the surrounding space-time, giving off energy in the form of powerful gravitational waves, before smashing into each other.
Neutron Star Merger Seen in Gravity and Matter
At the moment of collision, the bulk of the two neutron stars merged into one ultradense object, emitting a “fireball” of gamma rays. The initial gamma-ray measurements, combined with the gravitational-wave detection, also provide confirmation for Einstein’s general theory of relativity, which predicts that gravitational waves should travel at the speed of light.
Theorists have predicted that what follows the initial fireball is a “kilonova” — a phenomenon by which the material that is left over from the neutron star collision, which glows with light, is blown out of the immediate region and far out into space. The new light-based observations show that heavy elements, such as lead and gold, are created in these collisions and subsequently distributed throughout the universe.
In the weeks and months ahead, telescopes around the world will continue to observe the afterglow of the neutron star merger and gather further evidence about various stages of the merger, its interaction with its surroundings, and the processes that produce the heaviest elements in the universe.
“When we were first planning LIGO back in the late 1980s, we knew that we would ultimately need an international network of gravitational-wave observatories, including Europe, to help localize the gravitational-wave sources so that light-based telescopes can follow up and study the glow of events like this neutron star merger,” says Caltech’s Fred Raab, LIGO associate director for observatory operations. “Today we can say that our gravitational-wave network is working together brilliantly with the light-based observatories to usher in a new era in astronomy, and will improve with the planned addition of observatories in Japan and India.”
More than 1,200 scientists and some 100 institutions from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration and the Australian collaboration OzGrav. Additional partners are listed at http://ligo.org/partners.php
The Virgo collaboration consists of more than 280 physicists and engineers belonging to 20 different European research groups: six from Centre National de la Recherche Scientifique (CNRS) in France; eight from the Istituto Nazionale di Fisica Nucleare (INFN) in Italy; two in the Netherlands with Nikhef; the MTA Wigner RCP in Hungary; the POLGRAW group in Poland; Spain with the University of Valencia; and the European Gravitational Observatory, EGO, the laboratory hosting the Virgo detector near Pisa in Italy, funded by CNRS, INFN, and Nikhef.
High Res. versions of these graphics can be found in our gallery.
GW170817’s numbers
Masses of Neutron Stars and Black Holes
Current operating facilities in the global network include the twin LIGO detectors—in Hanford, Washington, and Livingston, Louisiana – Virgo in Italy, and GEO600 in Germany.
Neutron Star Merger Seen in Gravity and Matter
Virgo Helps Localize Gravitational-Wave Signals
GW170817: A Global Astronomy Event
Artist’s illustration of two merging neutron stars.
LIGO’s data shows the “chirp” sound produced as the two neutron stars inspiral.
Videos
Neutron star merger (Credit: Christopher W. Evans/Georgia Tech)
Jets and Debris from Neutron Star Collision (Credit: NASA/Goddard Space Flight Center/CI Lab)
Last Dance of Neutron Star Pair (Credit: W. Kastaun/T. Kawamura/B. Giacomazzo/R. Ciolfi/A. Endrizzi)
Ripples of Gravity, Flashes of Light (Credit: LIGO/Virgo)
Zooming in on the Source of Gravitational Waves (Credit: LIGO-Virgo)
Final Flight of Neutron Star Pair (Credit: LIGO-Virgo/Aaron Geller/Northwestern University)
Hearing the Wave (Credit: Alex Nitz/Max Planck Institute for Gravitational Physics/LIGO)
The Ellen MacArthur Foundation and the World Economic Forum, in a report called The New Plastics Economy (which looks at the amount of plastic that ends up in the sea) claims there will be more plastic than fish in the sea by 2050. “If we continue dumping plastic in the sea at the present rate, measured by weight, there will be more plastic than fish by 2050.”
The study examines just one area – San Francisco Bay. “If that’s not representative of the rest of the globe then you can see the potential for large deviations in this calculation,” says Prof Callum Roberts from the University of York.
Many days in the Philadelphia region are not healthy for breathing. On “Ozone Action Alert Days” you are advised to avoid outside activities. Children should not play outdoors. Avoid running and other fitness activities. Do not breathe in unconditioned air. Low level ozone is volatile and causes micro-explosions in your lungs that result in chronic respiratory and immune system damage. The more and harder you breathe, the more damage you cause to your body. Avoid exercise.
The Universal Theorem contains elements from: Einstein’s Theory of Relativity / Space-time Continuum, Vortex Physics, Chaos Theory and The Laws of Thermodynamics. The combination of these elements form a system. The interaction between the system and matter is commonly called time.
Imagine Earth as it starts on the edge of the vortex and slowly gets pulled toward the center and bottom… spiraling faster and faster.
Spiral Galaxy
NASA states, “Messier 74, also called NGC 628, is a stunning example of a grand-design spiral galaxy that is viewed by Earth observers nearly face-on. Its perfectly symmetrical spiral arms emanate from the central nucleus and are dotted with clusters of young blue stars and glowing pink regions of ionized hydrogen (hydrogen atoms that have lost their electrons). These regions of star formation show an excess of light at ultraviolet wavelengths.”
