Tag: warmer springs

bookmark_borderGlobal Warming Proof

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by the Institute for Marine and Antarctic Studies

Ocean measurements taken more than 135 years ago during the scientific expedition of HMS Challenger have provided further confirmation of human-produced global warming over the past century.

The researchers also found the thermal expansion of sea water caused by this global warming contributed to around 40 per cent of the total sea level rise seen in tide gauges from 1873 to 1955. The remaining 60 per cent was likely to have come from the melting of ice sheets and glaciers.

“Our research revealed warming of the planet can be clearly detected since 1873 and that our oceans continue to absorb the great majority of this heat,” said lead author Dr Will Hobbs, a researcher at the University of Tasmania’s Institute for Marine and Antarctic Studies and the Australian Research Council’s Centre of Excellence for Climate System Science.

“Currently scientists estimate the oceans absorb more than 90 per cent of the heat trapped by greenhouse gases, and we attribute the global warming to anthropogenic causes.”

The Challenger expedition, from 1872-1876, was the world’s first global scientific survey of life beneath the ocean surface. Along the way scientists measured ocean temperatures, lowering thermometers hundreds of metres deep on ropes made from Italian hemp during its voyage.

Researchers combined these data with modern observations and used both in state-of-the-art climate models to get a picture of how the world’s oceans have changed since the Challenger’s voyage.

“The key to this research was to determine the range of uncertainty for the measurements taken by the crew of the Challenger,” said study co-author Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory.

“After we had taken all these uncertainties into account, it became apparent that the rate of warming we saw across the oceans far exceeded the degree of uncertainty around the measurements.

“So, while the uncertainty was large, the warming signal detected was far greater.”

Uncertainties around the Challenger’s measurements were caused by the limited areas measured during the voyage; the actual depths the thermometers descended to and the likely natural variation in temperature that could occur in each region during the voyage.

To get the most reliable results the researchers used the most conservative estimates after taking into account the maximum possible variation caused by these uncertainties.

“Because we took the most conservative outcome, we are likely to have underestimated the true temperature rise,” said Dr Hobbs.

“A simple analysis of our results suggests we may have underestimated the warming by as much as 17 per cent. In fact many of the stations most prone to bias were in the Eastern Pacific – a region showing one of the strongest ocean warming trends – so the true warming may be even larger than that.”

In addition to determining the increase in temperatures, the measurements from the Challenger expedition revealed the amount of thermal expansion in sea level rise in the oceans before the 1950s. Prior to this research, climate models offered the only way to estimate the change.

“This research adds yet another suite of compelling data that shows human activity continues to have a dramatic influence on the Earth’s climate,” said Dr Hobbs.

bookmark_borderOh No Snow

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BOZEMAN, Mont. – Warmer spring temperatures since 1980 are causing an estimated 20 percent loss of snow cover across the Rocky Mountains of western North America, according to new research from the U.S. Geological Survey.

The new study builds upon a previous USGS snowpack investigation which showed that, until the 1980s, the northern Rocky Mountains experienced large snowpacks when the central and southern Rockies experienced meager ones, and vice versa. Yet, since the 1980s, there have been simultaneous snowpack declines along the entire length of the Rocky Mountains, and unusually severe declines in the north.

The new study has teased apart and quantified the different influences of winter temperature, spring temperature, and precipitation on historic snowpack variations and trends in the region. To distinguish those varying influences, the researchers implemented a regional snow model that uses inputs of monthly temperature and precipitation data from 1895 to 2011.

“Each year we looked at temperature and precipitation variations and the amount of water contained within the snowpack as of April,” said USGS scientist Greg Pederson, the lead author of the study. “Snow deficits were consistent throughout the Rockies due to the lack of precipitation during the cool seasons during the 1930s – coinciding with the Dust Bowl era. From 1980 on, warmer spring temperatures melted snowpack throughout the Rockies early, regardless of winter precipitation. The model in turn shows temperature as the major driving factor in snowpack declines over the past thirty years.”

Runoff from Rocky Mountain winter snowpack accounts for 60 to 80 percent of the annual water supply for more than 70 million people living in the western U.S., and is influenced by factors such as the snowpack’s water content, known as snow water equivalent, and the timing of snowmelt.

The timing of snowmelt affects not only when water is available for crop irrigation and energy production from hydroelectric dams, but also the risk of regional floods and wildfires. Earlier and faster snowmelt could have repercussions for water supply, risk management, and ecosystem health in western watersheds.

Regional snowpack accumulation is highly sensitive to variations in both temperature and precipitation over time. Patterns and sources of these variations are difficult to discern due to complex mountain topography, the different influence of Pacific Ocean climate, like La Niña and El Niño, on winter precipitation in the northern versus southern and central Rockies, and the brevity and patchiness of detailed snow records.

In the study, the regional snow model used by Pederson and his USGS colleagues Julio Betancourt and Greg McCabe allows estimation of snow water and cover variability at different latitudes and elevations during the last century regardless of the absence of direct and long-term observations everywhere. Recent snowpack variations also were evaluated in the context of snowpack evidence from tree-rings, allowing the scientists to compare recent observations to measurements from the past 800 years.

McCabe, co-author of the study, explains that “recent springtime warming also reduced the extent of snow cover at low to middle elevations where temperature has had the greatest impact.”

“Both natural variability in temperature and anthropogenic warming have contributed to the recent snowpack decline, though disentangling their influences exactly remains elusive.” Betancourt said,

“Regardless of the ultimate causes, continuation of present snowpack trends in the Rocky Mountains will pose difficult challenges for watershed management and conventional water planning in the American West.”

The study, “Regional patterns and proximal causes of the recent snowpack decline in the Rocky Mountains,” is available from Geophysical Research Letters, a journal of the American Geophysical Union.