Tag: ocean temperature

bookmark_borderAntarctic Glacial Ice Melt

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Australia’s ABC news reports:

Scientists hope to discover how warm water is reaching one of the world’s largest glaciers, causing it to melt rapidly.

Lead author Steve Rintoul said it was the first time scientists had been able to test the hypothesis that warm ocean waters were driving the glacier’s thinning.

“We knew the Totten has been thinning faster than other glaciers in East Antarctica, but nobody has known exactly why until we took these measurements,” he said.

“We found that warmer ocean water is reaching the cavity through this channel at temperatures capable of melting the ice shelf at the point where it meets ground.

Dr Rintoul said it was important to be able to predict the Totten glacier’s future behaviour, because it contained enough sea ice to raise global sea levels by about 3.5 metres.

“So the real importance of the research is that it helps provide some clues about how sea level might change in the future.”

The publication of the research today comes as scientists make their way back to the Totten glacier, where they hope to find more clues about what controls the amount of warm water reaching the glacier.

A team of about 30 scientists, technicians and PhD students left Hobart on December 8 and plan to arrive at the glacier in late December.

Dr. Rintoul said their goal was to learn more about the pathways that bring the warm water up from the deep ocean.

“Understanding the physical processes delivering heat to the ice shelf will help us assess the vulnerability of the East Antarctic ice sheet to future changes in the Southern Ocean,” he said.

“What we have shown is that warm water reaches the glacier. What we need to know is what’s going to happen in the future.

Dr. Tas van Ommen from the Australian Antarctic Division said it would be concerning to see an increase in the Totten glacier’s natural melt rate.

“If its natural melt rate was to increase because of changes in ocean circulation, that would then add to the sea level rise that we see from glaciers already melting in Antarctica, particularly in the West.

“So we are concerned to track that and to be able to predict what might happen in the future.”

bookmark_borderWhy Doesn’t Global Warming Feel Warmer?

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The Intergovernmental Panel on Climate Change (IPCC) has released its Fifth Assessment Report (AR5). The report states that “warming of the climate system is unequivocal.”

Then, why doesn’t it feel that much hotter? Because most of the rise in temperature is in the water:

Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0?700 m) warmed from 1971 to 2010, and it likely warmed between the 1870s and 1971.

• On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971–2010. Since AR4, instrumental biases in upper-ocean temperature records have been identified and reduced, enhancing confidence in the assessment of change.
• It is likely that the ocean warmed between 700 and 2000 m from 1957 to 2009. Sufficient observations are available for the period 1992 to 2005 for a global assessment of temperature change below 2000 m. There were likely no significant observed temperature trends between 2000 and 3000 m for this period. It is likely that the ocean warmed from 3000 m to the bottom for this period, with the largest warming observed in the Southern Ocean.
• More than 60% of the net energy increase in the climate system is stored in the upper ocean (0–700 m) during the relatively well-sampled 40-year period from 1971 to 2010, and about 30% is stored in the ocean below 700 m. The increase in upper ocean heat content during this time period estimated from a linear trend is likely.
• It is about as likely as not that ocean heat content from 0–700 m increased more slowly during 2003–2010 than during 1993–2002. Ocean heat uptake from 700–2000m, where interannual variability is smaller, likely continued unabated from 1993 to 2009.
• It is very likely that regions of high salinity where evaporation dominates have become more saline, while regions of low salinity where precipitation dominates have become fresher since the 1950s. These regional trends in ocean salinity provide indirect evidence that evaporationand precipitation over the oceans have changed (medium confidence).
• There is no observational evidence of a trend in the Atlantic Meridional Overturning Circulation (AMOC), based on the decade-long record of the complete AMOC and longer records of individual AMOC components.