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Sunday 05.02.2012

Galloping climate change

The warming trend appears to be racing ahead of the modeling that scientists have done, says Robert Corell, who chaired Arctic Climate Impact Assessment.

Robert Corell, a U.S. oceanographer who helped lead the United Nations Intergovernmental Panel on Climate Change, was in Anchorage recently where he said warming appears to be overtaking previous forecasts.



Corell chaired the Arctic Climate Impact Assessment team, a part of the IPCC effort.

In his talks in Alaska, one of Corell's main points was that the warming trend appears to be racing ahead of the modeling that scientists have done, as evidenced by recent polar ice surveys.

This means people may soon be experiencing climate and environmental changes that can't be predicted, Corell said at the conclusion of a talk at the University of Alaska Anchorage earlier this month.

Corell said the buildup of CO2 will continue toward a peak in perhaps 100 years, but even then, carbon dioxide levels would not stabilize in the atmosphere for several hundred years, and the warming trend caused by the buildup will not end for about 500 years have passed.

Even then, the atmospheric warming effects of higher temperatures in the ocean will continue, Corell said.

Corell said that the current global models can reasonably be expected to predict temperature changes in the next 100 years because they have accurately verified changes over the last century for which there is real temperature data. After 100 years, all bets are off, he said.

Global temperature measurements show we are now moving rapidly out of that comfortable temperature band, he said. Present-day temperature averages are at the top of the band. On average, global temperatures have increased 0.74 degrees C over past 100 years, according to the IPCC reports.

“The effects on the food system are expected to get worse as temperatures increase beyond 1 percent,” Corell said.

The models predict a temperature increase of 1.5 degrees C to 4.5 degrees C with the most likely increase being 2 degrees C to 3 degrees C, he said.

Climate change models have become much more sophisticated and complex. In the 1970s, the models included mainly atmospheric changes, while they now include changes induced by changed ocean conditions and increasing levels of pollutants, such as sulfur emissions.

The generation of models used in the IPCC's forecasts were developed in the 1990s and their conclusions already appear to be too conservative.

Actual changes - the rapid retreat of summer Arctic sea ice and the buildup of carbon dioxide in the atmosphere - appear to be accelerating faster than predicted.

CO2 content currently is 379 parts per million. Models predict an atmospheric CO2 content of 450 ppm by 2025 to 2030, but measurements of a 1.9 percent increase in world CO2 emissions in 2002 indicate that this buildup is occurring at a faster rate, and that 450 million ppm could be reached by 2020.

Rising ocean levels must also be considered. Melting of the Greenland and Antarctic ice sheets would cause only part of this, Corell said. Much of it will likely come from natural expansion of the water as it warms.

Average sea levels have increased an average of 8 centimetres (3 inches) over the last 20 years and Corell said most scientists believe a 1-metres increase in sea levels to be most likely in next 100 years.

Some scientists predict ocean level increases of up to four meters. This more pessimistic view results from a recent study of the last interglacial warm period initiated by the European Commission. This period spanned about 1,000 to 1,500 years between two ice ages. The temperature increase was 1 degree C on average but the ocean level increase was estimated at 4 metres, Corell said.

If Greenland were to entirely melt, which the models indicate could eventually happen, the sea level increase is estimated at about seven meters, or 23 feet.

The science teams also feel, with 95 percent certainty, that the warming is caused or strongly influenced by the buildup of greenhouse gases from industrial activity.

“We have measured a dramatic buildup of carbon dioxide, methane and nitrogen oxide in the atmosphere over the last 150 years,” essentially since the beginning of the industrial revolution, Corell said. “Something is clearly different.”

Using the global climate change models, computer simulations were done for regions of the world assuming no greenhouse gas buildup, as if the industrial revolution had never happened.

In his UAA lecture Corell showed those and compared them with simulations that took the base case (no greenhouse gases) and added effects induced by the buildup of greenhouse gases in the atmosphere. The correlation between the predicted temperature buildups in different regions and the actual temperatures measured was startling.

In the climate change discussion, much of the attention is focused on carbon dioxide, but methane is a gas that is 25 times as potent as CO2 in its greenhouse effect and methane emissions are not being measured in the U.S., although they are in Europe.

Concentrations of CO2 and methane in the atmosphere are both spiking. Corell said scientists believe 70 per cent of the methane spike can be traced to human activity.

About 25 percent to 30 per cent of the methane increase is believed coming from the decomposition of waste in landfills and the remainder of human caused releases from increasing agricultural activity. About 20 per cent to 25 per cent is believed to be from natural causes, Corell said.