Global warming, climate conservatism

The signs of change in the global climate are clear: glaciers are melting, the snow is in early spring and the temperatures are rising. However, the international consensus document may underestimate the value of the climate change problem

David Baylo, Scientific American

The signs of change in the global climate are clear: glaciers are melting, the snow is in early spring and the temperatures are rising. In fact, 11 of the past 12 years have been among the warmest on record. After deliberation, the scientists and diplomats of the Intergovernmental Panel on Climate Change (IPCC) published their long-awaited summary report in February 2007. The summary describes the evidence for global warming as "unequivocal" but does not mention the trend of acceleration in warming. Avoiding controversial statements and strictly sticking to data published in professional journals, caused the IPCC to issue a conservative document that may underestimate the changes that global warming will cause, as their report did in 2001.
More than 2,000 scientists from 154 countries participated in the process of producing the IPCC report, which will publish three more reports in 2007. The first report looked only at the physical science of climate change. The panel recruited senior scientists to write the main chapters on various topics, from a historical overview of climate change science to regional projections. Other governments and critics subsequently submitted more than 30,000 comments. And in the end, the writers and diplomats gathered in Paris to scrutinize every word in the final document, to change a certain emphasis in one place (the phrase "unambiguous" won over the phrase "visible") or to omit a controversial finding in another place.
For example, after objections expressed by Saudi Arabia and China, a sentence was omitted from the report which said that the effect of human activity on the Earth's heat balance is five times greater than the effect of the sun. "The actual difference is tenfold," said one of the lead authors, Piers Forrester of the University of Leeds in England: Today, the sun receives 0.12 watts more power than before per square meter on the Earth's surface, while man-made sources capture another 1.6 watts per square meter.
Conservatism is everywhere
The document's conservatism also reflects the nature of climate change science. Models of various possible scenarios predict that sea levels will rise from 18 to 59 centimeters. However, none of these models include all the larger contributions that may be added due to the melting of the Greenland and Antarctic ice sheets. The creators of these models cannot include the effects of land ice in these areas, because they cannot formulate them in equations along the lines of "X amount of excess heat causes Y amount of melting".
Greenland's glaciers are melting and moving faster on average, but these changes are not occurring at a simple, uniform increasing rate. For example, the Kangardlogsuak glacier has lost mass as a result of melting, and in its thinner form has less weight to push the ice towards the sea. In addition, about 80% of the recent increase in the release of water from the glacier occurred during only one year, before the increase stabilized. So claims Ian Howat from the University of Washington.
Glacier researcher Richard Ely of Pennsylvania State University adds: "The ice sheet is losing mass, this loss has increased over time, it is not the main factor in sea level rise, but it is having an effect." In fact, many variables are at work on the Greenland ice sheet. "We are trying to understand what is happening inside a vast, remote and complex wild animal, and it is not easy," says Eli.
Other important factors, such as heat convection that causes thunderstorms, can only be approximated because they occur on too small a scale. "The models are in no way capable of simulating these things directly," says climate modeler Stefan Zabiak of Columbia University. "That's why the researchers are trying to assess the overall impact of the processes."
Despite these flaws, the global models are becoming more and more accurate: when you feed into them the factors that have influenced the climate in the last hundred years, the results they produce match the actual observations. This accuracy gives scientists greater confidence in their ability to assign probabilities to future occurrences. All models agree that the world will warm by at least 0.4 degrees Celsius in the next 20 years.
In April 2007, the IPCC published its second report, which focuses on the effects of global warming, from more severe droughts to heavy rainfall and other extreme weather events. The third report, which should be published this month, deals with options for dealing with the problem, such as alternatives to mineral fuel. The commitment to such alternatives in the US is still weak - the budget for research into biofuels and hydrogen has increased, but funding for other alternative energy sources has decreased. The total budget for these studies is lower than the one allocated by the USA to the subject in the 70s.
Aly says that "at least some of the students feel that the support for research into energy solutions and global warming is still not reliable enough for them to dedicate their future to the field." Given the IPCC's conservative estimates, the need for such solutions is clear.

The climate crystal ballDespite remaining uncertainties, global climate prediction models are becoming more accurate and allow researchers to confidently determine "the range of different scenarios and their likelihood," says climate model developer Stefan Zabiak of Columbia University. The models agree that the Earth will warm by 0.4 degrees Celsius in the next 20 years.
Even if greenhouse gas emissions were to stop today, the Earth would warm by 0.6 degrees by the end of the century due to the heat already absorbed in the oceans and the long-term effects of the carbon dioxide in the atmosphere.
If the concentration of carbon dioxide in the atmosphere doubles compared to the pre-industrial levels of about 280 parts per million (ppm), the global temperature will rise by 3 degrees Celsius, according to the best estimate of the Intergovernmental Panel on Climate Change. At the end of 2005, the atmosphere contained 379 ppm carbon dioxide - a level that had not been seen for at least 650,000 thousand years.