By Michael Roberts - Originally published at The Next Recession, September 28, 2013
The 5th report by the International Panel for Climate Change (IPCC) was released this weekend. The IPCC brings together hundreds of scientists in the field of climate change to cooperate in drawing up a comprehensive analysis of the state of the earth’s climate and forecasts about its future. The IPCC report raised its estimate of the probability that human activities, led by the burning of fossil fuels, are the main cause of global warming since the mid-20th century to “extremely likely”, or at least 95 percent, from “very likely” (90 percent) in its previous report in 2007 and “likely” (66 percent) in 2001.
The IPCC said that short periods are influenced by natural variability and do not, in general, reflect long-term climate trends. So the argument of those whom deny global warming is man-made or is not getting worse cannot rely on the recent slowing of the rise in average atmospheric temperatures in the last 15 years. The IPCC went on to say that temperatures were likely to rise by between 0.3 and 4.8 degrees Celsius (0.5 to 8.6 Fahrenheit) by the late 21st century. Sea levels are likely to rise by between 26 and 82 cm (10 to 32 inches) by the late 21st century, after a 19 cm rise in the 19th century. In the worst case, seas could be 98 cm higher in the year 2100.
The IPCC estimates that a doubling of carbon dioxide concentrations in the atmosphere would lead to a warming of between 1.5 and 4.5 degrees Celsius (2.7 and 8.1F), lowering the bottom of the range from 2.0 degrees (3.6F) estimated in 2007 report. The new range, however, is the same as in other IPCC reports before 2007. It said the earth was set for more heatwaves, floods, droughts and rising sea levels from melting ice sheets that could swamp coasts and low-lying islands as greenhouse gases built up in the atmosphere.
The IPCC admitted that it was still unclear about the causes for the slowdown in climate change in the past 15 years, but insisted that the long-term trends were beyond doubt and that a decade and a half was far too short a period in which to draw any firm conclusions. The temperature rise has slowed from 0.12C per decade since 1951 to 0.05C per decade in the past 15 years – a point seized upon by climate skeptics to discredit climate science. Professor Stocker said:
“People always pick 1998 but that was a very special year, because a strong El Niño made it unusually hot, and since then there have been a series of medium-sized volcanic eruptions that have cooled the climate.”
Explaining a recent slower pace of warming, the report said the past 15-year period was skewed by the fact that 1998 was an extremely warm year with an El Nino event – a warming of the ocean surface – in the Pacific. It said warming had slowed “in roughly equal measure” because of random variations in the climate and the impact of factors such as volcanic eruptions when ash dims sunshine, and a cyclical decline in the sun’s output.
But the deniers of climate change and manmade global warming remain unconvinced. Professor Judith Curry of the Georgia Institute of Technology in Atlanta responded by saying that “Well, IPCC has thrown down the gauntlet – if the pause continues beyond 15 years (well it already has), they are toast.” But Rajendra Pachauri, chair of the IPCC, retorted that the reduction in warming would have to last far longer - “three or four decades” – to be a sign of a new trend. And the IPCC report predicted that the reduction in warming would not last, saying temperatures from 2016-35 were likely to be 0.3-0.7 degree Celsius (0.5 to 1.3 Fahrenheit) warmer than in 1986-2005.