The Achilles' Heel of the International Panel on Climate Change reports is the fact they're consensus-based. That means representatives from countries that want to drag their heels on slashing greenhouse gas emissions can withhold their approval until the reports finally emerge seriously watered down.
That the reports are unduly optimistic has been borne out by the number of IPCC forecasts which have turned out to be understated. Again and again we've seen that the forecast speed of change has been understated, the degree of change is routinely understated and the frequency of change effects is regularly understated.
Yet governments and international bodies tend to treat the reports as "worst case" scenarios, impacts that could possibly occur at some time in the distant future, and they act accordingly. To accept them as "best case" scenarios would trigger a broad gamut of remedial and adaptive measures that we're just not seeing.
This weekend, Dr Chris Field, co-chair of the UN's IPCC and director of global ecology at the Carnegie Institute, told the American Association for the Advancement of Science meeting in Chicago at the weekend that the IPCC's last report on climate change in 2007 had substantially underestimated the severity of global warming over the rest of the century. From The Guardian:
The report concluded that the Earth's temperature is likely to rise between 1.1C and 6.4C by 2100, depending on future global carbon emissions. "We now have data showing that from 2000 to 2007, greenhouse gas emissions increased far more rapidly than we expected, primarily because developing countries, like China and India, saw a huge upsurge in electric power generation, almost all of it based on coal," Field said. The next report, which Field will oversee, is due in 2014 and will now include future scenarios where global warming is far more serious than previous reports have suggested, he said.
Field warned the assembled scientists that the tropical rainforests could soon turn into tinderboxes.
"Tropical forests are essentially inflammable. You couldn't get a fire to burn there if you tried. But if they dry out just a little, the result can be very large and destructive wildfires. It is increasingly clear that as you produce a warmer world, lots of forested areas that had been acting as carbon sinks could be converted to carbon sources," he said. The result could lead to runaway warming.
Field's warning was echoed by French scientists, who said the IPCC's estimate that sea levels would rise around 40cm by 2100 was likely to be a best case scenario.
The top IPCC officials tell us their reports are understated. Their warnings keep getting proven by the pace, degree and frequency of observed change. Why then do our leaders treat the IPCC reports as realistic and reliable? I'm sure it's not intentional, but the IPCC may just be enabling an awful lot of heel-dragging that will exact a severe price as this century progresses.