The final draft of the report from a panel of the world's top climate scientists paints a wild future for a world already weary of weather catastrophes costing billions of dollars. The report says costs will rise and perhaps some locations will become "increasingly marginal as places to live."
The report from the Nobel Prize-winning Intergovernmental Panel on Climate Change will be issued in a few weeks, after a meeting in Uganda. It says there is at least a two-in-three probability that weather extremes have already worsened because of man-made greenhouse gases.
This marks a change in climate science from focusing on subtle changes in daily average temperatures to concentrating on the harder-to-analyse freak events that grab headlines, cause economic damage and kill people. The most recent bizarre weather extreme, the pre-Halloween snowstorm in the US, is typical of the damage climate scientists warn will occur – but it's not typical of the events they tie to global warming.
"The extremes are a really noticeable aspect of climate change," said Jerry Meehl, senior scientist at the National Center for Atmospheric Research. "I think people realise that the extremes are where we are going to see a lot of the impacts of climate change."
The snow-bearing Nor'easter cannot be blamed on climate change and probably isn't the type of storm that will increase with global warming, four meteorologists and climate scientists said. They agree more study is needed. But experts on extreme storms have focused more closely on the increasing numbers of super-heavy rainstorms, not snow, Nasa climate scientist Gavin Schmidt said.
The opposite kind of disaster – the drought in Texas and the south-west US – is also the type of event scientists are saying will happen more often as the world warms, said Schmidt and Meehl, who reviewed part of the climate panel report. No studies have specifically tied global warming to the drought, but it is consistent with computer models that indicate current climate trends will worsen existing droughts, Meehl said.
Studies also have predicted more intense monsoons with climate change. Warmer air can hold more water and puts more energy into weather systems, changing the dynamics of storms and where and how they hit.
Thailand is now coping with massive flooding from monsoonal rains that illustrate how climate is also interconnected with other manmade issues such as population and urban development, river management and sinking lands, Schmidt said. In fact, the report says that "for some climate extremes in many regions, the main driver for future increases in losses will be socioeconomic in nature" rather than greenhouse gases.
The report, which needs approval by diplomats at the mid-November meeting, tries to measure the confidence scientists have in their assessment of climate extremes both future and past.
Chris Field, one of the leaders of the climate change panel, said he and other authors won't comment because the report still is subject to change. The summary chapter of the report didn't detail which regions of the world might suffer extremes so severe as to leave them marginally habitable.
The report does say scientists are "virtually certain" – 99% – that the world will have more extreme spells of heat and fewer of cold. Heat waves could peak as much as 5C hotter by mid-century and even 9C hotter by the end of the century.
Weather Underground meteorology director Jeff Masters, who wasn't involved in the study, said in the United States from June to August this year, blistering heat set 2,703 daily high temperature records, compared with only 300 cold records during that period, making it the hottest summer in the US since the Dust Bowl of 1936.
By the end of the century, the intense, single-day, heavy rainstorms that now typically happen only once every 20 years are likely to happen about twice a decade, the report says.
The report said hurricanes and other tropical cyclones – like 2005's Katrina – are likely to get stronger in wind speed, but won't increase in number and may actually decrease. Massachusetts Institute of Technology meteorology professor Kerry Emanuel, who studies climate's effects on hurricanes, disagrees and believes more of these intense storms will occur.
And global warming isn't the sole villain in future climate disasters, the climate report says. An even bigger problem will be the number of people – especially the poor – who live in harm's way.
University of Victoria climate scientist Andrew Weaver, who wasn't among the authors, said the report was written to be "so bland" that it may not matter to world leaders.
But Masters said the basics of the report seem to be proven true by what's happening every day. "In the US, this has been the weirdest weather year we've had for my 30 years, hands down. Certainly this October snowstorm fits in with it."