Editorial: 鈥�Climate blame: send for the lawyers鈥�
BLAMING climate change for extreme weather events, like the 2010 heatwave that set the Moscow region of Russia alight in 2010 or the floods that have ravaged the UK since the 1970s (see 鈥�Atmospheric rivers cause the UK鈥檚 worst floods鈥�), is one of the hottest topics in climate science. The Russian fires are currently the subject of debate, and the stakes are high. Solving the issue could bring closer the day when disaster victims can successfully sue oil and coal companies.
Later this month, the Intergovernmental Panel on Climate Change (IPCC) will review progress on the issue. And next year, UK and US climate scientists plan to launch an annual global assessment of whether humans are to blame for the previous year鈥檚 extreme weather events. They could be busy.
Advertisement
A case in point are two separate studies which have taken a closer look at last year鈥檚 Russian heatwave. Temperatures up to 10.7 掳C above average triggered huge fires in peat bogs, killing an estimated 56,000 people.
Randall Dole of the US National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, looked at weather data from west Russia going back to 1880 and the atmospheric conditions in place in 2010, and concluded that the record-breaking temperatures were mainly due to natural variability. The immediate cause, he said, was a stationary high pressure system, known as a blocking event, hovering over the area (Geophysical Research Letters, ).
But in a study published in October, Stefan Rahmstorf and Dim Coumou of the Potsdam Institute for Climate Impact Research in Germany found that there is an 80 per cent chance that the temperature record would not have occurred without climate change (Proceedings of the National Academy of Sciences, ).
The two studies are not directly contradictory. Rahmstorf found that while most of the heatwave may have been natural, a significant warming in western Russia over 30 years 鈥� probably due to climate change 鈥� tipped the natural variability described by Dole into a dangerous red zone.
Who is right? 鈥淏oth are,鈥� says Myles Allen of the University of Oxford. 鈥淏ut I am closer to Stefan. In extreme events like the Russian heatwave, most of the impact comes from crossing a threshold.鈥� Doing so is made much more likely by climate change.
Whatever the disputes, the business of attributing blame for weather events is growing. Allen has shown that the European heatwave of 2003, which killed 35,000 people, was made twice as likely to happen by industrial greenhouse gas emissions. His colleague Pardeep Pall found the same for the UK鈥檚 floods in 2000, and Martin Hoerling, also at NOAA, has found that the magnitude and frequency of the drying around the Mediterranean is too great to be explained by natural variability alone.
The IPCC is likely to endorse these findings and warn of much worse to come when it . But not everyone agrees. Some leading researchers on climate extremes, such as Roger Pielke Jnr at the University of Colorado in Boulder, say there is no compelling proof that extreme weather events are becoming more frequent. For flooding and tropical cyclones, the two biggest threats in terms of lost property and life, Pielke . Some risks, such as killer heatwaves, may increase; but others, like cold snaps, may decrease.
The blame game got going this month when Kevin Trenberth of the US National Center for Atmospheric Research, also in Boulder, proposed changing the burden of proof for climate extremes (WIREs Climate Change, ). He said that all unusual events should be assumed to be due to human emissions, unless shown otherwise. Without this, he argues, the public will underestimate our role in climate events. Not everyone is impressed. 鈥淚t鈥檚 a rubbish idea,鈥� Allen told 麻豆传媒.
All this matters, not least because of the potential for legal action against energy companies over damage caused by weather events. In the US, for instance, victims of hurricane Katrina in Mississippi sued an energy company for contributing to the disaster with their emissions.
No such actions have succeeded so far, in large part because it is difficult to pin blame. 鈥淚鈥檓 extremely dubious that science can provide enough evidence for legal actions,鈥� says Pielke. Peter Stott of the UK Met Office in Exeter says the legal system has yet to determine the level of proof that will be required, and scientists have yet to establish agreed methodologies to prevent disagreements like that between Dole and Rahmstorf (see 鈥�My self-destructing syringe could save millions of lives鈥�).
鈥淚鈥檓 extremely dubious that science can provide enough attribution evidence for legal actions鈥�
鈥淩ahmstorf鈥檚 finding would make the rejection of causation arguments more difficult and tend to increase the prospects of private law claims succeeding,鈥� says UK lawyer Richard Lord. 鈥淭his issue is likely to become increasingly pressing if international climate negotiations fail to provide a comprehensive regulatory framework to address鈥� climate change.鈥� Allen believes that one litigation success would open the legal floodgates.
Attribution could also help decide who should receive the billions of dollars that developed nations plan to give to poorer ones to help them adapt to climate change. 鈥淲e will need at some point to demonstrate whether people receiving funds for adaptation really are being affected,鈥� says Allen. Studies proving that the extreme weather events they have experienced were caused by greenhouse gas emissions will be pivotal.
