David Whitehouse: Extreme Views About Extreme Events
In the past few years it has been the desire of some scientists to link extreme weather events to climate change. Climate change has become climate disruption.
The idea is to take the real world and compare it to a model one, a world in which mankind has had no influence. There should be a difference due to the increased temperature affecting parameters like humidity that will cause human-induced changes in hot spells, droughts, rainfall, hurricanes etc. The problem is, of course, in modeling the world without humans when we don’t know the way the world would have been without us, or exactly how the world has changed with us.
Some were quick to assign a human influence to the Russian heatwave of 2010 and the more recent drought in the USA. In the recent past news reports in the UK concerning flooding which is more frequent these days for many reasons, almost always mentioned climate change. Some scientists were saying that they were “increasingly confident” that the recent Russian heatwave was due to mankind. One scientist even went as far to suggest that all extreme weather events were caused by global warming unless proven otherwise!
There were warning signs that this was perhaps going too far. In the Autumn of 2011 a paper in the PNAS said that there was an 80% chance that the Russian heatwave would not have occurred without man-made global warming. NOAA said that it was mainly due to natural variability.
It was said that due to man-made global warming the weather system was biased and that there would be a greater frequency of extreme events. No individual event could be attributed to climate change it was emphasised but collectively they would show the influence of mankind. The problem was that the statistics of the changing frequency of extreme events was poor and didn’t really prove anything. Hurricanes even seemed to have decreased in frequency. Some questioned if attribution would ever be possible, at least in our lifetimes.
In March 2012 the IPCC issued a report on extreme climatic events and climate change attribution and was sure there was good evidence for a link. It said: Evidence suggests that climate change has led to changes in climate extremes such as heat waves, record high temperatures and, in many regions, heavy precipitation in the past half century… The main message from the report is that we know enough to make good decisions about managing the risks of climate-related disasters.
Today’s issue of the journal Nature contains a landmark editorial that reigns back from such extreme talk. Contradicting the IPCC it says that the science is too immature to attribute individual events to climate change. In essence the Nature Editorial says that the standard of proof accepted by some scientists would not be good enough for the courts.
The legal profession has not always been able to take the best out of science and apply it to practical law. Conversely science has not always appreciated the nature of legal proof. The early use of dna evidence in criminal proceedings is an example. Looking back at the way statistics and probabilities were used shows that in some cases lawyers and scientists were not looking at the science the same way. Although some scientists bemoaned this mismatch the result was that lawyers forced scientists to be more rigorous when their opinions and judgments were tested in courts and often found wanting. Because science hadn’t done so itself the legal profession brutally weeded out speculation from fact. Science benefited from this rigour.
Nature says that attribution is in its infancy. How does that square with recent comments by Nasa’s James Hansen, “We are certainly seeing climate change in action…This year has been exceptionally unusual throughout the United States.” Writing in this morning’s Guardian Connie Hedegaard, the European Commissioner for Climate Action, says that ‘extreme’ weather is the new normal: “We are now confident about linking individual events to climate change,” she maintains.
Perhaps she should read the Nature editorial.