by Judith Curry
In Part I, I was very unconvinced by strategies for attributing extreme events to global warming. Today, two new papers have been published in Nature that attribute the recent heavy rains to global warming. For a summary, see this article linked to at Huffington Post. The article said:
Most of the 10 outside climate experts who reviewed the papers for The Associated Press called the research sound and strong.
However, climate scientist Jerry North of Texas A&M University, while praising the work, said he worried that the studies were making too firm a connection based on weather data that could be poor in some locations. But Francis Zwiers of the University of Victoria, a lead author of the study with Zhang, said the data was from National Weather Service gauges and is reliable.
“Put the two papers together and we start to see an emerging pattern,” said Andrew Weaver of the University of Victoria, who wasn’t part of either study. “We should continue to expect increased flooding associated with increased extreme precipitation because of increasing atmospheric greenhouse gas. And we have no one to blame but ourselves.”
I was one of the 10 outside experts interviewed by Seth Borenstein, my brief email reply to him was:
Hi Seth, limited time at the moment, but i did do a blog post on this general topic.
Here are the abstracts of the papers:
Human contribution to more intense precipitation
Seung-Ki Min, Xuebin Zhang, Francis W. Zwiers1 & Gabriele C. Hegerl
Extremes of weather and climate can have devastating effects on human society and the environment1,2. Understanding past changes in the characteristics of such events, including recent increases in the intensity of heavy precipitation events over a large part of the Northern Hemisphere land area, is critical for reliable projections of future changes. Given that atmospheric water-holding capacity is expected to increase roughly exponentially with temperature—and that atmospheric water content is increasing in accord with this theoretical expectation—it has been suggested that human- influenced global warming may be partly responsible for increases in heavy precipitation. Because of the limited availability of daily observations, however, most previous studies have examined only the potential detectability of changes in extreme precipita- tion through model–model comparisons. Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas. These results are based on a comparison of observed and multi-model simulated changes in extreme precipita- tion over the latter half of the twentieth century analysed with an optimal fingerprinting technique. Changes in extreme precipita- tion projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.
Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000
Pardeep Pall, Tolu Aina, Da ́ith ́i A. Stone, Peter A. Stott, Toru Nozawa, Arno G. J. Hilberts, Dag Lohmann & Myles R. Allen
Interest in attributing the risk of damaging weather-related events to anthropogenic climate change is increasing1. Yet climate models used to study the attribution problem typically do not resolve the weather systems associated with damaging events2 such as the UK floods of October and November 2000. Occurring during the wettest autumn in England and Wales since records began in 17663,4, these floods damaged nearly 10,000 properties across that region, dis- rupted services severely, and caused insured losses estimated at £1.3 billion (refs 5, 6). Although the flooding was deemed a ‘wake- up call’ to the impacts of climate change at the time7, such claims are typically supported only by general thermodynamic arguments that suggest increased extreme precipitation under global warming, but fail8,9 to account fully for the complex hydrometeorology4,10 asso- ciated with flooding. Here we present a multi-step, physically based ‘probabilistic event attribution’ framework showing that it is very likely that global anthropogenic greenhouse gas emissions substan- tially increased the risk of flood occurrence in England and Wales in autumn 2000. Using publicly volunteered distributed comput- ing11,12, we generate several thousand seasonal-forecast-resolution climate model simulations of autumn 2000 weather, both under realistic conditions, and under conditions as they might have been had these greenhouse gas emissions and the resulting large-scale warming never occurred. Results are fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth- century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.