Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
Today’s global media are ablaze with coverage of newly reported scientific findings purporting to show that anthropogenic global warming is leading to more extreme weather events such as heat waves, forest fires, and floods.
The findings are being made available in the early releases section of the Proceedings of the National Academy of Sciences (PNAS) and represent the work of a group of researchers from the Potsdam Institute for Climate Impact Research (PIK)—an institute which can be routinely counted on to produce rather alarming climate change studies. The new analysis, led by Vladimir Petoukhov, is no exception.
The researchers examined the trends in the daily patterns of air flow in the lower atmosphere and found that some patterns had become more persistent with time—a characteristic that leads to a slowdown in the forward motion of weather systems. Or as the researchers put it in their press release, “What we found is that during several recent extreme weather events these planetary waves almost freeze in their tracks for weeks.” To make sure you understand the implications, they added “Since many ecosystems and cities are not adapted to this, prolonged hot periods can result in a high death toll, forest fires, and dramatic harvest losses.”
While climate alarm plays well in the media, what doesn’t play so well is climate-as-normal.
Case and point: there are zero media stories about a similarly timed study purporting to show that any anthropogenic global warming influence on extreme weather events is too small to be reliably detected.
This study, available in the early-release section of the journal Geophysical Research Letters, was performed by the research team of James Screen and Ian Simmonds of the University of Melbourne. Screen and Simmons examined the trends in the daily patterns of air flow in the lower atmosphere and found little significant change. They note that “the changes in meridional amplitude over recent decades are relatively small compared to the year-to-year variability” and “that possible connections between [anthropogenic global warming] and planetary waves, and the implications of these, are sensitive to how waves are conceptualized.” They cautiously conclude that “[t]he contrasting meridional and zonal amplitude trends have different and complex possible implications for midlatitude weather, and we encourage further work to better understand these.”
[Layman’s translation: There are few significant changes in north-to-south extent of jet stream troughs or their forward speed. The data are so noisy that results are highly dependent upon what analytical method is chosen. The contrasting north-south and east-west changes in jet stream troughs have multiple influences that we haven’t sorted out yet, but it would be foolish to tie them to global warming at this time.]