The Current Wisdom is a monthly series in which Senior Fellow Patrick J. Michaels reviews interesting items on global warming in the scientific literature that may not have received the media attention that they deserved, or have been misinterpreted in the popular press.
The Current Wisdom only comments on science appearing in the refereed, peer-reviewed literature, or that has been peer-screened prior to presentation at a scientific congress.
The recent publication of two articles in Nature magazine proclaiming a link to rainfall extremes (and flooding) to global warming, added to the heat in Russia and the floods in Pakistan in the summer of 2010, and the back-to-back cold and snowy winters in the eastern U.S. and western Europe, have gotten a lot of public attention. This includes a recent hearing in the House of Representatives, despite its Republican majority. Tying weather extremes to global warming, or using them as "proof" that warming doesn't exist (see: snowstorms), is a popular rhetorical flourish by politicos of all stripes.
The hearing struck many as quite odd, inasmuch as it is much clearer than apocalyptic global warming that the House is going to pass meaningless legislation commanding the EPA to cease and desist from regulating greenhouse gas emissions. "Meaningless" means that it surely will not become law. Even on the long-shot probability that it passes the Senate, the President will surely veto, and there are nowhere near enough votes to override such an action.
Perhaps "wolf!" has been cried yet again. A string of soon-to-be-published papers in the scientific literature finds that despite all hue and cry about global warming and recent extreme weather events, natural climate variability is to blame.
Where to start? How about last summer's Russian heat wave?
The Russian heat wave (and to some degree the floods in Pakistan) have been linked to the same large-scale, stationary weather system, called an atmospheric "blocking" pattern. When the atmosphere is "blocked" it means that it stays in the same configuration for period of several weeks (or more) and keeps delivering the same weather to the same area for what can seem like an eternity to people in the way. Capitalizing on the misery in Russia and Pakistan, atmospheric blocking was added to the list of things that were supposed to be "consistent with" anthropogenically stimulated global warming which already, of course included heat waves and floods. And thus the Great Russian Heat Wave of 2010 became part of global warming lore.
But then a funny thing happened — scientists with a working knowledge of atmospheric dynamics started to review the situation and found scant evidence for global warming.
The first chink in the armor came back in the fall of 2010, when scientists from the Physical Sciences Division (PSD) of the Earth System Research Laboratory (ESRL) of the National Oceanic and Atmospheric Administration (NOAA) presented the results of their preliminary investigation on the web , and concluded that "[d]espite this strong evidence for a warming planet, greenhouse gas forcing fails to explain the 2010 heat wave over western Russia. The natural process of atmospheric blocking, and the climate impacts induced by such blocking, are the principal cause for this heat wave."
The PSD folks have now followed this up with a new peer-reviewed article in the journal Geophysical Research Letters that rejects the global warming explanation. The paper is titled "Was There a Basis for Anticipating the 2010 Russian Heat Wave?" Turns out that there wasn't.
To prove this, the research team, led by PSD's Randall Dole, first reviewed the observed temperature history of the region affected by the heat wave (western Russia, Belarus, the Ukraine, and the Baltic nations). To start, they looked at the recent antecedent conditions: "Despite record warm globally-averaged surface temperatures over the first six months of 2010, Moscow experienced an unusually cold winter and a relatively mild but variable spring, providing no hint of the record heat yet to come." Nothing there.
Then they looked at the long-term temperature record: "The July surface temperatures for the region impacted by the 2010 Russian heat wave shows no significant warming trend over the prior 130-year period from 1880 to 2009... . A linear trend calculation yields a total temperature change over the 130 years of -0.1Â°C (with a range of 0 to -0.4Â°C over the four data sets [they examined])." There's not a hint of a build-up to a big heat wave.
And as to the behavior of temperature extremes: "There is also no clear indication of a trend toward increasing warm extremes. The prior 10 warmest Julys are distributed across the entire period and exhibit only modest clustering earlier in this decade, in the 1980s and in the 1930s... . This behavior differs substantially from globally averaged annual temperatures, for which eleven of the last twelve years ending in 2006 rank among the twelve warmest years in the instrumental record since 1850... ."
With regard any indication that "global" warming was pushing temperatures higher in Russia and thus helped to fuel the extreme heat last summer, Dole et al. say this: "With no significant long-term trend in western Russia July surface temperatures detected over the period 1880-2009, mean regional temperature changes are thus very unlikely to have contributed substantially to the magnitude of the 2010 Russian heat wave."
Next the PSD folks looked to see if the existing larger-scale antecedent conditions, fed into climate models would produce the atmospheric circulation patterns (i.e. blocking) that gave rise to the heat wave. The tested "predictors" included patterns of sea surface temperature and arctic ice coverage, which most people feel have been subject to some human influence. No relationship: "These findings suggest that the blocking and heat wave were not primarily a forced response to specific boundary conditions during 2010."
In fact, the climate models exhibited no predilection for projecting increases in the frequency of atmospheric blocking patterns over the region as greenhouse gas concentrations increased. Just the opposite: "Results using very high-resolution climate models suggest that the number of Euro-Atlantic blocking events will decrease by the latter half of the 21st century."
At this point, Dole and colleagues had about exhausted all lines of inquiry and summed things up:
Our analysis points to a primarily natural cause for the Russian heat wave. This event appears to be mainly due to internal atmospheric dynamical processes that produced and maintained an intense and long-lived blocking event. Results from prior studies suggest that it is likely that the intensity of the heat wave was further increased by regional land surface feedbacks. The absence of long-term trends in regional mean temperatures and variability together with the model results indicate that it is very unlikely that warming attributable to increasing greenhouse gas concentrations contributed substantially to the magnitude of this heat wave.
Can't be much clearer than that.
But that was last summer. What about the past two winters? Both were very cold in the eastern U.S. with record snows events and/or totals scattered about the country.
Cold, snow, and global warming? On Christmas Day 2010, the New York Times ran an op-ed by Judah Cohen, a long-range forecaster for the private forecasting firm Atmospheric and Environmental Research, outlining his theory as to how late summer Arctic ice declines lead to more fall snow cover across Siberia which in turn induces atmospheric circulation patterns to favor snowstorms along the East Coast of the U.S. Just last week, the Union of Concerned Scientists held a news conference where they handed out a press release  headlined "Climate Change Makes Major Snowstorms Likely." In that release, Mark Serreze, director of the National Snow and Ice Data Center, laid out his theory as to how the loss of Arctic sea ice is helping to provide more moisture to fuel winter snowstorms across the U.S. as well as altering atmospheric circulation patterns into a preferred state for big snowstorms. Weather Underground's Jeff Masters chimed in with "Heavy snowstorms are not inconsistent with a warming planet."
As is the wont for this Wisdom, let's go back to the scientific literature.
Another soon-to-be released paper to appear in Geophysical Research Letters describes the results of using the seasonal weather prediction model from the European Center for Medium-Range Weather Forecasts (ECMWF) to help untangle the causes of the unusual atmospheric circulation patterns that gave rise to the harsh winter of 2009-2010 on both sides of the Atlantic. A team of ECMWF scientists led by Thomas Jung went back and did experiments changing initial conditions that were fed into the ECMWF model and then assessed how well the model simulated the known weather patterns of the winter of 2009-2010. The different set of initial conditions was selected so as to test all the pet theories behind the origins of the harsh winter. Jung et al. describe their investigations this way: "Here, the origin and predictability of the unusual winter of 2009/10 are explored through numerical experimentation with the ECMWF Monthly forecasting system. More specifically, the role of anomalies in sea surface temperature (SST) and sea ice, the tropical atmospheric circulation, the stratospheric polar vortex, solar insolation and near surface temperature (proxy for snow cover) are examined."
Here is what they found after running their series of experiments.
Arctic sea ice and sea surface temperature anomalies. These are often associated with global warming caused by people. Finding: "These results suggest that neither SST nor sea ice anomalies explain the negative phase of the NAO during the 2009/10 winter."
(NAO are the commonly used initials for the North Atlantic Oscillation — and atmospheric circulation pattern that can act to influence winter weather in the eastern U.S. and western Europe. A negative phase of the NAO is associated with cold and stormy weather and during the winter of 2009-10, the NAO value was the lowest ever observed.)
A global warming-induced weakening stratospheric (upper-atmosphere) jetstream. "Like for the other experiments, these stratospheric relaxation experiments fail to reproduce the magnitude of the observed NAO anomaly."
Siberian snow cover. "The resulting [upper air patterns] show little resemblance with the observations... . The implied weak role of snow cover anomalies is consistent with other research... ."
Solar variability. "The experiments carried out in this study suggest that the impact of anomalously low incoming [ultraviolet] radiation on the tropospheric circulation in the North Atlantic region are very small... suggesting that the unusually low solar activity contributed little, if any, to the observed NAO anomaly during the 2009/10 winter."
Ok then, well what did cause the unusual weather patterns during the 2009-10 winter?
The results of this study, therefore, increase the likelihood that both the development and persistence of negative NAO phase resulted from internal atmospheric dynamical processes.
Translation: Random variability.
To drive this finding home, here's another soon-to-be-released paper (D'Arrigo et al., 2001) that uses tree ring-based reconstructions of atmospheric circulation patterns and finds a similar set of conditions (including a negative NAO value second only to the 2009-10 winter) was responsible for the historically harsh winter of 1783-84 in the eastern U.S. and western Europe, which was widely noted by historians. It followed the stupendous eruption of the Icelandic volcano Laki the previous summer. The frigid and snowy winter conditions have been blamed on the volcano. In fact, Benjamin Franklin even commented as much.
But in their new study, Roseanne D'Arrigo and colleagues conclude that the harshness of that winter primarily was the result of anomalous atmospheric circulation patterns that closely resembled those observed during the winter of 2009-10, and that the previous summer's volcanic eruption played a far less prominent role:
Our results suggest that Franklin and others may have been mistaken in attributing winter conditions in 1783-4 mainly to Laki or another eruption, rather than unforced variability.
Similarly, conditions during the 2009-10 winter likely resulted from natural [atmospheric] variability, not tied to greenhouse gas forcing... Evidence thus suggests that these winters were linked to the rare but natural occurrence of negative NAO and El NiÃ±o events.
The point is that natural variability can and does produce extreme events on every time scale, from days (e.g., individual storms), weeks (e.g., the Russian heat wave), months (e.g., the winter of 2009-10), decades (e.g., the lack of global warming since 1998), centuries (e.g., the Little Ice Age), millennia (e.g., the cycle of major Ice Ages), and eons (e.g., snowball earth).
Folks would do well to keep this in mind next time global warming is being posited for the weather disaster du jour. Almost assuredly, it is all hype and little might.
Too bad these results weren't given a "hearing" in the House!
D'Arrigo, R., et al., 2011. The anomalous winter of 1783-1784: Was the Laki eruption or an analog of the 2009--2010 winter to blame? Geophysical Research Letters, in press.
Dole, R., et al., 2011. Was there a basis for anticipating the 2010 Russian heat wave? Geophysical Research Letters, in press.
Jung et al., 2011. Origin and predictability of the extreme negative NAO winter of 2009/10. Geophysical Research Letters, in press.
Min, S-K., et al., 2011. Human contribution to more-intense precipitation extremes. Nature, 470, 378-381.
Pall, P., et al., 2011. Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000. Nature, 470, 382-386.