I'm not sure if you can see this post because Google said ''error''when I tried to publish it on the 14th of December.
This is the third and last post about the Russian heat wave. It is written by four researchers who saw the two studies with conflicting results and decided to do their own study. The study is done by Otto, Massey, van Oldenborgh, Jones, and Allen. They published the results in Geophysical Research Letters. Their aim is to show: ‘’ that there is no substantive contradiction between these two papers, in that the same event can be both mostly internally-generated interms of magnitude and mostly externally-driven in terms of occurrence-probability’’. (Otto et al 2011)
They do this by examining the same area as Dole et al (2011), one of the other studies on the Russian heat wave. See also my post about that study. This an area between 50°–60°N, 35°–55° E. The way that the researchers such to find out if man made global warming has anything to do with the Russian heat wave they need to find out if the frequency of such events is higher in today’s climate compared with climate from the past. This is the same approach as Opperheimer et al (2011) used in their study about storm surges near New York City. They also used a dataset with mean temperatures to examine is there was any existing trend. But as both the other studies already had shown: There is no long warming trend in West Russia. So they base their study on Climate models.
First they use a stationary climate to find out how often an event such as the Russian heat wave without climate would occur, that is only once every 1,000 years with once every 250 years for the with a lower bound of the 95% confidence interval. Without warming the Russian heat wave would be very, very rare. In the study of Dole et al (2011) Then they analyse the mean temperature as a non-linear trend from 1950 and onwards with the dataset GISTEMP-1200 which suggests that between 1950 and 2009 rises with 1.9 degree Celsius. This is 0.8 times the global rise, West Russia warms slower and average. But it is significant. This is the graph of the used dataset:
There is a rise in temperature of 1.9 degree Celsius but this is less than the global average. But is trend was not only visible in the month July, the month of the heat wave but also in June and August. Although this rise in mean temperature is small it has an direct effect. Were in a stationary climate an event like the Russian heat wave only happens once per 1,000 years that number is now shrunken to 250 years with only once every 90 years by the lower bound of the 95% confidence interval.
They continue their study with trying to assess the fraction of risk of the heat wave which is attributable to external forcing (global warming). To do this they use the global circulation
model HadAM3P. This method is similar to the one used by Dole at al (2011) in their heat wave study. Their main goal with this model is to compare the 2010 Russian heat wave return levels in a climate based on the 60’s and one based on the climate in the 2000’s. To compare these climates they use regression analysis to make them better comparable. After they also removed all the bias they end up with this graph.
In the sixties climate a heat wave the size of the 2010 heat wave occurred only once every 99 years according to the authors but in the 2000’s climate it happen once every 33 years, much more often.
The authors say the following about why this graph should support the notion that the two other studies don’t contradict: The graph shows return times of the heat wave conditions for the 1960s (green) and 2000s (blue). The threshold exceeded in 2010 is shown by the solid horizontal line, which is more than 5°C above 1960s mean July temperatures, shown by the dashed line. The difference between the green and the blue lines could be characterized as a 1°C increase in the magnitude of a 33-year event as shown by the vertical red arrow. This arrow is substantially smaller than the size of the anomaly itself, supporting the assertion that the event was “mainly natural” in terms of magnitude which is consistent with Dole et al (2011) Alternatively it could be characterized
as a three-fold increase in the risk of the 2010 threshold being exceeded, supporting the assertion that the risk of the event occurring was mainly attributable to the external trend as also stated by Rahmstorf and Coumou
Cited from Otto et al (2011)
That authors this article say is that both the studies are right. Dole et al is right because the heat waves in the sixties are almost as extreme as those in the 2000’s. The magnitude is still the same. Global warming does not make heat waves more extreme than they were before. From is point of view there is no reason to assume that global warming has an influence. But Rahmstorf and Coumou are also right because although the heat waves are not increasing in magnitude they occur more often in the 2000’s than in the sixties which is in line with the findings of their study.
But was the Russian heat wave more warming driven or nature driven? There will always be a lot debate about what can be attributed to global warming and what is caused by nature. Weather, climate and global warming are not easy to predict and will remain a source of debate and research. There are many more studies about scientists who are trying to find out if a specific extreme weather event was influenced by global warming or not. Examples are:
Floods in England and Wales 2000 Here
The 2010 cold winter in Europe Here
The cold year of 2008 in the USA Here
Otto, Massey, van Oldenborgh, Jones, Allen (2012), Reconciling two approaches to attribution of the 2010 Russian heat wave, Geophys. Res. Lett., 39, L04702, Here
Dole et al (2011) Was there a basis for anticipating the 2010 Russian heat wave. Geophysical Research Letters VOL. 38,Here
Rahmstorf, Coumou ( 2011) Increase of extreme events in a warming world. Proceedings of the National Academy of Sciences, vol. 108, issue 44, pp. 17905-17909 Here
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