Guest Post By Thomas N. Chase
Chase, T.N., K. Wolter, R.A. Pielke Sr., and Ichtiaque Rasool, 2006: Was the 2003 European summer heat wave unusual in a global context? Geophys. Res. Lett., 33, L23709, doi:10.1029/2006GL027470.
In Chase et al. (2006) we documented the June, July, and August averaged thickness temperature anomalies in terms of standard deviations exceeded and concluded that, while the European heatwave was unusual, natural variability in terms of ENSO and volcanic eruptions exceeded the extremes of the European heatwave. In subsequent commentary on this paper, Connelly (2006) found that the European heat wave was indeed quite unusual if surface temperature data was used prompting Chase et al. (2008) to conclude, along with others, that the unusual heat wave was confined near the surface was the result of surface processes and not a general warming of the troposphere as would be expected in a global warming scenario. We also concluded that with the updated time series that an upward trend in extreme variability was starting to appear.
Here we update the original time series through 2009 as shown in Figures 1a,b,c which show the percentage of the Northern Hemisphere extratropics affected by 2.0, 3.0, and 3.5 SD anomalies, respectively. There is now a clear and significant upward trend in the most extreme variability (Table 1) with the summer of 2008 being the most extreme yet. This is due to very large warm anomalies in northeastern Canada, around Greenland, and also in Siberia (Figure 2). Interestingly, these extremes in SD exceeded are largest in the near-surface layers of the atmosphere than in the mid-troposphere despite the temperature variability at high latitudes being much larger near the surface than in the mid troposphere (e.g., Peixoto and Oort, 1992; Figure 7.8) again suggesting that surface processes are more responsible than generalized climate warming.
Massive Arctic sea ice melt was likely one component of the unusual near-surface climate in Canada, the Labrador/Baffin Seas, and Greenland.
Figure 1. Histograms of percentage of the Northern Hemisphere from 22-80°N covered by thickness temperature anomalies exceeding 2.0, 3.0, and 3.5 standard deviations, respectively. Cold anomalies are in dashed lines, warm anomalies in solid lines. Note the different vertical scales.
Figure 2. Thickness temperature anomalies 1000-500 mb for JJA 2008 (color shaded) and standard deviations exceeded (2.0, 3.0, 3.5, 4.0 SD) contoured.
Figure 3. Major Northern Hemisphere warm temperature anomalies by pressure level: 68°W, 57°N is the eastern Canada Greenland anomaly, 140°E, 63°N is the Siberian anomaly, 73°E, 35°N is the central Asia anomaly.
|SD Exceeded||Slope (%/year)||P-Value|
|3.5 warm||0.003 (3 data points)||0.06|
Table 1: Slopes and P-values for linear regressions for time series in Figure 1 and for 2.0 SD cold anomalies (not pictured in Figure 1). Higher-order cold anomalies are data sparse and are not given. 3.5 warm anomalies are also data sparse and not reliable (3 values) and are given only for completeness.
Chase, T. N., K. Wolter, R. A. Pielke, Sr., and I. Rasool, 2008. Reply to comment by W. M. Connolley on; Was the 2003 European summer heat wave unusual in a global context? Geophys. Res. Lett., 35, L02704, doi:10.1029/2007GL031574.
Chase, T. N., K. Wolter, R. A. Pielke, Sr., and I. Rasool, 2006. Was the 2003 European summer heat wave unusual in a global context? Geophys. Res. Lett., 33, L23709, doi:10.1029/2006GL027470.
Connelly, W.M., 2008. Comment on: “Was the 2003 European summer heat wave unusual in a global context?” Geophys. Res. Lett., 35, L02703, doi: 10.1029/2007GL031171.
Peixoto, J. P., and A.H Oort, 1992. Physics of Climate. American Institute of Physics. New York.