March 9, 2004

European Hotties

Filed under: Health Effects, Heat Waves

Summer 2003 may or may not have been Western Europe’s hottest on record. But Europeans should have seen it coming and adapted as Americans have.

Whether or not the summer of 2003 was the hottest on record in Western Europe we may never know. But the heat itself should not have taken Europeans by surprise.

The original research on seasonal temperature changes appeared in the March 5 issue of Science. After reconstructing Western Europe’s seasonal temperature history since the year 1500, a team of Swiss climate scientists headed by Jurg Lauterbacher concluded that summer 2003 was the warmest since the beginning of their reconstruction; the second-warmest summer was about 250 years ago in 1757. (Interestingly, they also determined that winter 2002-2003 was below the average winter temperature of the 20th century, and that only two of the 25 coldest winters have occurred since 1950.)

As warm as 2003 was, probable errors in the early records should have led to a much softer conclusion about whether it was the all-time warmest ever. Yet once again, the reviewers at Science seem reluctant to temper their contributors’ overly strong statements about climate change. (World Climate Report recently discussed some obvious flaws in a 2002 Science paper on Mt. Kilimanjaro:

Figure 1 shows the reconstructed European summer temperatures since 1500, based upon thermometer records and temperature proxies. Thermometer records become increasingly sparse as the record goes back in time (there are none before 1659). “Proxy” records, such as tree rings, become more important in the early part of this history. Such records usually only capture between a quarter and a half of the true inter-summer temperature change, resulting in large potential errors. Lauterbacher et al. note these quite well, but don’t emphasize the uncertainty that proxy records impose—uncertainties that include whether one summer, 2003, was in fact hotter than any other in their reconstructed record.

European Summer Temperatures

Figure 1. Reconstructed European summer (June, July, August) temperature history since 1500 (from Luterbacher et al., 2004).

Notice that the record is characterized by large year-to-year variations (black line) occurring over a slowly varying 30-year average (red line). The blue lines represent the 95 percent confidence range for these three-decadal weighted averages, not the error expected in a given year, and, as noted below, these confidence ranges call into question their conclusions about 2003.

The summer history varies a great deal on decade-to-century scales. There was a rapid rise in average summer temperature in the early- to mid-18th century, for example, making many summers in the latter part of the 18th century and early portion of the 19th century warmer than recent ones (with the exception of 2003). A nearly two-century-long cooling trend then set in, resulting in summers in the early 20th century being the coldest of the past 500 years. During the past 100 years, temperatures have recovered from their 1902 low point.

The summer of 2003 proved to be very warm, but how does it actually compare with 1757? If the 30-year period encompassing that summer was actually near the top of the confidence limit (upper blue line), then 2003 and 1757 are indistinguishable. But why didn’t the authors give the error bars for an individual year? If the climatologists at World Climate Report were asked to review this paper, we surely would have told Science to insist on that calculation!

One hint that we are on to something here has to do with those blue lines, which, again, are based upon 30-year weighted averages. There are three consecutive centuries (1500 to 1800) in which the top (warmest) confidence limit exceeds the top of the confidence limit for any time in the entire 20th century. That makes the estimation of the true value for a given year problematical, to say the least, for the first 300 years, and renders the frank statement that 2003 was warmer than any other year the product of a little creative and perhaps wishful thinking. Such speculation should have been removed in the peer review process.

That quibbling aside—it was a hot summer—the Euros should have seen it coming. Average summer temperatures had been rising for the past three decades. So it was only a matter of time before natural variations led to an anomalously warm summer being superimposed on the already warm climate of the late 20th and early 21st centuries.

The summer of 2003 was particularly newsworthy, as the number of heat-related deaths in Europe soared with the temperatures. Significantly elevated heat wave mortality occurs in regions where extreme heat is rare. But those deaths didn’t occur in a 30-year vacuum.

Heat waves become increasingly common in a warming climate, and the more common they become, the more a society can adapt. They also become more frequent as our cities warm from the “urban heat island” effect, which happens whether or not there is global warming.

Take Chicago, for instance. During a heat wave in mid-July 1995, it is reported that there were more than 700 excess heat-related deaths. In July 1999, a heat wave of nearly identical character occurred resulted in little more than 100 excess deaths.

In only four years, the population of Chicago learned how to better deal with extreme heat, and reduced mortality by 86%. In 1999, the National Weather Service in Chicago issued heat wave warnings well in advance. Press releases reminded everyone of the 1995 death toll. “Cooling centers” were opened to the public throughout the city accessible via free bus service. And municipal workers and police officers checked on elderly residents. Those simple measures—adaptations made over a short period of time—saved literally hundreds of lives (Palecki et al., 2001).

(Of course, it’s worth noting that the 1995 heat wave killed several thousand less in Chicago than died in France in 2003. That’s because of the wide stateside availability of air-conditioning powered by relatively inexpensive electricity, two commodities made more cost-prohibitive by European energy policies).

Western Europe should respond similarly. Let’s assume they were caught off their guard by the heat in 2003, much the way Chicago was in 1995. And given that many scapegoated governmental officials lost their jobs over the lack of preparedness that led to the high mortality numbers, you can bet that next time around things will be different.

Can they be? W.R Keatinge, writing in a 2000 article in the British Medical Journal, concluded:

Populations in Europe have adjusted successfully to mean summer temperatures ranging from 13.5°C to 24.1°C and can be expected to adjust to global warming predicted for the next half-century with little sustained increase in heat-related mortality. Active measures to accelerate adjustment to hot weather could minimize temporary rise in heat related mortality, and measures to maintain protection against cold in winter could permit substantial reductions in overall mortality as temperatures rise.

There seems to be every reason to believe that if big heat becomes more commonplace in Europe in the coming centuries, people will pay far less a price for it than they did in 2003. The Chicago example provides evidence for the fact that the American Way—adapting to a warming climate—is far more efficacious than the Euro Way of trying to change its course.


Keatinge, W.R., et al., 2000. Heat related mortality in warm and cold regions of Europe: observational study. British Medical Journal, 321, 670–673.

Luterbacher, J., et al., 2004. European seasonal and annual temperature variability, trends, and extremes since 1500, Science, 303, 1499–1503.

Palecki, M.A., S.A. Changnon, and K.E. Kunkel, 2001. The nature and impacts of the July 1999 heat wave in the midwestern United States: Learning from the lessons of 1995, Bulletin of the American Meteorological Society, 82, 1353–1367.

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