The Summer Heat Wave of 2003: A Signal of Climate Change?

The summer heat wave in southern and central Europe may have been more extreme and improbable than the many heat records and the strong droughts have first indicated.

New investigations show that the weather in the summer 2003 may have been a taste of a climate that we are going to face in the future.

Hard to Explain

Even when considering the general warming that has taken place during the last 150 years (a bit less than 1 degree Celsius in Europe), it is very difficult to explain the extreme heat of this summer as a consequence of natural climate variations.

The summer of 2003, however, is not particularly unusual if one compares it to simulations of the future climate towards the end of the century, as a result of man-made greenhouse gas emissions that affect our climate system.

As part of the Prudence project, Prof. Christoph Schär from the Institute for Atmospheric and Climate Science at ETH-Zürich, and his colleagues have analyzed simulations from the project. Their results have been published recently in Nature (427, pp. 332-336, 2004, view abstract and download paper or ask for reprint).

The Temperature Rises

The analysis shows that we should not only expect higher average temperatures, but in many places also a significantly increased year-to-year variability during the summer seasons. Observations show that the temperature has increased over the previous 150 years, but an increase in variability has not yet been detected.

Very Rare, or a Glimpse of the Future?

According to the new investigations by Christoph Schär and coworkers, this summer was either an extremely rare event, or a taste of new climatic conditions to come, or a combination of the two. The anticipated increase in variability might make the adaption to warmer climatic conditions even more challenging than previously expected.

Simulated change in average summer temperature (upper panel) and in interannual variability (lower paned) from the period 1961-1990 to the period 2071-2100.