The extreme weather

"Just as dawn began to glow, there arose from the horizon a black cloud.... All day long the South Wind blew..., blowing fast, submerging the mountain in water, overwhelming the people like an attack. No-one could see his fellow, they could not recognize each other in the torrent.... Six days and seven nights came the wind and flood, the storm flattening the land. When the seventh day arrived, the storm was pounding, the flood was a war, struggling with itself like a woman writhing in labour. The sea calmed, fell still, the whirlwind and flood stopped up. I looked around all day long; quiet had set in, and all the human beings had turned to clay. The terrain was as flat as a roof. I opened a vent and fresh air, daylight, fell upon the side of my nose. I fell to my knees and sat weeping, tears streaming down the side of my nose."

―Gilgamesh XI:96–137 [1]

"[Hail] fell and lightning flashed back and forth. It was the worst storm in all the land of Egypt since it had become a nation. Throughout Egypt hail struck everything in the fields―both men and animals; it beat down everything growing in the fields and stripped every tree."

―Exodus 9:24 (NIV)

Extreme weather phenomena, however you define them, have been happening throughout mankind's memory. During the last decade, we have been told by the media that such events are increasing in frequency or that they are becoming more intense, and after each catastrophic storm the word goes that the storm was because of man-made global warming. It has been implied, for example, that Hurricane Katrina has been the result of man-made climate change [2]. There are two claims involved here: (a) that extreme weather events are increasing or intensifying; and (b) that this is the result of man-made global warming. Let's examine these claims.

We live in Athens, Greece, and the most extreme events we remember witnessing are a 10-day-long heat wave of 45°C (113°F) in the summer of 1987; an extremely cold winter in 1986–1987; and intense rainfall and flooding, which resulted in several deaths, in November 1977. More recent incidents, as far as we can remember, have been less marked, and therefore, as everyday casual observers rather than as scientists, we don't see any evidence that extreme weather events in Athens have increased. Our subjective experience of Athens may of course be different than your subjective experience of New Orleans or of wherever you happen to be living; but if you infer that extreme weather events are increasing because you witnessed Katrina, we could also infer that extreme weather events are decreasing because we live in Athens. What each of us has personally witnessed could well be random.

But then what about the huge number of extreme weather events that you have not witnessed and have been brought to your home by the media? Well, you'll never hear in the news that the weather in Greece is perfectly normal, because this is not news. You might be interested in learning that a famine has struck some place in the world, but you'd be quited bored to be told the list of countries whose diet remains unaffected. It is reasonable, therefore, for the media to transmit pictures of extreme weather from around the world, from places which may not make weather news again for a century. As much as it is debatable whether the extreme events have changed in the last few decades, it is beyond doubt that the penetration of the media into the remotest locations of the planet has increased dramatically.

Our subjective impressions of such events, whether we witnessed them or learned them from the media, are therefore of no help. We need to be more scientific: we need to define what we mean by extreme weather phenomena and count all such phenomena of a given large enough period. Figure 1 shows, for example, the number of major Atlantic hurricanes per 5 year period from 1946 to 2005; and although this has been increasing from 1990 to 2005 (and appears to be falling since, which is not visible in Figure 1), it doesn't look like anything really unprecedented. Note, also, that this is only the Atlantic: elsewhere things could have been different, and, indeed, the frequency of occurrence of cyclones and typhoons in China seems to be decreasing [3]. When researching such frequency globally, nothing is found that suggests any significant connection with global warming [4]. Other research indicates that, while the number of hurricanes may be nothing special, there is an unprecedented increase in their intensity [6]; however, that research is debated ([7], [8]).


Figure 1: Number of category 3–5 Atlantic hurricanes [5]

As in the case with the melting ice, our aim here is only to show that there is nothing nearly as alarming as advertised about extreme weather events. It is media penetration that causes us the impression of dramatic increase in such events. In reality, there is some change, but it is not surprising and not unprecedented; and since it is not unprecedented, it does not constitute any evidence of man-made global warming. What causes it? We'll come back to this question in the epilogue.

Next: The changing climate


[1]Available at, accessed on 2009-04-19.
[2]Pielke, R. A., Future economic damage from tropical cyclones: sensitivities to societal and climate changes, Philosophical transactions of the Royal Society 365, 2717–2729, doi: 10.1098/rsta.2007.2086, 2007; available at, accessed on 2009-11-10.
[3]Fumin Ren et al., Changes in tropical cyclone precipitation over China, Geophysical Research Letters 33, L20702, doi:10.1029/2006GL027951, 2006.
[4]P. J. Webster et al., Changes in tropical cyclone number, duration, and intensity in a warming environment, Science 309 (5742), 1844–1846, doi: 10.1126/science.1116448, 2005.
[5], accessed on 2009-08-06.
[6]Kerry Emanuel, Increasing destructiveness of tropical cyclones over the past 30 years, Nature 436, doi:10.1038/nature03906, 2005.
[7]Roger A. Pielke, Jr, Are there trends in hurricane destruction?, Nature 438, doi:10.1038/nature04426, 2005.
[8]Christopher W. Landsea, Hurricanes and global warming, Nature 438, doi:10.1038/nature04477, 2005.