Cyclones and climate change: The new normal? WAS typhoon Haiyan the strongest recorded storm to make landfall? Meteorologists will never know. Reliable records go back only a few decades. But it is surely one of them. Besides the devastation and the death toll, one way to assess its potency is to compare it with Katrina, the hurricane that devastated New Orleans in 2005. At its most intense, Haiyan's peak wind speeds were probably greater than 300kph (190mph). The best estimate for Katrina, when it hit land, is around 200kph. Regardless of its precise position in the historical hierarchy, Haiyan - like Katrina - has provoked discussion about the effects of global warming on tropical storms. Naderev Sano, the Philippines" representative at a climate summit in Warsaw, was unequivocal, daring doubters to visit his homeland. "The trend we now see is that more destructive storms will be the new norm," he said. In theory, a warmer world should indeed produce more potent cyclones. Such storms are fuelled by evaporation from the ocean. Warmer water means faster evaporation, which means more energy to power the storm. A warmer atmosphere can hold more moisture, which means more rain. But other factors complicate things. Tropical cyclones cannot form when wind speeds in the upper and lower atmosphere differ too much. Climate models suggest, in the North Atlantic at least, that such divergent winds may be more common in a warmer world. The Intergovernmental Panel on Climate Change (IPCC) reckons that the frequency of cyclones will stay the same or decrease while their average intensity goes up. That is the forecast. But the evidence so far is messy. Meteorological records are of uneven quality, and tropical storms vary widely in intensity, which makes spotting trends tricky. One potent storm from 1979, Typhoon Tip, holds the record for the lowest atmospheric pressure recorded, another measure of a storm's intensity. Yet levels of carbon dioxide, the main greenhouse gas, were only 337 parts per million (ppm) in 1979, compared with 394ppm in 2012. The IPCC concludes that, although there is good evidence for more and stronger Atlantic hurricanes over the past 40 years, there is no consensus on the cause of them. Worldwide, there is no trend in either the frequency or the intensity of tropical storms. And, given the rarity of such storms as Typhoon Haiyan, it will take a long time for any trend to become apparent.