Two strikes, and you're out

Climate change looks set to increase the rates of lightning strikes, a new study has shown...

Worldwide there are more than 2000 thunderstorms occurring at any one moment, zapping the Earth below roughly 100 times per second. These discharges, which each dissipate between one and ten billion joules of energy - the equivalent of a quarter of a tonne of TNT - contribute to the composition of the atmosphere by triggering chemicals reactions between oxygen and nitrogen.

Lightning strikes also cause fires. In fact, half of the wildfires reported in the US are attributed to lightning strikes, and every year there are human victims. Now new research suggests that climate change could intensify the intensity and frequency of thunderstorms by at least 12% per degree of temperature rise. Put another way, according to University of California, Berkeley, scientist David Romps and his colleagues in their paper in Science this week, for every two strikes in the year 2000 there will be three in 2100.

The Berkeley team reached their conclusions by using data from a large network of sensors across the US mainland which can pick up radio pulses produced by lightning strikes and localise them geographically. These strike data were then married up with co-existent atmospheric temperature and precipitation measurements for each place.

Higher temperatures mean more convective power, while water-saturated air supplies the ice crystals - or hydrometeors - that rub together to "charge up" thunder clouds. The product of the two, the researchers found, is strongly correlated with lightning frequency. This means that temperature changes anticipated through the effects of climate change are likely to increase the overall strike frequency.

A further complexity is that lightning itself modifies the atmosphere, producing oxides of nitrogen. These are themselves greenhouse gases, which are likely to accelerate the process yet further. Applying the results to 11 different climate models suggests that lightning strikes are likely to become 50% more frequent by the end of the century, alongside all of their attendant risks...