Day-to-day weather conditions have become more erratic in the past generation, say Princeton University researchers, with significant fluctuations in sunshine and rainfall affecting more than a third of the planet.
Extremely sunny or cloudy days are more common than in the early 1980s, and swings from thunderstorms to dry days have risen considerably since the late 1990s.
These swings could have consequences for ecosystem stability and the control of pests and diseases, as well as for industries such as agriculture and solar-energy production, says the team.
Existing climate-change models have been evaluated against the average weather per month – but this approach hides variability, says David Medvigy.
“Monthly averages reflect a misty world that is a little rainy and cloudy every day. That is very different from the weather of our actual world, where some days are very sunny and dry,” he says.
Equatorial Africa and Asia experienced the greatest increase in extreme conditions, with erratic shifts in weather occurring throughout the year. In more temperate regions such as the US, there was less day-to-day variability, and it was generally only seasonal. In the north-east of the country, for example, sudden jumps from sunny to bleak days became more common during the winter from 1984 to 2007.
The findings have important implications for future climate models, says Medvigy, and could make climate change worse.
“We have not yet looked for direct ties between weather variability and increased carbon dioxide concentration in the atmosphere, but I would not be surprised if they are connected in some way,” he says.
“Increases in variability diminish the efficiency with which plants and trees remove carbon dioxide from the air. All of a sudden, the land and the atmosphere are no longer in balance, and plants cannot absorb levels of carbon dioxide proportional to the concentrations in the environment. That will affect everybody.”