麻豆传媒

DROUGHTS around the world dating to the early 20th century may have been made worse by greenhouse gas emissions.

Scientists have previously hesitated to draw links between global warming and drought, due to a lack of observational data and the difficulty of distinguishing natural cycles of dry conditions from ones that are driven by climate change.

But Kate Marvel at the University of Columbia in New York and her colleagues have found that the impact of greenhouse gas emissions on drought was clearly visible between 1900 and 1949 (Nature, ).

鈥淐limate change is not a recent phenomenon,鈥� she says. 鈥淲e鈥檝e known about it for a long time, and it鈥檚 actually been happening for a long time.鈥�

By comparing climate models that can account for the impact of emissions on drought with tree ring, rainfall and temperature records, her team found clear evidence that human activity influenced droughts during the first half of the 20th century. But between 1950 and 1975, there was no evidence of an effect.

鈥淐limate change is not a recent phenomenon, it has actually been happening for a long time鈥�

The discrepancy is explained by another human impact that had a cooling effect 鈥� the amount of aerosols we released by burning huge amounts of coal, along with other industrial activities. 鈥淲e put a bunch of junk in the atmosphere that blocks the sun,鈥� says Marvel.

From 1981 to 2017, there were signs of a link, but not enough to say unequivocally that droughts were influenced by human-induced climate change rather than by natural variations.

That might sound odd, given that this period coincides with a large rise in greenhouse gas emissions. Marvel and her team are still examining possible explanations for this. One is that aerosols have declined but may still be playing a role.

However, the researchers expect the link between carbon emissions and drought to become increasingly clear in the coming decades. 鈥淭he impact of climate change [on drought] should be indisputable by the middle of the century,鈥� says Marvel.

The drying effect will not be uniform across the world 鈥� while many places are expected to get drier, some are anticipated to get wetter 鈥� but it is expected to have severe consequences for people.

The research isn鈥檛 able to blame individual drought events, such as the US Dust Bowl of the 1930s, on our emissions. 鈥淭he signal [of the human fingerprint] is really only detectable when you look at a global picture,鈥� says Marvel.

She hopes the new work will enhance the credibility of climate models and their ability to anticipate the impact of future droughts.