Climate change link to global droughts goes back a century, study finds
Humans have contributed to increased global risks of drought for more than a century, scientists say, in findings that also point to “severe” consequences ahead with climate change.
The research by US-based scientists and published in Nature journal on Thursday comes as the latest Bureau of Meteorology data showed the first four months of 2019 were the hottest on record for Australia as drought tightened its grip on the country’s south-east.
The scientists, led by Kate Marvel at NASA’s Goddard Institute for Space Studies, used so-called drought atlases derived from tree-ring data combined with satellite observations and climate models to identify how soil moisture has changed.
They found drought increased during the first half of the 20th century, eased in the quarter century to 1975 and worsened again. The pause in the trend coincided with increased aerosol pollution.
“Models project and observations show a re-emerging greenhouse gas signal towards the end of the 20th century, and this signal is likely to grow stronger in the next several decades,” the paper concluded. “The human consequences of this, particularly drying over large parts of North America and Eurasia, are likely to be severe.”
Paul Durack, a research scientist and an author of the paper, said the study was the first to show global-scale droughts to be impacted by human activities.
“This is potentially bad news for Australia, and similar climate regions such as California,” he said in a statement. “These regions have experienced devastating recent droughts, and if the model projected changes continue, such droughts will become more commonplace into the future.”
Andrew King, climate extremes research fellow at the ARC Centre of Excellence for Climate System Science, said while heat extremes caused by climate change have been clear, “droughts are very complicated”, with natural variability masking the trends, Dr King said.
“You’d expect the signal to be weaker. Like in this study, we found an increased human fingerprint for heat extremes more recently that will continue to increase in the next few decades.”
Hot start to 2019
Day-time readings, for instance, beat the previous record set only a year earlier by almost half a degree, coming in at 1.93 degrees above the 1961-90 average.
Rain is slightly more than a quarter below average nationally.
Regions such as the Murray-Darling Basin were also the hottest on record for mean temperatures, with rainfall this year slightly below half the norm – although rains later this week should help.
Sydney is tracking the hottest on record for daytime temperatures – averaging 27.2 degrees so far in 2019, or 2.4 degrees above average. Rainfall is about a 22 per cent below the norm.
NSW is also enduring its hottest start to any year for mean temperatures. The 2.79-degree anomaly eclipsed the previous record departure of 2.51 degrees from the 1961-90 average set only in 2018, the bureau said. Rainfall is running at 55 per cent below the average for the fourth-driest start to a year.
For Victoria, mean and minimum temperatures were the warmest on record for the January-April period, and daytime readings were second only to the same period in 2018. Rainfall is about 44 per cent below average.
Most Melbourne sites have also been tracking their hottest starts to any year, while many locations are also having their driest January-April periods, the bureau said.
Originally published by The Sydney Morning Herald, 2 May 2019.