Recent News

A recent study pub­lished in the jour­nal Nature, reveals that man-made green­house gases have been a cause of drought for more than a cen­tury.

As part of the study, sci­en­tists at Columbia University’s Earth Institute stud­ied recon­struc­tions of the Palmer Drought Severity Index, which uses infor­ma­tion on tem­per­a­ture and pre­cip­i­ta­tion to esti­mate rel­a­tive dry­ness and quan­tify drought, and com­pared these with data from 600 to 900-year-old tree rings.

The tree rings were used as a base­line to exam­ine weather pat­terns before they were affected by human activ­ity in the form of the cre­ation of green­house gases. Both sets of data showed sim­i­lar drought pat­terns and on this basis, con­clu­sions revealed a clear sign of the human influ­ence on green­house gases.

By study­ing cli­mate models, the sci­en­tists iden­ti­fied three dis­tinct peri­ods. During the first half of the cen­tury from 1900 to 1949, the study notes that signs of the effects of global warm­ing due to the pro­duc­tion of green­house gases were already obvi­ous.

“The big thing we learned is that cli­mate change started affect­ing global pat­terns of drought in the early twen­ti­eth cen­tury,” Benjamin Cook, the study’s co-author, said. “We expect this pat­tern to keep emerg­ing as cli­mate change con­tin­ues.”

The period from 1950 to 1975 was marked by a “global increase in aerosol forc­ing.” During this time, the use of large amounts of indus­trial aerosols reached a peak and affected cloud for­ma­tion, pre­cip­i­ta­tion and tem­per­a­tures. Also during this period, the amount of green­house gases in the atmos­phere rose, but this may have been masked by the effects of aerosols.

In more recent years, from 1981 to the present, the study notes that “the signal of green­house gas forc­ing is present but not yet detectable at high con­fi­dence.”

Though there has been a decrease in the use of aerosol pol­lu­tion in the past decades, indus­trial activ­i­ties have increased and resulted in rising emis­sions and tem­per­a­tures. The effects of cli­mate change on the hydro­cli­mate have been espe­cially obvi­ous since 2000.

“It’s mind bog­gling,” lead author Kate Marvel said. “There is a really clear signal of the effects of human green­house gases on the hydro­cli­mate.”

According to the con­clu­sions drawn from the researchers’ obser­va­tions, there is an increased drying of soil hap­pen­ing in much of North America, Central America, Eurasia and the Mediterranean, while the Indian sub­con­ti­nent has become wetter.

As for drought pre­dic­tions for the near future, the out­look is bleak. The study pre­dicts a period of unprece­dented drying in many parts of the world, par­tic­u­larly in areas of North American and Eurasia where this may even be severe. Some of the world’s agri­cul­tural areas are at risk of drying out and can even become per­ma­nently arid. These trends are likely to have neg­a­tive reper­cus­sions on the human pop­u­la­tion.

As for pre­cip­i­ta­tion, fore­casts pre­dict the same or an increased amount of rain­fall in Central America, Mexico, the cen­tral and west­ern United States and Europe in the years to come. But at the same time tem­per­a­tures are expected to rise and result in more evap­o­ra­tion of mois­ture from the soil in these areas of the world.

The Mediterranean region is expected to receive less rain­fall and more evap­o­ra­tion due to heat. More rain is pre­dicted for the Indian sub­con­ti­nent because of the warm­ing of the Pacific and Indian Oceans, but rain­fall pat­terns may be unpre­dictable and storms more likely.

• Earth Institute, Columbia University


• Nature


• National Geographic