In an unusual new study, scientists say they have detected the fingerprint of human-driven global warming on patterns of drought and moisture across the world as far back as 1900.
In an unusual new study, scientists say they have detected the fingerprint of human-driven global warming on patterns of drought and moisture across the world as far back as 1900. Rising temperatures are well documented back at least that far, but this is the first time researchers have identified resulting long-term global effects on the water supplies that feed crops and cities. Among the observations, the researchers documented drying of soils across much of populous North America, central America, Eurasia and the Mediterranean. Other areas, including the Indian subcontinent, have become wetter. They say the trends will continue, with severe consequences for humans. The study appears this week in the leading journalNature.
In general, scientists agree that as global warming progresses, many now dry regions will become drier, and wet ones will become wetter. Some recent studies suggest that human-induced warming has intensified droughts in particular regions, including a now near 20-year ongoing drought in the southwestern United States. However, the last report by the Intergovernmental Panel on Climate Change says confidence in attributing specific ongoing events directly to humans is still chancy.
The new study combines computer models with long-term observations to suggest that systemic changes in what scientists call the hydroclimate are already underway across the world, and have been for some time. The researchers looked not simply at precipitation, but rather soil moisture, a more subtle measure that balances precipitation against evaporation, and is the quality most directly relevant to farming and forestry. They used tree rings going back 600 to 900 years to estimate soil moisture trends before human-produced greenhouse gases started rising, then compared this data with 20th-century tree rings and modern instrumental observations, to see if they could pick out drought patterns matching those predicted by computer models, amid the noise of natural yearly or decadal regional weather variations.
Read more at The Earth Institute - Columbia University
