In a study entitled “Twentieth-century hydroclimate changes consistent with human influence” published recently in the journal Nature, scientists claim they have detected evidence that human activity has contributed to drought conditions in many parts of the world beginning as early as the early 1900s.
A common theme among climate scientists is that in a warming world, dry parts of the planet will become drier and wet parts of the planet will become wetter. Some of the areas identified as subject to increasing dryness are major agricultural zones. The implication is that more drought conditions could lead to famine in many parts of the world.
“Climate change isn’t a new thing,” Kate Marvel, a climate scientist at the NASA Goddard Institute for Space Studies and Columbia University, tells the New York Times. Marvel is the lead author of the report, which connects anthropogenic climate change to the history of drought events for the first time.
Using new computer modeling tools, the researchers took data derived from tree rings and correlated that information with long term patterns of moisture levels in soil in North America, Central America, Eurasia and the Mediterranean. The tree ring data “give us a record of global drought going back centuries,” Marvel says.
Finding A Background Note In A Symphony
She is quick to point out that “we’re not saying we’re seeing a large effect” in the historical record. Instead, the research teases out the effect of human activity from the natural background variability of weather and climate, “a background note against a symphony of other sounds,” she says. Benjamin Cook of the Goddard Institute and Columbia University and a co-author of the study, adds that “we’re beginning to understand the fundamental processes and the basic impact of climate change on drought.”
Many people confuse weather and climate. Weather is what is happening outside the window right now. Climate is what has happened outside the window for the past century or so. To tease that “background note” out of the data, the researchers focused on three regions — Australia, Mexico, and the Mediterranean.
They found they all exhibited evidence of drier soil at the same time even though they react very differently to weather phenomena like El Niño. “This means that it is harder for natural climate variability alone to produce, by chance, the simultaneous drying across all three regions identified in the fingerprint. The human consequences of this, particularly drying over large parts of North America and Eurasia, will likely be severe,” the authors warn.
A Mid Century Anomaly
The research revealed some unexpected results. For the first half of the 20th century, the data suggests a strong correlation between drought and human activity. But from 1950 through 1975, there was a decrease in global drought. Then the trend toward drier conditions picked up again and has accelerated in the first part of the current century.
The scientists theorize that aerosol pollutants like oxides of sulfur that contribute to smog actually blocked some of the sun’s light from reaching Earth, which had a corresponding effect on weather patterns. Once nations began taking such atmospheric pollution seriously and devised ways to lower the amount of pollution in the air, the trend toward drought conditions picked up speed.
“It was kind of an accidental geoengineering experiment in the middle of the 20th century,” Dr. Cook says. That is not an endorsement of such geoengineering, however. Dirty air is dirty air. Human lungs prefer clean air. Filling the atmosphere with pollutants presents a Hobson’s Choice that is really no choice at all. Far better to eliminate the pollution caused by burning fossil fuels in the first place rather than putting more junk into the air to mask the effects of the junk that is already there.
Friederike Otto, acting director of the Environmental Change Institute at the University of Oxford, tells the Times in an e-mail the study is important because it shows “climate change is really here and happening now and not something we can afford (in all meanings of that term) to continue to ignore.”
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