And not only has climate change been at the forefront of California’s five-year drought, it may also increase the chances of further droughts, and change things in a similar fashion to historic, non-man-made climate change. But in modern times, those have been joined by a new force: greenhouse gases generated by the burning of fossil fuels and other human sources.
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The U.S. Forest Service in June said a combination of drought, a bark beetle infestation and hotter temperatures killed an estimated 66 million trees in California’s forests of the Sierra Nevada over the last six years.
The study, published today in the journal Scientific Reports, looked at the history of California’s dry periods over the past 10,000 years.
In findings consistent with previous research, the study found that past periods of drought in the American West, such as those that occurred between 5,000 and 1,000 BC and during the European Middle Ages, aligned with climate warming and cool ocean temperatures in the eastern Pacific Ocean.
“Radiative forcing in the past appears to have had catastrophic effects in extending droughts”, said MacDonald, an global expert on drought and climate change, in a statement.
Investigating this issue, scientists from UCLA have analysed lake sediment record from the Holocene era, as well as marine sediment records from the Pacific.
Essentially, the drought lasts as long as whatever is causing the radiative forcing is present. Recently, the increase of greenhouse gases in the atmosphere has been added to the mix, and it is now the major factor increasing the risk of aridity persisting in the region.
In a press statement, the study authors said that their data offers proof of a “persistent relationship” between earlier climate change events, Pacific sea surface temperature shifts, and previous aridity events in California.
“We suspected we would see the millennia of aridity during the mid-Holocene at Kirman Lake, but we were surprised to see a very clear record of the medieval climate anomaly as well”, says MacDonald. Since greenhouse gases are unlikely to be reduced quickly, it is likely that the conditions for aridity will remain intact in California. We’re used to thinking next year the drought’s going to end or it’s going to end after two years or three years. So, with the increasing number of greenhouse gasses, California could be preparing for many centuries of drought.
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MacDonald concluded that the temperatures in California are expected to increase, the lakes would get shallower while snowfall and rainfall would significantly decrease.
