"The conditions we've had for the past five years – very very high temperatures and relatively low precipitation – that could well be the way that we'll see out the 21st century," said Glen MacDonald, who authored the study. "Our research suggests that in the past when we've had prolonged periods of warm temperatures, like we're experiencing in the 21st century. They tend to coincide in California with long periods of aridity."

In the past, those long periods of warming and drying were associated with natural phenomenon including changes in the Earth's orbit, in volcanic activity and in the output of the sun. But there's a new factor influencing temperature levels around the planet: greenhouse gases.

MacDonald said that according to current models, the increase in greenhouse gasses is contributing 15  to 25 percent to the severity of the current drought in California.

These gases are trapped in the upper atmosphere and act as a sort of giant blanket that contribute to something called radiative forcing. Basically, that's when energy from the sun gets trapped and heats up the Earth, instead of bouncing back into space.

To figure out California's arid history, MacDonald and his team compared sediment samples from a lake in the Sierra Nevada mountains with sediment samples from the Pacific. By comparing the relationship between the samples they were able to discover a connection between a warming earth, ocean temperature shifts and long stretches of a very dry California. Or, in other words, the same conditions that we're seeing nowadays.

"Based on our study it could be quite possible that as we move into the 21st century that the conditions we've seen over the last five years, these will be more or less what normal conditions are like," said MacDonald. "And then on top of that we would have more severe drought and that drought could last for longer periods. 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... This might not be a three to five year thing."

If you'd like to hear more about the study click on the audio at the original story HERE

by Jacob Margolis | Take TwoSeptember 15 2016

source: http://www.scpr.org

original story HERE

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