How scientists linked the California drought to climate change

Editor’s note: This post was updated December 15, 2014.

California has officially entered its fourth consecutive year of drought, and is trapped in its worst water shortage situation ever.

Because we know that human-caused climate change can trigger and exacerbate drought conditions, media, public officials, California residents and scientists have all been wondering for years if rising global temperatures likely caused or contributed to the current drought in California.

The short answer: Yes, they did.

Weather won’t cooperate

Scientists have suspected for some time now that a certain meteorological condition lies behind the long-lasting California drought. The persistence of a stubborn high-pressure system off the coast has been preventing storm systems from reaching California and instead deflecting them to Alaska and elsewhere.

While weather events are almost always multi-causal, the California drought is largely a result of this atmospheric weather pattern. The question is whether climate change has influenced the development, or sustenance, of this system.

Stanford scientists connected the dots

When destructive events happen, people want to know right then and there what’s going on— whether it’s an epidemic, riot or weather disaster.

But evaluating an extreme weather event for climate change influences is a scientific process that takes several months of computer simulations and statistical techniques. It can frustrate some who demand an answer right away.

Well, the results from several, month-long studies are finally in. Scientists from Stanford have found that the meteorological conditions that have caused the California drought are far more likely to occur in today’s warming world than in one without human-caused emissions of greenhouse gases.

It shows us – ironically and tragically – that the state that leads the nation in curbing greenhouse gas emissions is right now suffering more than any other from climate change. 

California is not alone

The California drought attribution studies are a subset of a larger collection of recently published studies that explain 16 extreme weather and climate events of 2013.

Twenty research teams explored the causes of events such as heat waves in Australia, New Zealand, Korea, Japan, China, and Europe; torrential downpours in Colorado and India, a blizzard in South Dakota, and a cold spell in the United Kingdom.

The studies overwhelmingly indicated that all heat waves were largely attributable to human-caused climate change. One study even suggested that the heat wave in Korea has been made 10 times more likely due to human influence.

The extreme rainfall events in India were concluded to have been more likely in a human-influenced world, but data for assessing precipitation events is rather limited as compared to heat waves. Further, studies concluded that the extreme rainfall event in Colorado, the blizzard in South Dakota, and the cold spell in the U.K. were unlikely to have been influenced by climate change.

Climate change is happening. Now.

So for anyone who may still think that the consequences of climate change are in the distant future, this collection of studies suggest that human-caused climate change is right now causing a crisis in America’s most populous state and the world’s eighth largest economy.

California reminds us that climate change is a major concern for societies everywhere, and that all nations are vulnerable to extreme weather events. It’s time we roll up our sleeves and stop this, once and for all.

The following paragraphs were added after this blog post was initially published:

A growing body of research analyzing the California drought is providing a more comprehensive view of the current drought situation.

All extreme weather events, and especially droughts, occur as a result of multiple factors. Several research studies are therefore analyzing the contributing factors to the California drought to determine if they are natural or human-caused.

The collective results from five studies thus far suggest that:

• this is the most severe drought in the last 1,200 years.
• record-warm temperatures have exacerbated the drought. 
• it’s not part of a long-term change in precipitation.
• the high-pressure ridge sustaining the drought is much more likely to occur with man-made climate change.
• sea surface temperatures influence the development of a ridge.
• La Niña, a natural climate cycle, has contributed to recent sea surface temperatures.

There is evidence, in other words, that the California drought is caused by a combination of natural and human factors.