Climate Change Vs. the Blob

A new study says a stubborn blob of warm ocean water is exacerbating the California drought.

April 14, 2015

What’s causing the California drought? Melting Arctic ice, a high-pressure ridge, and La Niña have all been blamed, but my favorite theory emerged last week—the blob.

For those who missed out on the 1958 trash masterpiece and Steve McQueen vehicle, The Blob told the story of a man-eating slime wad that terrorized humankind with its size and persistence. The new California drought theory is basically the same thing, minus the slime. The idea is that a massive column of warm water, 300 feet deep and 1,000 miles across, has been occupying more or less the same location in the Pacific Ocean for more than two years. The warm spot changes shape occasionally and has drifted closer to the West Coast, but its most dangerous feature is its ability to stubbornly dominate a large space.

It’s not entirely accurate to say the blob caused the California drought, as many stories have strongly implied. In fact, the blob is part of a complex system—a sort of meteorological Rube Goldberg machine—that has fostered and sustained the state’s historic dryness.

According to the National Oceanic and Atmospheric Administration, the problems started with the ocean-atmosphere interaction known as La Niña, which parked a high-pressure system just off of the West Coast in 2011. That high-pressure system had several effects. First, it rerouted storms that were heading toward the western United States, depriving California and the West of precipitation. It also changed the direction of the winds passing over the Pacific, diverting cold air that normally absorbs heat from the ocean. Hence, a warm ocean blob emerged.

Photo: NOAASea surface temperature anomaly off the coast of Washington and Oregon for April 2014, compared to 1981-2010.

Since the blob is between two and seven degrees Fahrenheit warmer than normal for that part of the Pacific, the air passing over the ocean to the land is unusually warm as well and is therefore less likely to produce snowfall. Reduced snowpack has been one of the primary aggravators of the California drought. Governor Jerry Brown made this point earlier this month, when he announced water use restrictions while standing on a patch of brown Sierra Nevada grass that would have been buried under five feet of snow in an average year.

What about climate change? Even in a story about a blob, climate change is the elephant in the room. You can’t write a weather story without it. The problem is that climatologists don’t yet agree on what role it has played in the California drought, if any. At the end of December, NOAA released a study that attributed the drought to “natural variability,” which has become a popular way of saying “not climate change.” The theories discussed above—La Niña, the high-pressure ridge, and the blob—are part of that natural variability explanation. Those phenomena existed before anthropogenic climate change began to strongly influence weather systems.

Several prominent climatologists dispute NOAA’s assessment to varying degrees. In February 2014, John P. Holdren, President Obama’s senior science director, wrote an interesting (and accessible) essay arguing that climate change should be considered one of the drought’s major contributors. Holdren made three central points. First, climate change has concentrated global precipitation into a smaller number of major storms, which results in runoff rather than the absorption of water into the ground. Global warming has also increased the elevation at which rain switches to snow, diminishing snowpack and therefore decreasing the volume of streams in spring and summer. Finally, warmer temperatures accelerate evaporation, which dries out the soil. You can think of these as narrow technical disagreements with NOAA’s natural variability explanation.

A bigger challenge to NOAA’s case comes from Lisa Sloan, a professor of earth sciences at the University of California, Santa Cruz, who predicted more than a decade ago that melting Arctic ice would cause the ocean to pass more heat to the atmosphere, which would change the path of storms over North America. Her 2004 study was titled, with alarming prescience, “Disappearing Arctic sea ice reduces available water in the American West.” Sloan’s theory is that climate change is behind the high-pressure system that is blocking the path of storms to the West. Essentially, she argues that NOAA hasn’t looked back far enough. (For a full explanation and some thoughts on Sloan’s theory from prominent climatologists, see Joe Romm’s excellent 2014 article in ThinkProgress.)

It will likely take several more years before we know with certainty whether and how climate change—or, for that matter, the blob—contributed to the California’s current drought. But even those who don’t blame climate change, such as Washington State climatologist and blob study author Nick Bond, say the drought is a dress rehearsal for what climate change could soon bring.

“We expect [droughts] to happen more frequently in future decades as part of global warming,” says Bond. “This is an opportunity to see what parts of the system are going to see big changes, and which are better at shrugging off this sort of thing.”

In the meantime, run—don’t walk—from fossil fuels. 

onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

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