Rising Ocean Temperatures Could Mean a Very Hot Summer

Weather conditions are stacking up to make 2015 a remarkably hot year for much of the United States. Could it beat 2014 as the hottest in recorded history?

Last month, the waters off California, Oregon, and Washington were about 1.8 to to almost 5.4 degrees Fahrenheit warmer than the historical average, according to data released Monday by the National Oceanic and Atmospheric Administration.

These sea surface temperatures are part of a lengthy natural cycle called the Pacific Decadal Oscillation, said meteorologist Steven Di Martino. The longer they remain above-average warm, the hotter the temperatures on land are likely to be.

But they have come on top of recent, record-setting warm terrestrial temperatures, which many have credited to human-caused climate change and which prevented snowpack from piling up in the mountains of California, Oregon, and Washington during the winter.

Melting snowpack provides a great deal of the summer freshwater supply in these states, particularly for river and stream flows that are important to salmon runs as well as hydropower supplies. California, for instance, faces severe water shortages as its snowpack is just 6 percent of normal, depriving cities and farms of desperately needed water.

NOAA’s data also confirmed that warmer-than-average sea surface and near-surface ocean temperatures have formed in the Eastern Pacific, creating a stretch of warmer water from Indonesia to California. It’s part of the El Niño period that began last year.

El Niño years occur when higher sea-surface temperatures combine with atmospheric conditions to create warmer waters across the equatorial Pacific. The reverse of the cycle, when sea-surface temperatures are cooler than average, is called La Niña.

El Niño periods can bring additional rain to the West Coast. But “what California wants to break its drought is a strong, East-based El Niño,” said Di Martino, while this El Niño is weak, with warm waters focused in the Western Pacific.

“This will focus a lot of moisture on Baja California and Texas rather than on California,” he said, and is “likely to bring a cooler than normal summer to the Northeast, with a lot of thunderstorms.”

Di Martino was hesitant to guess at just how much warmer than average the coming months may be.

“As a meteorologist I never like using terms like ‘hottest ever,’ ” he said. “There’s no strong correlation between having an El Niño and a hot year everywhere. There are a lot of competing [natural] factors alongside anthropogenic global warming.”