Ocean changes mean weather events like Sandy to become more common

Hurricane Sandy blasted the East Coast last month with a fearsome and deadly deluge. A Scripps Institution of Oceanography, UC San Diego-led team published research a few days later that continues the steady trickle of evidence that flooding like the kind Sandy brought is about to become more common.

Scripps climate researcher David Pierce and colleagues had already laid out the case in a series of papers dating back to 2001 that the observed temperature rise of the upper oceans over the last 50 years could only be explained by human-induced global warming. Pierce and others have now reported the same holds true for trends in ocean salinity. Across the world’s oceans, salty areas have generally gotten saltier; regions of relatively fresh water have gotten fresher. These trends could only be explained in the context of the atmospheric warming that has taken place because of the buildup of greenhouse gases caused mostly by human fossil fuel use.

Relative saltiness matters because it helps scientists understand what to expect of ocean circulation. Changes in saltiness mean changes in water density, which in turn change how water moves. More to the point of Sandy, these trends show that there are already changes in the world's hydrological cycle — the continual process of evaporation and precipitation that moves water from the oceans, into the sky, into soil through rain and snow, back to the oceans as precipitation and runoff. There is a human footprint, and it can be found on the accelerator of that cycle. It’s getting faster.

Increasing salinity in the upper ocean means water is evaporating from its surface faster. More rapid evaporation loads the atmosphere with more water vapor, but the natural tendency of that water is to come back down to Earth at its earliest opportunity. Precipitation intensifies, whether at sea or on land. It is more likely to fall in torrents. The inverse is true in places given to drought. Weather happens faster, harder. Think of the monsoon that hit Pakistan just two years ago. One-fifth of the entire country was underwater at one point.

The frenzied pace of precipitation adds to the other variables fortified by climate change that make storms stronger. For instance, the same forces that are making the oceans warmer are causing sea level to rise. Sandy was frightening enough by itself, but some of the informal postmortems circulating among climate scientists are even more so: At the Battery, at Manhattan’s southern tip, a 9-foot storm surge peaked at the same time as a 5-foot high tide.

That 14 feet of extra sea surface height broke the record that had existed since 1920 by a full 4 feet. If the most conservative estimates hold true, a similar storm hitting New York at high tide 75 years from now will be another 3 feet higher. In 2300, the low end of estimates (albeit with a larger margin of error) calls for sea level to be 8 feet higher.

Do you even want to know what the high-end estimate is? OK, I’ll just tell you. It’s 16 feet.

It will be Sandy every day.

In the context of all this, the widespread discussion in the United States that climate change needs to be taken seriously is refreshing. New York City Mayor Michael Bloomberg goes further than most scientists will in directly linking Sandy to climate change.

Climate researchers look at what’s happening in a more measured way. Book author and Scripps Professor Emeritus Richard Somerville is reminded of the analogy between climate change and the performance of a talented baseball player who begins taking steroids. He might have hit home runs before juicing himself, just not as many. Human-caused climate change is the steroid in this analogy. You’ll never know which home runs were caused by its use. You’ll just come to expect more and more anomalously crazy seasons until someone takes action.

Monroe is editor of UC San Diego's Scripps Institution of Oceanography explorations now online magazine.

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