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The story of climate change is largely a story about what's happening to the ocean. Most of the damage during Superstorm Sandy, after all, had nothing to do with the rain or wind. It was the rising ocean that swamped Staten Island, flooded the Rockaways, and knocked out power and subway service in lower Manhattan for days. People noticed the hurricane sweeping up the coast. But it was the already high ocean that did the damage.

Which is why it's worth paying attention to the National Oceanic and Atmospheric Administration's newly-completed assessment of how climate changed during 2012. Ocean surface and land temperatures are increasing, water temperatures below the surface remain warm — and sea levels have never been higher.

A report last month suggested that sea level rise could overwhelm large areas in scores of cities this century alone, as Quartz reported. The NOAA's report suggests that the trend showed no sign of slowing last year.

Sea level has been rising over the past century, and the pace has increased in recent decades. Part of the increase is due to more water being added--meltwater from glaciers and ice sheets--and part of the increase is due to rising water temperatures: water expands in volume when it gets warmer.

Since satellite-based global measurements began in 1993, global mean sea level has risen between 2.8 and 3.6 millimeters per year (0.11-0.14 inches/year). In the most recent period (2005–12), meltwater entering the ocean has dominated sea level rise, accounting for more than twice the contribution from warming-caused expansion.

The agency has a map of where that rise is more prominent, affecting the Northeastern states and Gulf Coast of the United States in particular. The green arrows on the map below are those that are seeing sea level rise at the low end of the estimate above. The agency's larger map indicates that sea levels near New Orleans increased at a rate of 9.24 millimeters a year between 1947 and 2006 — three feet over the course of a century.

At the same time, the surface temperature of the ocean off the Northeastern coast was about seven degrees above average last year. Across the globe, surface temperatures in 2012 were among the eleven warmest years on record. Every year this century has seen surface temperatures above the 1981 to 2010 average. Among other things, warmer sea water temperatures can affect power production when ocean water is used to cool facilities. Last August, a nuclear plant was forced to shut down a reactor due to warm water temperatures.

Much of the heat created in the atmosphere has been buried far beneath the surface of the ocean. The NOAA report notes that this retained heat affects "the ocean’s ability to store and release heat over long periods of time," destabilizing the climate.

Land temperatures were also higher than normal, placing 2012 among the ten warmest years on record. The United States had its hottest year in recorded history, wracked by a drought that continues to cripple the Southwest. In 2011, a researcher from Columbia University argued that the Southwest would move into a state of permanent drought as temperatures rose over the decades.

Then there's the Arctic, which is well into a dangerous warming cycle, as we reported last month. The NOAA states that in 2012 the Arctic warmed at twice the rate of lower altitudes, including a massive melt in Greenland and increased permafrost thaw.

But of all of these bad signs, it's that ocean level that should inspire the most immediate concern, as it did when it flowed over the barriers protecting New York City last autumn. 40 percent of Americans and 44 percent of everyone on Earth lives within 150 kilometers of the sea. However slowly climate change creeps up on us, one of the first things we should notice is how high the ocean is getting. If we don't, the NOAA will likely remind us next year.

Photo: A man stands in his flooded Louisiana home last year. (AP)

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