As the governor’s commission on climate change starts digging into the impact of Global Warming on Virginia — a particular concern is the expected three-foot rise of sea levels by the end of the century — it would do well to acknowledge the evolving state of climate science. Nearly every day brings some new discovery that refines our knowledge of the mechanics of climate change. The latest, as reported by National Public Radio, highlights “the mystery of Global Warming’s missing heat.”
While surface temperatures on the earth have been warming over the past four or five years, temperatures in the oceans have showed no warming — indeed, according to reports of some 3,000 robotic sensors scattered around the earth’s oceans, known as the Argo system, the waters might actually have cooled a bit. That’s relevant to Virginians for a couple of reasons: (a) the oceans hold significantly more of the earth’s surface heat than the atmosphere does, and (b) the warming of the ocean, which slightly expands its mass, is expected to be a driving force of rising sea levels.
For Virginians, rising sea levels are the cutting edge of climate change. Other than New Orleans, Hampton Roads is the lowest-lying large metropolitan area in the country, and it is exceptionally vulnerable to rising sea levels. Also, the Chesapeake Bay ecosystem is vulnerable to salification as ocean water displaces fresh water in the estuary.
The new Argo system measurements appear to be inconsistent with the predictions of climate change models that temperatures and are destined to rise. Scientists are baffled. Perhaps it’s just a measurement error: The ocean’s heat might be circulating to deeper levels not tracked by the sensors. Alternatively, the earth’s natural thermostats may be allowing more heat to be released into space than expected. Or, concedes Kevin Trenberth at the National Center for Atmospheric Research, there may be a dynamic at work that science has not yet identified.
Here’s another curve ball. In theory, because ocean water temperature should account for about half of rising/falling sea levels, sea levels should not have been rising over the past few years. But they have continued to rise — about 1/2 inch over four years. Scientists guess that the melting of Greenland and Antarctic icecaps may account for the rise. There are so many variables in the climate, however, that nobody knows for sure.
One more thing for Virginia’s climate change commission to think about: If sea levels are rising 1/2 inch over four years, that implies a rate of one inch per eight years. If the rate stays constant for the rest of the century, that implies that sea levels will be 11.5 inches higher — less than one foot — by the year 2100. As I recall, the commission is operating on an assumption that sea levels will rise three feet over that period.
The fact is, nobody knows what sea levels will do, and anyone who speaks with certainty is blowing hot air. What we can say with some confidence is that there is a significant risk, based on our current knowledge, that sea levels will rise. We need to take those risks into account as we plan for Virginia’s future, and we need to continually update and modify our assessment of those risks to reflect the best scientific knowledge as we go forward.
(Image credit: From Vanity Fair, a photo of what Manhattan might look like if sea levels continue to rise, “Notes of Intelligence” blog.)
