Some say ice

Notwithstanding the thaw we’ve experienced this week, we have had an unusually blustery winter so far—indeed the snow started a month or so before the official start of winter. Our latest NYSEG bill shows average temperatures in this year’s December billing period a full 10 degrees below last year’s, and the thaw is forecast to disappear in fairly short order.

So what happened to all that global warming? Where are the Carolina winters we’re supposed to be headed for?

The problem is that “global warming,” in the sense of an increase in overall global temperatures, is a much more complex phenomenon than an increase in temperatures at all locations and at all times. This is probably why many have dropped the term “global warming” in favor of “climate change.”

To begin with, the temperature patterns in any one place aren’t the same as for the planet as a whole. Climate change skeptics recently felt that they scored a great coup when they pointed out an error in NASA data that had shown 1998 as the warmest year in recorded U.S. history when, in fact, it turns out 1934 was the warmest and half of the 10 warmest years on record here occurred before World War II.

But that error did not affect the global picture. The National Oceanic and Atmospheric Administration of the Department of Commerce still reports that, globally, 1998 was the warmest year on record, and seven of the eight warmest years for the planet as a whole occurred since 2001. It is unlikely that any particular locality will follow the global average exactly, but it’s the global average that tells us the direction of the trend.

Climate change is expected to lead to greater extremes of temperature and precipitation and more violent weather events. The extremes of temperature will average out warmer, but that doesn’t mean it will always be warmer in any one place or any one season. The same goes for precipitation. Hotter air can hold more water vapor, leading to an increase in precipitation and flooding overall. But extremes of high precipitation in some localities are expected to be coupled with extremes of drought in others. The two extremes will average out to more precipitation around the globe—but not in all places.

The complexity of the changes that can be brought about by higher global temperatures is probably best illustrated by the so-called “abrupt climate change” scenario. This scenario is something nobody considers to be a high likelihood, but is a real enough scientific contingency that the United States Pentagon ordered a study on it that was performed in 2003. ( see mindfully.org/Air/2003/Pentagon-Climate-Change1oct03.htm ).

In the abrupt climate change scenario, the rise in temperature, which is expected to be more extreme in northern latitudes than at the equator, results in a release of massive amounts of fresh water into the northern oceans due to a combination of ice melt and fresh-water river runoff. This, in turn, shuts down the so-called thermohaline current, driven by cold, salty water, which is denser than fresh water, sinking in northern latitudes and pulling warmer water up from the equator. By shutting down currents like the Gulf Stream, which gives Western Europe and the Northeastern United States a temperate climate, stopping the thermohaline current would reduce temperatures in those two areas between five and 10 degrees Fahrenheit (while raising temperatures by similar amounts elsewhere). Evidence from previous stoppages of the thermohaline current suggests that this could happen in less than 10 years.

The abrupt climate change scenario is considered highly unlikely (though one might note that scientists in 2007 found that their forecasting models have drastically underestimated the speed with which arctic ice is melting), but understanding how the mechanism could work warns us against oversimplifying our expectations. With regard to climate change, as with respect to so many other things, we need to be conscious of what is happening globally, of the extent to which human behavior affects planet-wide systems, and how they in turn can affect our locality. One winter, or one summer, whether warm or cold, is not the stuff of which climate change is made. On this issue, we must endeavor to think and to act within a perspective that is both long term and worldwide.

Dr. Punnybone

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