State of the Planet

News from the Columbia Climate School

On the Surface of Climate Change

Blog Action Day 2009’s theme this year is Climate Change. Thousands of people on blogs all over the world are writing today on this single issue, and the Columbia Water Center is joining them.

On Climate

In a recent study at Columbia University, correlations were drawn between sea surface temperature on the coast of Africa and streamflow at the inlet of a reservoir at the head of the Delaware River.

While it seems strange, at first, that New England can be affected by water temperature shifts of a very few degrees Celsius on the other side of the world, it makes more sense when we look at the pathways of our seasonal storms.

stormStorms that come at us in New England from the Midwest originate in build-ups of energy and moisture collected off of the Gulf Mexico, then travel up through North America along the Mississippi and Ohio River valleys. Our hurricanes, before raging up the east coast of North America, travel across the equator from origins on the west coast of North Africa.

The pathway of the correlation between sea surface temperatures and streamflow, then, becomes clear. With warmer water temperatures, there is more energy buildup on the surface, which in turn leads to more (or at least more intense) storms traveling along the storm trajectories, more precipitation arriving in New England, and more streamflow finding its way to the Delaware River.

On Climate Change

Scientists have developed complex global climate models to assess current and future climate based on a number of greenhouse gas emissions scenarios. The impacts of global warming will vary depending on which trajectory emissions actually follow, though there is a broad agreement across all scenarios that a change of approximately 2 degrees Celsius is nearly unavoidable. Most disturbingly, the observed global rates of temperature and greenhouse gas increases to-date have exceeded all the near-term model projections. These results are all the more frightening when one considers the resistance to action exhibited by the world’s largest greenhouse gas emitters.

If sea surface temperatures rise, when greenhouse gases prevent the release of water heat back out into the atmosphere, the threat of global ramifications—in terms of unprecedented storms, floods, or other extreme weather events—are very real.

Sea surface temperatures are rising, certainly. Over the past 150 years, average sea surface temperatures have risen about one degree Celsius.


Interestingly, however, they are not doing so at the projected rate. What this means is that while the underlying trend may be one of warming, parts of the globe may experience extended periods (5-10 years) of no warming, or even cooling.

All of this said, sea surface temperature is hardly the only factor of climatic behavior. It would be an easy system if, when sea surface temperatures rose in one place, frequency and/or intensity of storms rose in another—potentially, in the case of drastic climate change over time, causing potential flooding or storm damage. This is, to be fair, often the case (many studies have been done on this subject, linking sea surface temperature with either intensity or frequency of storms, or both).

It is possible, however, that the opposite actually happens. Even if sea surface temperature were to increase, and were to lead to significantly more hurricanes, other indirectly related factors, like changes in circulation, could prevent the storms from ever getting north of Virginia. The reservoir along the Delaware River, then, might paradoxically find itself in a drought.

There are a huge number of factors involved in analyzing current climate realities—not to mention predicting any future realities, or protecting against them.  The idea behind modeling is to create something simpler than reality. It is the challenge of scientists and researches, when constructing forecasting models for the future of our global climate, to work on the best compromise between simplicity and breadth, between feasibility and reliability.

Climate change is, inconveniently, a complicated truth.

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