A Game of Inches or a Game of Feet?

Perhaps no other consequence of global climate change kindles the public’s fears like the prospect of catastrophic sea-level rise.  For years now, climate scientists have recognized the potential for increasing global surface temperatures to produce certain kinds of feedback loops that would accelerate the collapse of massive ice shelves in Greenland and Antarctica, leading to a rise in sea level in the range of 6 to 20 feet by the end of the century.  Such a development would wipe entire island nations off the map and inundate major cities like New York City, dislocating hundreds of millions of people around the world.

In short, whether or not massive ice shelf collapses occur could mean the difference between a rise in sea level of only a few inches versus a rise in sea level of many feet.  The problem is that, until recently, scientists have had no way of accurately predicting the rate at which ice shelves break.  A team of U.S. scientists, however, has developed a methodology for predicting the rate at which ice shelves break.  This methodology will greatly improve the models that are used to predict the future sea-level rise that results from global climate change.

The scientists, led by Richard Alley, Ph.D, of Penn State, developed a list of factors that might contribute to the breaking of ice shelves, such as thickness and straining rate.  They then analyzed the effect these factors have on the rates at which ice shelves break up, by applying them to 20 different ice shelves.  Based on these analyses, the team was able to develop a preliminary methodology for predicting the rates at which any given ice shelf might break up.

This methodology will go a long way toward improving current models for predicting future sea-level rise.  Current models give little attention to the effects of ice shelf collapse on sea-level rise, since the process of ice shelf collapse has been so poorly understood.  As a result, these current models for projecting future sea-level rise are woefully incomplete.  For example, the projections in the most recent report by the United Nations Intergovernmental Panel on Climate Change (IPCC) forecast a rise in sea level of between 7 and 23 inches.  The authors of the IPCC report acknowledge that this forecast essentially ignores the effects of ice shelf break-up, and thus does “not provide a best estimate or an upper bound for sea level rise.”

Undoubtedly, Professor Alley’s model will require refinement in the future.  For now, though, it provides an important first step toward resolving the largest source of uncertainty in predicting future sea-level rise – a source that could produce cataclysmic results.  Resolving this uncertainty will help the world’s policymakers design the most appropriate measures for mitigating greenhouse gas emissions and for adapting to the inevitable consequences of climate change.  Moreover, it may serve as the necessary wake-up call for individuals and nations around the world to make a determined commitment to alter their behavior so as to reduce their carbon footprints.

Recent events in the news remind us that the benefits of improved modeling of future sea-level rise cannot come soon enough.  This week, flooding in Venice, Italy, has reached its highest levels in decades, leaving famous historical and cultural sites in the city, such as Piazza San Marco, covered by a meter or more of standing water.  The flooding is a stark reminder of the effect that climate change—and especially sea-level rise—might have on human health, the natural environment, and irreplaceable human culture if its causes and consequences are not addressed immediately.