Did global warming cause hurricane Irene?

Scientists can't say that global warming caused hurricane Irene or Katia or tropical storm Lee. But they can say that global warming produces the conditions that lead to hurricanes. Americans should be reducing greenhouse gas emissions and preparing for severe weather to come.

Opinion

Like many people, I spent the last weekend in August mesmerized by the steady progress of hurricane Irene as she followed the script so carefully laid out by the National Weather Service’s Hurricane Tracking Center. Not too long ago, hurricane prediction was more like trying to guess the direction that an improvisational theatrical performance was going to take. However, as the science has improved, some of the apparent spontaneity of hurricanes has disappeared.

Nevertheless, there remain questions that scientists cannot and never will be able to answer with certainty. One of these unanswerable questions, literally a billion-dollar question, is the following: Is global climate change responsible for a given hurricane or any other weather disaster?

Scientific answers to this question can be either simple or complex. The simple answer is that we cannot know with absolute certainty that global climate change caused any particular weather event. However, the science is improving to the point that we can begin to start assigning probabilities to such events as the Earth’s climate warms in response to humanity’s continuing emissions of greenhouse gases.

For example, in the case of Irene, we cannot say that global climate change bears any responsibility for the havoc wrought by this particular hurricane. On the other hand, we do have the knowledge and scientific tools to predict how greenhouse warming will increase the likelihood of future hurricanes exhibiting Irene’s magnitude and track along the eastern seaboard of the United States. We know for instance that the warm oceanic waters of the tropics serve as the heat engine for hurricane development. Therefore, as these oceanic waters are warmed further, a greater number of intense hurricanes like Irene will make landfall in North Carolina.

Furthermore, we know that hurricanes begin to weaken after they make landfall and must return to the warm oceanic waters offshore to rebuild their intensity. As the autumn water temperatures of the Mid-Atlantic Bight continue to rise each decade, hurricanes like Irene will be able to strengthen and more frequently carry their destructive forces further north to New Jersey, New York, and New England.

So, what does this all mean to the average American on the street? Well, since hurricane Irene just pushed 2011 past 2008 in the record books for the most billion-dollar weather disasters in a year, it certainly seems logical that people should expect higher taxes.

Because no matter what a given state’s political leaders may think about global climate change or taxes, they all expect help from the federal government when extreme weather disasters strike. Whether it's droughts and wildfires in Texas and Oklahoma, tornados in Missouri and Arkansas, floods in Tennessee and Mississippi, or hurricanes in North Carolina and New Jersey, the lineup of states seeking federal assistance keeps getting longer and longer this year.

Can we blame global climate change for all of these extreme weather disasters in 2011? Again, the simple answer is no, we cannot attribute global climate change as the cause for any one of these disasters. However, the more important take-home message is that scientists predict all of these types of extreme weather disasters will become more and more common as the planet warms.

Therefore, it would seem to be more prudent and cost effective to stop ignoring the effects of greenhouse warming on our weather. Wisdom would also have us begin reducing our greenhouse gas emissions and preparing our society for the impending weather disasters already in the pipeline.

Charles H. Greene is a professor of Earth and Atmospheric Sciences at Cornell University.