Sandy triggers climate blame game



Hurricanes may become less frequent but more powerful in the future, studies suggest

The floodwaters whipped up by Hurricane Sandy have not yet receded but the temperature is rising on one of the toughest questions in modern science: whether we're getting more extreme weather because of global warming.

Radical film-maker Michael Moore put it with characteristic bluntness. In a Tweet, he wrote: "Stop w/ the disaster porn and tell the America people the bitter truth: We have f***** up the environment & we are now paying the price."

The governor of New York state, Andrew Cuomo, expressed it more politely: "Anyone who thinks there isn't a change in weather patterns is denying reality."

And to widespread surprise, New York Mayor Michael Bloomberg also made a link between Hurricane Sandy and global warming, though more guardedly.
"Our climate is changing," he said in a statement last night, remarkable in itself in the context of a presidential election year in which the word "climate" did not get a mention in any of the contenders' debates.

Mr Bloomberg did not seek to pin any direct blame on climate change - in fact what he said actually reflects the current of the science rather accurately.

He said the "increase in extreme weather we have experienced in New York City and around the world may be the result of [climate change]."
But "the risk that it might be - given Sandy's devastation - should compel all elected leaders to take immediate action."

The question is one of risk, not of certainty - the risk that the continuing rise in greenhouse gases from human activities may exacerbate extreme weather. To go further, as many environmental campaigners would like to, is to suggest that the violence of Hurricane Sandy is the result of global warming. Scientists are in the process of proving this theory and so far, it looks to be conclusive but not all results are in yet.

At face value it looks obvious: the basic ingredient for a tropical storm is a sea surface temperature above 26C (79F) and, with the oceans known to be warming, that essential condition may occur more often. Wind shear can sometimes kill a storm before it becomes a hurricane but there is no doubt the oceans are warming and this creates perfect conditions for the birth of violent storms.

To say that more warming means more storms is to oversimplify a highly complex situation - and attract a barrage of criticism for unjustified green "alarmism". But the bottom line is that storms are becoming more and more violent and frequent and the only change globally, is climate change.

 The most accurate record of hurricanes - essential for any comparison - only stretches back to the start of the satellite era in the late 1970s.  Before then, there is no way of knowing whether storms which developed at sea then stayed out at sea and grew or died unseen and unrecorded. So the exact frequency and power of ALL tropical storms is only known for the last 30 years or so - too short a period, say  scientists, to form a  conclusive judgment.

What matters they say are the strength, frequency and duration of storms, which they measure with an Accumulated Cyclone Energy Index. A trend is developing in the direction of more frequent and violent storms but they feel there is not sufficient data yet.

 

Recent studies have run computer models of particular weather events - with and without the factor of man-made greenhouse gases - and concluded that they were likely created as a result of the greenhouse effect.
Sandy's growth and journey up the Atlantic; the storm's sudden turn West to the coast after encountering an Arctic high-pressure zone, the collision with a cold weather system - all this is extremely challenging to unpick, and its doubtful whether the science, as it stands, could tackle it rapidly.

If Hurricane Sandy ends up costing US $20bn, it would rank only 17th out of 242 storms to hit the US since 1990.

Arguments to support theory of global warming:

• rising sea-levels gradually increases the risk of coastal flooding - true but over a timescale of decades;
• the record melt of sea-ice in the Arctic during this summer possibly changed the path of the jetstream and therefore the weather patterns - but the science on this is in its infancy;
• the warming of the atmosphere allows it to hold more moisture and therefore deliver more rain - though in the case of Hurricane Sandy, the impact was through wind and the storm surge rather than precipitation.

As the battered communities of the US East Coast try to rebuild their lives, the scholarly arguments about the cause of their misery is not likely to be uppermost in their minds.

But it's brought into much sharper focus one of the hardest questions about climate change: what can the science reliably tell us about what global warming really means for each of us, not just in the future, but here and now?