Today marks the official start of North Atlantic hurricane season. So…
One of the key differences between genuine climatology and anti-scientific denialism of anthropogenic climate change is the flexibility of the former and the stubbornness of the latter when it comes to our ever-evolving understanding of how the world works. The connection between hurricanes and climate is a perfect example.
When the “An Inconvenient Truth” crew was filming Al Gore deliver his now-familiar presentation, they couldn’t have anticipated that two major hurricanes would, as if on cue, roar through the Gulf of Mexico and inflict some $80 billion in damages to the U.S. coast. From a marketing point of view, the timing was perfect. When the film was released the next year, a mirror image of Katrina’s cloud pattern Photoshopped into the emissions of a smokestack told the whole story as a publicity poster. Later, Gore added a long series of satellite photos of the recent hurricane activity to his presentation, the one he trained a couple of thousand activists to take to the world.
The scientific basis for linking hurricane activity and global warming was relatively weak in 2005, although at the time, the papers that scientists like Kerry Emanuel were publishing suggested that a warming ocean should increase tropical cyclone intensity, if not frequency. Emanuel’s 2005 Nature paper that received the most attention concluded that “future warming may lead to an upward trend in tropical cyclone destructive potential.”
In the two or three years that followed, however, a lot of second guessing was done, and more than a few scientists voiced their doubts about the strength of the link. The objection was not so much that global warming won’t make storms more frequent or powerful, but that we don’t really understand enough about how hurricanes form and evolve, or just what the historical record is, to able to state with sufficient confidence just what will happen as the Earth warms. Chris Landsea, a climatologist who is sometimes falsely included in the tiny list of scientists who reject AGW, wrote in Eos in 2007 a typical summary of the problem:
Researchers cannot assume that the Atlantic tropical cyclone database presents a complete depiction of frequency of events before the advent of satellite imagery in the mid-1960s…
Climate denial bloggers regularly pummeled scientists with accusations that they had overstated the link, turning hurricanes into something of an albatross rather than an icon of global warming.
But of course, those accusations did nothing to affect the actual science, which continued apace. To someone who only occasionally checks in with the climate journals, it might seem like the pendulum was forever swinging back and forth between alarmism and dismissal. But to those working inside the field, it was a different story. the period of the pendulum continues to shorten, and this year we’ve seen several papers that suggest we might finally be getting a decent idea of what’s really going on.
In Februrary, Nature Geoscience published the latest thinking from a World Meterological Organization Panel, which included Emanuel, Landsea and several other leading researchers. Here’s their conclusion:
… future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2-11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6-34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre.
Just a few weeks ago, Emanuel took another stab at the notion that some climate models were predicting fewer hurricanes, not more. in a paper delivered to the 29th Conference on Hurricanes and Tropical Meteorology in May, he wrote that those models don’t adequately capture the complexities of the interaction between air near the surface of the ocean and stratosphere.
“My results suggest that future warming may lead to an upward trend in tropical cyclone destructive potential, and–taking into account an increasing coastal population — a substantial increase in hurricane-related losses in the twenty- first century.
lead to an upward trend in tropical cyclone destructive potential.”
Does all of this mean Al Gore was right to focus so much on hurricanes? At the time, it can be argued he was getting ahead of the science and maybe that’s true. But the point is, science is willing to admit that conventional wisdom is not perfect. Given the dearth of hard data five years ago, the best anyone could do was made a rough guess, which is what both Gore and the climatology community were doing. Given the stake if that guess turns out to be right, is that really such a bad thing? At worst, you can accuse Gore and perhaps some scientists of not communicating the involved degree of uncertainty well enough.
Compare that with the refusal of many deniers to accept their errors. For example, no matter how many times you point out that water vapor is not a climate forcing, but a feedback, the argument never seems to go away. Same with the notion that the world stopped warming in 1998. The data say otherwise, but it’s hard to convince those who haven’t bothered to study the facts first. Are there really 30,000 climatologists who object to the IPCC consensus? No. But that meme is proving extremely hard to kill.
So, as we begin the 2010 hurricane season, which could be relatively active, it would wise not to jump on every storm as proof of anthropogenic global warming. But it would be an even bigger mistake not to think about the consequences of more powerful, and perhaps more frequent, hurricanes in the decades ahead. Are we really comfortable with even a small risk of leaving such a legacy for our offspring?