We already know that anthropogenic global warming (AGW) is likely to increase tropical storm intensity in the future (Table 1, pg. 15), due to increased global warming. The wrong question at the intersection of science and policy to be focusing on is this one about the present, not the future:
“Thinking about the increase in the number and strength of hurricanes in recent years, do you think global warming has been a major cause, a minor cause, or not a cause of the increase in hurricanes?”
Of course that's the one that everyone focuses on, and as a conformist, I will too. But first, some other questions and their answers.
1. Does controlling land use to prepare for hurricanes/typhoons have more effect on reducing their impacts than controlling greenhouse gas emissions? Yes - if proof was ever needed for this, there's plenty of it at Prometheus.
2. Because land use changes will do more to protect from hurricanes, should we be forbidden to consider the benefit that reducing GHG emissions will have on reducing tropical storm damage? No - reducing storm damage is a real benefit of fighting emissions that should be considered while deciding policy. Focusing attention on the problem of increased future storm damage could actually benefit efforts to improve land use.
3. Is there any reason to ignore AGW-caused storm damage after 2050? No, unless you think there will be no AGW after 2050. In fact, AGW will have worse storm effects after 2050, and the artificial cut-off results in bad policy that ignores available science.
I expect Roger Pielke Jr. is right that some have exaggerated the extent we can connect the dots right now between current AGW and current hurricanes, but it really doesn't matter as a policy question. The reason to change GHG policies now is because of their future effect of emissions, and we already know our policies are likely to have a future effect, and should therefore be changed.
But since everyone wants to focus on the question of current effects, let's do it. If AGW is currently worsening hurricanes, then that's one more reason to change policies. Just as there is a consequence for acting incorrectly, there's also a consequence for inaction. While current science hasn't finished connecting the dots and telling us that AGW definitely is worsening hurricanes, it doesn't deny a connection either. The question of current effect is best phrased as a question of what probability science now assigns to AGW having a current effect on storms.
Readers of this blog will know I'm a one-trick pony when it comes global warming and probability - let's set up a bet! My bet is that the International Panel on Climate Change's Sixth Assessment Report, will say that AGW likely intensified tropical storm damage from at least 2005 onward. I believe science says it's more likely than not that we already have a problem, and I'm probably not going far out on a limb to say that.
It's not a very strong signal that science is sending to policy-makers, and it's not a very important one because we already know that we will have a problem with future hurricanes from AGW, but if people disagree on connecting current storm activity to AGW, they should consider betting me.
FWIW, I've submitted this as a bet offer to Longbets.org in case someone wants to bet for charity rather than get the money back. It might take some time for the bet offer to register, but it should come up here.
UPDATE: light edit for politeness.
UPDATE 2 (April 2012): edited to move to it back to AR6 and to start the period in 2005 - looks like they're not ready to make the conclusion just yet.
key: global warming, bet