Q & A on Role Global Warming Plays With Extreme Weather Such as Hurricane Sandy
Oct. 26, 2012 -- As residents in mid-Atlantic states and New England brace for Hurricane Sandy, many may wonder what role global warming is playing with this "Frankenstorm." Here to explain the linkage is a Q & A with climate scientist Dr. Jennifer Francis, research professor at the Institute of Marine and Coastal Sciences, Rutgers University.
Is global warming extending the hurricane season and also the range of these storms?
Warm ocean temperature is one of the main ingredients necessary for tropical storms to form and survive, so the fact that the oceans in general are warming and that sea-surface temperatures are now at an all-time record high off northeast N. America suggests that any late-forming storms that move up this way, like Sandy, should be able to survive longer and track farther northward.
The warming of the Arctic brought record-setting ice loss this year. How is that ice loss and the warmer Arctic affecting our weather?
Our research suggests that the fact that the Arctic is warming twice as fast as the rest of the globe is having two effects on the jet stream that play into weather patterns all around the northern hemisphere. One is to reduce the temperature difference between the Arctic and areas farther south, which tends to weaken the west-to-east winds in the jet stream. A weaker flow tends to make the jet stream take larger north-south excursions, just like a river tends to meander more as it flows across a shallow-sloped coastal plain. The other effect is to stretch the northward peaks of waves in the jets stream farther north, which enhances the size of the waves and consequently the chances of blocking patterns, like we're seeing now in the conditions steering Sandy. Both of these effects of Arctic warming tend to make the jet stream wavier, and as those waves get larger, they tend to move more slowly, which means the weather associated with them also moves more slowly...leading to increased chances of the types of extreme weather associated with "stuck" weather patterns.
If global average temperatures are getting warmer, why are we seeing snow storms in October?
For the reasons explained above, the larger waves in the jet stream bring warm air farther north as well as cold air farther south, where it can interact with moisture to create snowstorms earlier in the season (e.g., Halloween storm of 2011) and farther south (e.g., snow in Morocco last winter).
Did the warmer Arctic create the "blocking high" that prevented Sandy from moving out into the Atlantic?
We can't say for sure that the warmer Arctic created the block, as blocking patterns occur naturally, but it may have played a role in making it stronger or extending the ridge of high pressure farther northward or keeping it in place longer than it would have when the Arctic had more ice only a few decades ago.
Has the weakened jet stream increased the chances that winter storms and tropical storms would collide?
To my knowledge there is no research that has suggested this to be true, but considering the possible lengthening of the tropical cyclone season owing to warmer oceans, the ability of tropical storms to travel farther northward before they encounter cold water, and the larger southward dips in the jet stream owing to a warmer Arctic, then it's conceivable that the situation we're seeing unfold this week may become more likely as global warming continues unabated.
CONTACTS: Dr. Francis can be reached at francis@imcs.rutgers.edu.
For other questions about Citizens Climate Lobby, contact Steve.Valk@citizensclimatelobby.org.
