Hurricanes and Global Warming – Is There a Connection?

Finally, then, we come back to Katrina. This storm was a weak (category 1) hurricane when crossing Florida, and only gained force later over the warm waters of the Gulf of Mexico. So the question to ask here is: why is the Gulf of Mexico so hot at present – how much of this could be attributed to global warming, and how much to natural variability? More detailed analysis of the SST changes in the relevant regions, and comparisons with model predictions, will probably shed more light on this question in the future. At present, however, the available scientific evidence suggests that it would be premature to assert that the recent anomalous behavior can be attributed entirely to a natural cycle.

But ultimately the answer to what caused Katrina is of little practical value. Katrina is in the past. Far more important is learning something for the future, as this could help reduce the risk of further tragedies. Better protection against hurricanes will be an obvious discussion point over the coming months, to which as climatologists we are not particularly qualified to contribute. But climate science can help us understand how human actions influence climate. The current evidence strongly suggests that:

(a) hurricanes tend to become more destructive as ocean temperatures rise, and

(b) an unchecked rise in greenhouse gas concentrations will very likely increase ocean temperatures further, ultimately overwhelming any natural oscillations.

Scenarios for future global warming show tropical SST rising by a few degrees, not just tenths of a degree (see e.g. results from the Hadley Centre model and the implications for hurricanes shown in Fig. 1 above). That is the important message from science. What we need to discuss is not what caused Katrina, but the likelyhood that global warming will make hurricanes even worse in future.

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1. By ‘destructive’ we refer only to the intrinsic ability of the storm to do damage to its environment due to its strength. The potential increases that we discuss apply only to this intrinsic meteorological measure. We are not taking into account the potential for increased destruction (and cost) due to increasing population or human infrastructure.

References:

Delworth, T.L., Mann, M.E., Observed and Simulated Multidecadal Variability in the Northern Hemisphere, Climate Dynamics, 16, 661-676, 2000.

Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: 10.1038/nature03906

Goldenberg, S.B., C.W. Landsea, A.M. Mestas-Nuñez, and W.M. Gray. The recent increase in Atlantic hurricane activity. Causes and implications. Science, 293:474-479 (2001).

Kerr, R.A., 2000, A North Atlantic climate pacemaker for the centuries: Science, v. 288, p. 1984-1986.

Knutson, T. K., and R. E. Tuleya, 2004: Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. Journal of Climate, 17(18), 3477-3495.

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317 comments on this post.
  1. JimG:

    I am not sure if I believe the “Hurricane results in a Net Gain for the Economy” line of reasoning, since the money spent on fixing hurricane damage, could be spent instead, say, on installing solar panels, if there were no hurricane damage, and installing solar panels would help to mitigate global warming, while fixing what breaks does not mitigate global warming.

    200 billion in solar panels, and their installation, would make a big difference, and would create just as many construction jobs and manufacturing jobs, as hurricane damage re-construction. (It’s what economists call the “opportunity cost” which this “net gain for the economy” reasoning misses.)

  2. Gerald Machnee:

    Re # 298 – I was not questioning the reporting of a theory – you are making the issue complicated – I was saying that measuring the amount of GW or AGW is difficult or almost impossible with instruments — that’s it!
    Re # 300 – Again I am not saying that CO2 or other parameters are not changing or we are not measuring them. However, CO2 is small compared with water vapor in the atmosphere, so therefore the total change in greenhouse gases is not as great as the change in CO2. So if CO2 changes 35 percent, the change in greenhouse gas total is less than a percent. Anyway, my point is the same as above – hard to measure the exact amount of influence – good career opportunity!!
    RE # 299 – “It indicates a connection, since, over the last few centuries (since people have been inhabiting the coast of Brazil in rather large numbers), no TCs had ever been recorded.

    This is likely due to SSTs being sufficiently warm for the formation of these storms when previously, the SSTs inhibited TC/TS/TD formation. This would lead most scientists to conclude that the oceanic warming needed for storm development is likely due to human-induced climate change.”

    I have not looked at this area in detail which is why I opened with a question in my response. In other words – Has the SST increasd? When I noted lack of reporting sites, I was quoting from scientific reports. You indicated that people have been living there a long time – but the scientists noted a lack of reports. You have to realize that the records there may not be as good as in North America. To have a report on the coast – the storm has to make landfall. One report noted that there may have been less ship activity therre compared with the north Atlantic so less storms may have been encountered. Even if SST is high enough, you still need the right meteorological conditions to form the storm or hurricane. I believe that there is less cyclone activity in the southern hemisphere than the north.
    “Maybe atmospheric temperatures were cooler than normal. However, SSTs were likely not! ”
    This report came from scientists who noted the cooler conditions. Have you checked the SST’s? Scientists did indicate that they would have to rely more on satellite photos for observing activity.

  3. Gerald Machnee:

    Further to Catarina, the following quote is from a UCAR site:

    “Already, southern Brazil’s summer had been a strange one. “January and February 2004 were the coldest in 25 years,” notes modeler Pedro Leite da Silva Dias (University of Sao Paolo). Although Catarina was later tagged by some as a possible sign of climate change, the waters over which it formed were actually slightly cooler than average. However, “the air was much colder than normal,” says Dias. This produced the same type of intense upward heat flux that fuels hurricanes, normally seen in warmer waters.”

    Other sites indicate that one of the main reasons for a lack of hurricanes there is the wind shear is too great.
    You can find studies on this hurricane by searching “Hurricane Catarina”

  4. weather.com weblog:

    New Investigation of the Global Warming – Hurricane Connection
    For better or worse, the 2005 hurricane season generated a lot of interest in the link between global warming and hurricanes. A new study published this week in Science Express attempts to further nail down the link between warmer ocean…

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