Subscribe in a reader


Username
Password
Keep me logged in
New? Register here
Forgot your password?


It's the sun
Climate's changed before
There is no consensus
It's cooling
Models are unreliable
Surface temp is unreliable
Ice age predicted in the 70s
We're heading into an ice age
It hasn't warmed since 1998
Antarctica is cooling/gaining ice
View All Arguments...


Latest Posts


What is the link between hurricanes and global warming?

The skeptic argument...

Gore claims global warming is causing more frequent and severe hurricanes. However, hurricane expert Chris Landsea published a study on May 1 documenting that hurricane activity is no higher now than in decades past. Hurricane expert William Gray reported just a few days earlier, on April 27, that the number of major hurricanes making landfall on the U.S. Atlantic coast has declined in the past 40 years. Hurricane scientists reported in the April 18 Geophysical Research Letters that global warming enhances wind shear, which will prevent a significant increase in future hurricane activity.

What the science says...

It is unclear whether global warming is increasing hurricane frequency but there is increasing evidence that warming increases hurricane intensity.

There are two aspects to hurricane activity that are often confused so it helps to consider them separately. Specifically, does global warming cause more frequent hurricanes and does it cause more intense hurricanes?

Hurricane frequency

In July 2007, Greg Holland of the National Center for Atmospheric Research and Peter Webster of Georgia Tech published a paper Heightened Tropical Cyclone Activity in the North Atlantic: Natural Variability or Climate Trend? that notes an increase in the number of observed hurricanes in the North Atlantic over the past century, concluding "increasing cyclone numbers has lead to a distinct trend in the number of major hurricanes and one that is clearly associated with greenhouse warming".

However, this was refuted by Chris Landsea's Counting Atlantic Tropical Cyclones Back to 1900 stating "improved monitoring in recent years is responsible for most, if not all, of the observed trend in increasing frequency of tropical cyclones". In other words, the reason we're recording more hurricanes is due to our improved ability to observe them thanks to aircraft, radar and satellites.

In addition, a 2007 paper by Gabe Vecchi, Increased tropical Atlantic wind shear in model projections of global warming looked at the results of 18 climate models and concluded increased wind shear from rising sea surface temperatures make it more difficult for hurricanes to form and grow.

Now it seems to me there's a dare-I-say hockey stick trend from the mid-80's, nearly two decades after all observing techniques have come into play. Nevertheless, I would tentatively conclude the topic of hurricane frequency is one area requiring further research and better data.

Hurricane Intensity in the Atlantic

Kerry Emanuel wrote the definitive paper on hurricane intensity Increasing destructiveness of tropical cyclones over the past 30 years. Emanuel found a close correlation between hurricane intensity in the Tropical Atlantic and sea surface temperature. He also suggests wind shear has much less effect on hurricane intensity than increased sea temperatures. This is confirmed by the observed data:

Hurricane intensity in global satellite records

Elsner 2008 used global satellite data from 1981 to find any long term trend in maximum wind speed against different strength hurricanes:

Figure 1: Trends in  tropical cyclone maximum wind speeds by quantile, from 0.1 to 0.9 in increments of 0.1. The point-wise 90% confidence band is shown in grey. The solid red line is the overall trend and the dashed red lines delineate the 90% point-wise confidence band about this trend.

Overall, there is a statistically significant upward trend (the horizontal red line). But more significantly, Elsner found weaker hurricanes showed little to no trend while stronger hurricanes showed a greater upward trend. In other words, stronger hurricanes are getting stronger.

While Elsner found no trend in the overall number of hurricanes, the increasing intensity means there are an increasing number of storms with a maximum wind speed exceeding 210 kilometres per hour (category 4 and 5 storms). The inevitable conclusion is that as sea temperatures continue to rise, the number of Category 4 and 5 hurricanes hitting land will inexorably increase. That coupled with rising sea levels is a bleak prospect. More on Elsner's paper...

Printable Version

Acknowledgements

The image North Atlantic Tropical Storms and Observing Techniques is courtesy of Global Warming Art.

Emanuel's graph of PDI versus temperature was courtesy of Climate 411.

Further reading

Comments 1 to 3:

  1. Will Nitschke (www.capitaloffice.com.au) at 16:09 PM on 19 December, 2007
    A well balanced article. Excellent. Thank you!

    "It's important to remember that hurricane activity is just one possible side-effect of global warming. While the empirical evidence linking global warming and hurricane intensity seems robust, it has no bearing on the central question of whether human CO2 emissions are causing global warming."

    True, but if human CO2 emissions causing global warming do not have damaging consequences, such as increased storm activity, the 'central question' is no longer central, is it?

    Some interesting data on hurricanes:

    Fewest Northern Hemisphere Hurricane Days since 1977. 3rd Lowest since 1958 (behind 1977 and 1973). See:
    http://www.coaps.fsu.edu/~maue/tropical/
    [ Response: If the only consequence of global warming was increased hurricane activity, then you'd have a point. However, they are the tip of the iceberg (pardon the pun). See positives and negatives of global warming for a more comprehensive list. ]
  2. Will Nitschke (www.capitaloffice.com.au) at 22:26 PM on 22 December, 2007
    Your list of potential catastrophes makes interesting reading. But there are no citations, so I wonder how many of these items are speculations and how many have any scientific backing to them. Presumably if the global temperature dropped 2C then we could construct an equally long list of potential catastrophes. It seems that the implications of all this is that somehow, miraculously, the current average global temperature must be perfect.
  3. http://www.physorg.com/news116687408.html

    "Titled "Effect of Remote Sea Surface Temperature Change on Tropical
    Cyclone Potential Intensity," their study found that long-term changes
    in potential intensity are more closely related to the regional
    pattern of warming than to local ocean temperature change. Regions
    that warm more than the tropical average are characterized by
    increased potential intensity, and vice versa. "A surprising result is
    that the current potential intensity for Atlantic hurricanes is about
    average, despite the record high temperatures of the Atlantic Ocean
    over the past decade." Soden said. "This is due to the compensating
    warmth in other ocean basins."

    "As we try to understand the future changes in hurricane intensity, we must look beyond changes in Atlantic Ocean temperature. If the Atlantic warms more slowly than the rest of the tropical oceans, we
    would expect a decrease in the upper limit on hurricane intensity,"
    Vecchi added. "This is an interesting piece of the puzzle."
    - A. McIntire

Post a Comment

Foul language, trolling, personal attacks or non-relevant links will be deleted.

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

© Copyright 2009 John Cook