Is Global Warming the (partial) cause of Katrina?

[Reloy3]

I guess this thread is an attempt to focus a question being posed in different threads, most of which seem to be about blaming than about facts. So, what is the evidence that Global Warming is a contributing factor to the intensity of Katrina and the frequency of recent hurricanes. Last month’s National Geographic indicates that Global Warming may affect hurricane strength, but probably not until the later half of this century. Instead it blames AMO:

That debate will continue, but many scientists agree that the present hurricane surge is likely part of a 60-to-70-year cycle that changes the strength of ocean currents distributing heat around the globe. Researchers have used tree rings and ice cores to track this variability back hundreds of years. We’re now in a fast-flowing mode of this up-and-down cycle, named the Atlantic Multidecadal Oscillation (AMO), during which Atlantic sea-surface temperatures and wind conditions favor hurricane generation. Ten years from now, or perhaps thirty (the timetable is difficult to predict), the cycle should reverse, tending to suppress major hurricanes

See the rest at: http://www7.nationalgeographic.com/ngm/0508/feature4/index.html

On the other hand, many seem convinced that Katrina is at least partially caused or intensified by global warming. Where is the evidence? I’m not disbelieving, I just want to know what the science is and what is political hype/point scoring.

BTW, this thread is not meant to be another political thread, one way or another. However, since disagreements are likely inevitable, I put this here rather than in GQ. Mods, feel free to move it if appropriate.

[John_Mace]

The occurance of hurricanes is a statistical phenomenon with many casues-- most of which are either unknown or at least unquantifiable. It would be impossible to say whether any given storm is caused, even in part, by global warming. Rather, one would look at the variations in storm numbers and intensities over time to look for abnoral patterns. Problem is, we really don’t know know what “normal” is…

[Measure_for_Measure]

I don’t see a necessary conflict. It is plausible that the Atlantic Multidecadal Oscillation (AMO) leads to a greater incidence of hurricanes and that higher surface water temperatures lead to a higher intensity.

From National Geographic:

As the conveyor belt speeds up, tropical surface water is drawn north more quickly, and temperatures in the North Atlantic are as much as 2°F warmer. That’s good for hurricanes. “A hurricane is essentially an engine that runs on heat,” says Chris Landsea, a meteorologist at NOAA’s Hurricane Research Division in Miami. “The warmer the sea-surface temperature [it must be at least 80°F for a hurricane to start] and the more warm, moist air that’s available, the stronger a hurricane can become.”

Princeton’s Geophysical Fluid Dynamics Laboratory maintains the following:

Although we cannot say at present whether more or fewer hurricane will occur in the future with global warming, the hurricanes that do occur near the end of the 21st century are expected to be stronger and have significantly more intense rainfall than under present day climate conditions. This expectation (Figure 1) is based on an anticipated enhancement of energy available to the storms due to higher tropical sea surface temperatures.

[Loopydude]

To echo the above, I think it’s impossible to quantify the imact of global warming on any single hurricane. It is possible to see trends historically, and extrapolate the impact of global warming on future storm intensities, in terms of averages, using climate modeling.

Here is another link on the subject.

[DSeid]

The Union of Concerned Scientists has the same take. More severe hurricanes even though unknown if greater or less in number.

The other bit is more extremes in climate variability. To many ecosystems (and their contingent economies) this is likely to have a larger impact than the absolute temperature rise. I had always put hurricanes in that extremes grouping - the big is bigger, the bad, badder.

[Measure_for_Measure]

I’ve always found it interesting that the states that would be hit worst by global warming -Louisiana and Florida- don’t seem to care that much about it.

Then again, shifts in precipitation patterns might not make farmers too happy either.