HUMANS 'CAUSING STRONGER STORMS'
Increases in hurricane intensity are down to humanity's greenhouse gas emissions, according to new analysis.
Scientists calculate that two-thirds of the recent rise in sea temperatures, thought to fuel hurricanes, is down to anthropogenic emissions.
Research published last year found there had been a sharp rise in the incidence of category 4 and 5 storms - the strongest - in recent decades.
Actually, sea surface temperatures in our dimension appear to be cooling. And I wouldn't call any of the Atlantic hurricanes this season "intense" at all. There have been intense Pacific hurricanes, but not as many as in previous years.
But other scientists caution there may be errors in historical storm records.
Hurricane formation is strongly linked to sea surface temperature, with warmer waters more likely to form storms.
Sea surface temperature and hurricane strength vary naturally, and deciphering a clear impact of human greenhouse gas emissions has been difficult.
However, the last two years have seen several major pieces of research which have at least increased understanding of the issue, without settling it conclusively.
In July last year, Kerry Emanuel, from Massachusetts Institute of Technology, published research showing that the duration, maximum wind speeds and energy released in tropical storms has increased markedly in both the North Atlantic and the North Pacific oceans since the mid-1970s.
A few months later Peter Webster from the Georgia Institute of Technology documented a rise in the incidence of category 4 and 5 storms; the 15-year period from 1975 to 1989 saw 171 severe hurricanes, but the number rose to 269 for the subsequent 15 years.
He told the BBC News website at the time: "What I think we can say is that the increase in intensity is probably accounted for by the increase in sea surface temperature, and I think probably the sea surface temperature increase is a manifestation of global warming."
Then in June this year, Kevin Trenberth of the US National Center for Atmospheric Research analysed the exceptionally active 2005 North Atlantic hurricane season.
Sea surface temperatures (SST) had been 0.9C above the long-term average, he found; and by comparing the North Atlantic with other regions of the ocean, he deduced that human greenhouse gas emissions accounted for about half of this rise.
Of course, we need to ignore other earth-based research such as Michaels et al. (2006) which says:
“Whereas there is a significant relationship between overall sea-surface temperature (SST) and tropical cyclone intensity, the relationship is much less clear in the upper range of SST normally associated with these storms. There, we find a step-like, rather than a continuous, influence of SST on cyclone strength, suggesting that there exists a SST threshold that must be exceeded before tropical cyclones develop into major hurricanes. Further, we show that the SST influence varies markedly over time, thereby indicating that other aspects of the tropical environment are also critically important for tropical cyclone intensification. These findings highlight the complex nature of hurricane development and weaken the notion of a simple cause-and-effect relationship between rising SST and stronger Atlantic hurricanes. ”
The text of the article includes the statement,
“Our results show that SST plays a relatively minor role in the observed characteristics of tropical storms and hurricanes in the North Atlantic Basin. As such, other factors must be involved in the increase in tropical cyclone activity recorded during the post-1994 Atlantic hurricane seasons. The full reason behind these observed changes remain an area of active scientific inquiry. We therefore recommend a cautious approach to assigning an underlying cause in this complex system.”
The latest research takes things another step further, using 22 computer models of climate to examine a possible link between SSTs and human-induced global warming.Oh boy, COMPUTER MODELS! Now we'll get the real story!
These models typically deal in projections and probabilities, which is inevitable with a huge and chaotic system such as global climate.
And the fact that they are "huge and chaotic" means that the results of these models should be highly suspect. But of course........
Benjamin Santer, Tom Wigley and colleagues conclude: "There is an 84% chance that external forcing [human activities] explain at least 67% of the observed SST increases" in the Pacific and Atlantic zones where hurricanes form.
"The important conclusion is that the observed SST increases in these hurricane breeding grounds cannot be explained by natural processes alone," said Dr Wigley.
"The best explanation for these changes has to include a large human influence."
Why isn't the best explanation that there is a lot of natural variability in SSTs and we really don't know what causes it? Why does "human influence" have to be the default explanation for any change in the climate system that we can't immediately explain?
[I have omitted some objections from "skeptics" (i.e. "actual scientists") which point out the obvious - the very short period of time that accurate hurricane records have been kept and surely the understatement of the year, that "computer models are far from perfect"]
But as Benjamin Santer and Tom Wigley point out, what other tools are there for projecting the future?
Well, there are chicken entrails. The ancients had some luck with those. Or maybe Santer and Wigley should invest in a huge crystal ball and some Tarot cards. I hear that the "Psychic Friends" have more reasonable rates these days. Any of these methods would be just as accurate and probably much cheaper than all those computer models. And they would also be able to give S & W valuable information on their future with the ladies.
"In the real world, we are performing an unprecedented and uncontrolled geophysical experiment," they write. "We know, beyond a shadow of doubt, that [human] activities have changed the chemical composition of the Earth's atmosphere.
Well, I'm glad to see that they've noticed SOME difference between computer models and the real world. The chemical composition of the Earth's atmosphere (real world again) has been profoundly changed in the past by plant activity (where that 20% O2 came from), volcanic activity (probably where the original atmosphere came from), and other natural forces (where the vast majority of the atmospheric CO2 comes from).
"In a post-Katrina world, we need to do the best job we possibly can to understand the complex influences on hurricane intensity."
Why drag Katrina into this? It was only a Category 3 when it made landfall. The destruction and loss were truly tragic, but more due to people's land use and other decisions than the severity of the storm. Wouldn't it be better and more effective to recognize the dangers inherent in living near the Atlantic and Gulf coasts and actually have a plan for dealing with hurricanes?
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