Posted on 06/27/2006 9:34:22 AM PDT by cogitator
BOULDER, Colorado, June 26, 2006 (ENS) - Global warming created about half the extra warmth in the waters of the tropical North Atlantic that stimulated hurricane formation in 2005, while natural cycles were a minor factor, a new study from the National Center for Atmospheric Research demonstrates.
The research by world leading climate scientists contradicts recent claims that natural cycles are responsible for the increase in Atlantic hurricane activity since 1995 and adds support to the theory that hurricane seasons will become more active as global temperatures rise.
While researchers agree that the warming waters fueled hurricane intensity, they have been uncertain whether Atlantic waters have heated up because of a natural, decades-long cycle, or because of global warming.
The new analysis by lead author Dr. Kevin Trenberth and associate scientist Dennis Shea of the National Center for Atmospheric Research (NCAR) will appear in the June 27 issue of "Geophysical Research Letters," published by the American Geophysical Union.
"The global warming influence provides a new background level that increases the risk of future enhancements in hurricane activity," says Trenberth, who heads NCAR's Climate Analysis Section.
Last year produced a record 28 tropical storms and hurricanes in the Atlantic. Hurricanes Katrina, Rita, and Wilma all reached Category 5 strength, the highest level on the Saffir-Simpson Hurricane Scale. Category 5 hurricanes carry winds greater than 155 mph (249 km/hr). The storm surge is greater than 18 feet (5.5 meters) above normal.
This year the National Weather Service Climate Prediction Center forecasts a "very active" season, with 13-16 named storms, 8-10 hurricanes, and 4-6 major hurricanes.
The 2006 prediction indicates a continuation of above-normal Atlantic activity that began in 1995, but forecasters say they do not currently expect a repeat of last year’s record season.
Trenberth and Shea's research focuses on an increase in ocean temperatures.
During much of last year's hurricane season, sea-surface temperatures across the tropical Atlantic between 10 and 20 degrees north, where many Atlantic hurricanes originate, were a record 1.7 degrees Fahrenheit above the 1901-1970 average.
By analyzing worldwide data on sea-surface temperatures since the early 20th century, Trenberth and Shea were able to calculate the causes of the increased temperatures in the tropical North Atlantic.
Their calculations show that global warming explained about 0.8 degrees F of this temperature rise.
Aftereffects from the 2004-05 El Nino accounted for about 0.4 degrees F.
The Atlantic multidecadal oscillation (AMO), a 60 to 80-year natural cycle in sea-surface temperatures, explained less than 0.2 degrees F of the rise, Trenberth says.
The remainder is due to year-to-year variability in temperatures.
Earlier studies have attributed the warming and cooling patterns of North Atlantic ocean temperatures in the 20th century - and associated hurricane activity - to the Atlantic multidecadal oscillation.
But Trenberth, suspecting that global warming is also playing a role, looked beyond the Atlantic to temperature patterns throughout Earth's tropical and midlatitude waters.
He subtracted the global trend from the irregular Atlantic temperatures - separating global warming from the Atlantic natural cycle.
The results show that the AMO is weaker now than it was in the 1950s, when Atlantic hurricanes were also active.
However, the AMO did contribute to the lull in hurricane activity from about 1970 to 1990 in the Atlantic.
Global warming does not guarantee that each year will set records for hurricanes, according to Trenberth. He notes that last year's activity was related to very favorable upper-level winds as well as the extremely warm sea-surface temperatures.
Trenberth says each year will bring ups and downs in tropical Atlantic sea-surface temperatures due to natural variations, such as the presence or absence of El Nino, a warming pattern in the tropical Pacific Ocean.
Still, the researchers conclude that over the long-term ocean warming will raise the baseline of hurricane activity.
There is an assumption here that Global Warming is one thing, and "natural cycles" are another thing. I need to read no further.
There. I fixed it.
The .edu on the end of the URL says it all.
Nothing to see here, move along.
And Dr. William Gray, who is the preeminent hurricane expert in this country, has said that so called global warming has nothing to do with Atlantic hurricanes.
"Global warming" is generally used to indicate the warming of the globe that has occurred since the mid-1800s. There is considerable scientific evidence that this warming, particularly the warming which occurred in the late 1980s into the 1990s and to present, has been augmented by human activities, particularly those that add CO2 to the atmosphere. CO2 concentration in the atmosphere has increased about 100 ppm since the mid-1800s, and this is about 100 ppm higher than the natural maximum over the past 640,000 years, as determined from measurements of CO2 in ice core bubbles.
Feel free to continue thinking that global warming is entirely natural. The scientific data does not support that line of thinking.
If you're happy with it, then I won't attempt to disturb your mindset.
It was the last time it happened.
Dr. Gray is not an oceanographer, and some of his ideas about oceanography are pretty clearly wrong.
Gray and Muddy Thinking about Global Warming
Now, this article doesn't directly address what Dr. Gray knows about hurricanes. But the new study just came out, and requires evaluation. Dr. Gray's evaluation will be one of many.
Please explain for the class how the Vikings made the world warm, how the Pilgrim caused things to get cold, and how Abe Lincoln managed to heat things up again.
It's a natural cycle.
And I'll bet the CO2 in ice core bubbles doesn't degrade one little bit being in contact with all that frozen and often liquid H2O for all that millenia, no sirree. Can you insure that those ice cores came from glaciers in which no liquid water occured in the time the CO2 was trapped?
... which causes cooling. Every model I have looked at shows that concentrated convection causes cooling. The subsidence around hurricanes cools and is much larger than the hurricane itself. Another factor is that tropical convection (not just hurricanes) peaks at night and therefore so do the cold cloud tops which warm the planet. There are probably other factors, but basically this increase in storminess is a sure sign of negative feedback from warming oceans.
Not one hurricane hit Florida from 1952 to 1962, a period of high water temperature the study references.
Higher water temps alone are not reliable predictors of frequency or severity.
Subtracting higher water temperatures elsewhere from the measured data guarantees the remaining increase will not be attributable to the rest of the factors the study includes.
What sort of science is this?
All of the effects that you mention have been evaluated. The current warming trend is being augmented by the increasing concentration of CO2 in the atmosphere. Natural variability cannot account for all of the observed warming.
I can back up all of these statements with references to scientific literature, if you would be willing to consider what they say. From long experience, I know that this effort is usually fruitless for someone who already has their mind made up. Tell me if you're actually interested -- I won't waste my time or yours if you aren't.
Why should it degrade? The ice cores are from Greenland or Antarctic ice caps. If you want to know more, try searching on the subject. I have extreme confidence that the CO2 concentrations measured in ice core bubbles are accurate, because they've been independently determined from more than one ice core.
Atmospheric or oceanic surface cooling?
We can just agree to disagree, since I consider that scientific literature to be agenda-driven crap. I grant that temperatures are rising. I grant that CO2 levels are rising. I laugh at the idea that humans are changing the global climate.
Does that indicate that the 1950s weren't an active hurricane period? It can be an active period and yet still spare Florida.
Higher water temps alone are not reliable predictors of frequency or severity.
What sort of science is this?
Published. It's in Geophysical Research Letters.
I agree.
Not completely sure but probably oceanic surface from the lack of clouds. The other effect is the removal of water vapor from the upper troposphere reducing the atmospheric warming.
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