Climate Change Pushing Tropics Farther, Faster

[LJR]

Climate Change Pushing Tropics Farther, Faster

Richard A. Lovett for National Geographic News

December 3, 2007
Over the past 25 years the tropics have expanded by as much as 300 miles (500 kilometers) north and south—evidence of climate change in action, a new study says.

This not only means that rain-drenched regions near the Equator are growing, experts say, but also that global warming may be pushing deserts poleward in places such as the U.S. Southwest, Mexico, Australia, South Africa, South America, and the Mediterranean.






(See a map of where global warming will hit the hardest.) See link at bottom of page
"The rate of increase is pretty big," said study lead author Dian Seidel of the National Oceanographic and Atmospheric Administration's (NOAA) Air Resources Laboratory in Silver Spring, Maryland.

"It's several degrees of latitude over the course of 25 years."

Tracking Air Circulation
If it sounds strange to think of the tropics as expanding, that's because geographers and climate scientists view them differently. To mapmakers, the tropics are simply the regions between 23.5 degrees north and south latitude, where at least once a year the sun is directly overhead.

But Seidel and her team based their definition of the tropical belt on air circulation.

Near the Equator, moist air rises, producing clouds and ideal conditions for rain forests.

That air then moves poleward—north in the Northern Hemisphere, south in the Southern Hemisphere.

Wrung dry of moisture, the air eventually descends back to Earth, producing deserts. Surface breezes then angle back toward the Equator, completing the cycle.

Seidel's team used meteorological and satellite data to find the northern and southern edges of this zone, mapping changes from the late 1970s to the present.


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[Matt-hurricanewatcher]

No its not, because the whole of earth had a below avg year so far. The Atlantic had one of the slowest hurricane seasons of the pass 40 years, with the eastern Pacific. How is it pushing farther and faster? It makes no sense.

Yes, a innerglacieral period has a warmer Atmopshere=warmer oceans. Which can help fuel the hurricanes. But this year even with a la nina that should of brought lighter shear, we seen very little.

Bs also to the fact that the tropics are growing. How do they have the record to prove that?

[HURAKAN]

The expansion is because we have better satellites and the coverage of the entire planet (specially in the Southern Hemisphere), and a better understanding of tropical cyclones. Moreover, in the Atlantic we are naming and/or recognizing more subtropical storms than ever before.

I hate when these studies mislead the public in such a way. Global Warming is occurring, we know that, but don't make it so overwhelming that almost sounds bullish.

[Squarethecircle]

Expansion is occurring, is my view, but not at a particularly dangerous rate; tropics can actually be good for the world, especially because of the large amounts of moisture they can harbor. Not all of GW's effects are supposed to be harmful anyway.

[MGC]

Humanity needs a warmer Earth to provide an enviroment to grow food. GW is a far better alternative than an ice age......MGC

[JonathanBelles]

I would have to agree that expansion is occuring in PART to GW. The other part is as Sandy said, that we have better technology. I also believe that in the next few hundred years, or however long GW lasts, that the hurricane season will get longer and longer with more warmth and warmer water temps. What the effect on shear will be, I dont know. Global warmth must exceed the rate of shear growth in order to produce wider tropical basins and longer seasons.

[Ed Mahmoud]

I get National Geographic at home. They are huge on the Global Warming thing, and about half the articles and stories have a GW theme or connection.


Maybe they are right. Maybe not, but judging from the letters to the editors, they are giving their readers what they want.

[Category 5]

No its not, because the whole of earth had a below avg year so far. The Atlantic had one of the slowest hurricane seasons of the pass 40 years, with the eastern Pacific. How is it pushing farther and faster? It makes no sense.

By no means would I call it one of the slowest seasons in the last 40 years. Yes, the ACE was extremely low for 14 storms, but you gotta look at the bigger picture. Compare it to say 1983, 1997, and I'll throw in 2006. This year had some destructive and historic storms, and considerably more then those other 3 seasons, and many more seasons in the last 40 years, we'll see if we have any unnamed storms as well.

However, you are half right, as I said, the ACE was lower then the average attendence to a Florida Marlins game.

[Sanibel]

Could also be responsible for December storm trend.

[Squarethecircle]

There is no December storm trend; just active years.

[Sanibel]

Ah, ha.

[HURAKAN]

Ah, ha.

I think the increase in technology and the active phase we're going through is the most likely answer to the "increase in December storms."

Storms like Peter in 2003, Zeta in 2005, and Lili in 1984 were most likely missed as non-tropical systems in the pre-satellite era.

[Squarethecircle]

But it does turn out that, even in a record-breaking active cycle, there's less than one storm post-season on average. So even with the satellites there wouldn't be any need to extend the season.

[Frank2]

An almost year-round Atlantic hurricane season might be something that is very possible, similar to the Western Pacific...