Cause studied in ocean warming

The area where hurricanes form in the tropical Atlantic may be getting warmer due to human impact, according to new research released this week.

BY HEATHER MOYER | BALTIMORE | May 4, 2006


The area where hurricanes form in the tropical Atlantic may be getting warmer due to human impact, according to new research released this week.

Scientists at the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Fluid Dynamics Laboratory (GFDL) released a study this week that suggests that human activity, such as increasing greenhouse gas emissions into the atmosphere, may contribute to the increasing sea-surface temperatures in one hurricane-producing part of the Atlantic Ocean.

"There does appear to be a warm trend emerging in the tropical Atlantic and our models infer that there is an anthropogenic influence on it," said Dr. Thomas Knutson, the study's lead author and research meteorologist for the GFDL.

"We've known there has been a lot of evidence around already that global temps were increasing. We were looking more on regional scales. This study sort of broadly looks at various regions around the globe."

This hurricane-producing area of the Atlantic is near the Cape Verde Islands off the coast of Africa and is known as the "Main Development Region."

Knutson said the difference between their study and past ones not demonstrating an influence is that his team looked at sea surface temperatures over the past century.

Shorter durations make seeing variability more difficult because of regular multi-decadal cycles, he added, and the Atlantic was not showing much warming over the past 50 years.

Knutson also cautioned that these results do not equate with having more hurricanes each season. "We're just talking sea surface temperatures here. We need more work to sort of pin down exactly what the implications are for hurricanes. There are more influences besides sea surface temperatures on hurricanes."

He also clarified the research's impact in a NOAA news release.

"This very long-term increase in temperature may seem small but is comparable in magnitude to shorter time-scale, multi-decadal changes that many scientists now believe contribute strongly to an increase in hurricane activity in the Atlantic," said Knutson.

"The challenge is to understand the relative roles of anthropogenic and natural factors in producing these temperature changes and this study is a step in that direction and then to determine whether and how these long-term changes in temperature could be affecting Atlantic hurricane activity."

A new atmosphere-ocean model developed by the GFDL helped produce the climate model simulations for this study. The new simulations include improved representations of a number of environmental factors that can affect climate, such as greenhouse gases, volcanic eruptions, solar variability, land-use changes and atmospheric aerosols, very fine particulate matter in the air.

The study's model simulations used current best estimates of a number of historical climate data to simulate climate variations over the 20th century. In the Main Development Region, the observed warming during the 20th century is simulated much more realistically in the models that include anthropogenic impact than in models with only natural effects.

Other sources of anthropogenic influence include aerosols and land-use changes. Some examples of natural effects are volcanic emissions, long-term variability of solar radiation, and internal variability, such as the internal processes within the climate system.

The GFDL study also included results on temperature variations in other oceans. Knutson said one region of the Indian Ocean has been warming consistently over the past 50 years - and that's been easier to observe than the Atlantic region's warming.

He also noted that these changes in temperatures are just occurring in certain areas of the oceans - not over the entirety of the bodies of water. "There are some regions where no warming has happened. The southeast U.S. area has not even been warming over the period we looked. There are unusual regions of the globe not showing a warming trend over the century."


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Related Links:

National Oceanic and Atmospheric Administration

NOAA Geophysical Fluid Dynamics Laboratory

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