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Monday, 30 March 2009 19:12

Dust, not climate warming, main cause of Atlantic temp increase

According to a U.S. study performed at the University of Wisconsin, about 70% of the recent warming trend in the Atlantic Ocean is from reduced numbers of dust storms and volcanic eruptions. Other factors, such as a warming of the global climate, contribute only about 30% to the upward trend.

The paper by Amato T. Evan (University of Wisconsin [UW], Madison), along with Daniel J. Vimont (UW), Andrew K. Heidinger (NOAA),  James P. Kossin (NOAA/NESDS/National Climatic Data Center), and Ralf Bennartz (UW), was published in the journal Science.

Appearing in the online issue on March 26, 2009, the title of the paper (DOI: 10.1126/science.1167404) is “The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies.”

Leading the research team is Dr. Evan, from the Cooperative Institute for Meteorological Satellite Studies and the Department of Atmospheric and Oceanic Sciences, both at UW.

The research team states in the abstract to their paper, “Observations and models demonstrate that northern tropical Atlantic surface temperatures are sensitive to regional changes in stratospheric volcanic and tropospheric mineral aerosols.”

Aerosols are defined as the suspension of solid or liquid particles in a gaseous medium.

In Earth’s atmosphere (the gaseous medium, including nitrogen, oxygen, argon and other gases), such suspended (airborne) solid or liquid particles include dust, pollen and spores, sea spray, various industrial pollutants, and other such materials.

The authors added that before their study is was, “… unknown if the temporal variability of these aerosols is a key factor in the evolution of ocean temperature anomalies.”

Page two adds more detail to this research study.

Because of this uncertainty about aerosols as a primary factor in ocean temperatures, the research team used historic satellite date from the past 26 years, along with current climate models, to develop a new physical model of the ocean’s temperature.

Their aim was to estimate the Atlantic Ocean’s temperature gradient (change) with respect to aerosols (dust particles, etc.) in the atmosphere.

They concluded, “Our results suggest that 69% of the recent upward trend, and 67% of the detrended and 5-year low pass filtered variance, in northern tropical Atlantic Ocean temperatures is the mixed layer’s response to regional variability in aerosols.”

Specifically, surface temperatures of the northern Atlantic Ocean are affected by dust storms from the African continent and volcanic eruption from tropical regions, such as the 1982 eruptions of El Chichón in Mexico and the 1991 eruptions of Mount Pinatubo in the Philippines.

Thus, the study lead by Dr. Evan shows that the reduction of the number of African dust storms and tropical volcanic eruptions accounts for 69% of the warming of the North Atlantic Ocean over the past three decades.

According to the March 28, 2009 ScienceDaily.com article Airborne Dust Reduction Plays Larger Than Expected Role In Determining Atlantic Temperature, “Since 1980, the tropical North Atlantic has been warming by an average of a quarter-degree Celsius (a half-degree Fahrenheit) per decade.”

It adds, “Though this number sounds small, it can translate to big impacts on hurricanes, which thrive on warmer water, says Amato Evan…. For example, the ocean temperature difference between 1994, a quiet hurricane year, and 2005's record-breaking year of storms, was just one degree Fahrenheit.”

Page three concludes with the affect of dust in the air with ocean temperatures and the incidences of hurricanes.

Because of this discovery the Evan team predicts that the lessened state of airborne particles in the atmosphere will produce more and larger hurricanes. In addition, their research should add to a better understanding of the world’s changing climate and weather.

In essence, African dust storms and tropical volcanic eruptions affect the temperature of the North Atlantic oceans with respect to their airborne particles.

Less aerosols in the atmosphere increases the amount of sunlight that impacts the ocean and, thus, warms the waters. More aerosols, on the other hand, decreases the amount of sunlight and cools the waters.

According to ScienceDaily.com “Evan and his colleagues have previously shown that African dust and other airborne particles can suppress hurricane activity by reducing how much sunlight reaches the ocean and keeping the sea surface cool.”

And, “Dusty years predict mild hurricane seasons, while years with low dust activity — including 2004 and 2005 — have been linked to stronger and more frequent storms.”

Evan states. "A lot of this upward trend in the long-term pattern can be explained just by dust storms and volcanoes. About 70 percent of it is just being forced by the combination of dust and volcanoes, and about a quarter of it is just from the dust storms themselves." [ScienceDaily.com]

He adds, "Volcanoes and dust storms are really important if you want to understand changes over long periods of time. If they have a huge effect on ocean temperature, they're likely going to have a huge effect on hurricane variability as well."

The ScienceDaily.com article concludes, “The result suggests that only about 30 percent of the observed Atlantic temperature increases are due to other factors, such as a warming climate."

"While not discounting the importance of global warming, Evan says this adjustment brings the estimate of global warming impact on Atlantic more into line with the smaller degree of ocean warming seen elsewhere, such as the Pacific.”

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