African Dust Heats Up Atlantic Tropics

The evidence is in, observations and models show that northern tropical Atlantic surface temperatures are sensitive to dust blowing in from North Africa. Regional changes in stratospheric volcanic and tropospheric mineral aerosols (i.e. dust) are responsible for 69% of the upward trend in temperatures over the last 30 years. Once again a new factor has been discovered that is not accounted for in general circulation models (GCM) used to predict global warming—and once again the importance of CO2 is diminished.

A new study, based on 26 years of satellite data, has uncovered the importance of airborne particles in the warming of the surface waters of the northern tropical Atlantic ocean. A joint effort by scientists at the University of Wisconsin and the US National Oceanic and Atmospheric Administration (NOAA) concludes that the majority of the sharp temperature rise seen over the past three decades in the tropical Atlantic is due to dust blowing out to sea from the deserts of Northern Africa.

Massive sandstorms blowing off the Northwest African desert can blanketed hundreds of thousands of square miles of the eastern Atlantic Ocean with dense clouds of Saharan sand. The image below shows one such massive storm that was first seen in February 26, 2000, when it reached over 1000 miles into the Atlantic.

These storms can lift dust 15,000 feet or more above the African deserts where it then blows out across the Atlantic. Many times the dust from these storms has reached as far as the Caribbean, causing local weather services to issue air pollution alerts. Recent studies by the US Geological Survey (USGS) have linked the decline of the coral reefs in the Caribbean to the increasing frequency and intensity of Saharan Dust events. Additionally, other studies suggest that Sahalian Dust may play a role in determining the frequency and intensity of hurricanes formed in the eastern Atlantic Ocean. Both of these events, dying coral and hurricanes, have been blamed on global warming by climate change activists.

Since 1980, tropical North Atlantic Ocean temperatures have been rising at a rate of nearly 0.45°F (0.25°C) per decade. Past studies have attributed this increase, explicitly and implicitly, to global warming but these studies fail to provide either a mechanism for or direct evidence of how these variables control tropical North Atlantic Ocean temperatures. In a paper published in Science, titled “The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies,” Amato T. Evan, Daniel J. Vimont, Andrew K. Heidinger, James P. Kossin, and Ralf Bennartz document this important finding.

The maps shown below illustrate the linear trends in observed sea surface temperature (SST) on the left and the residual SST after subtracting the effect of the aerosols on the right. Trends are calculated from the annual mean time series at each 0.5° grid cell over the 1982–2007 period. Hatched areas represent regions with linear trends that are statistically significant at the 95% level. The area enclosed by thick black lines (i.e., the oceanic regions of 0° to 30°N and 15° to 65°W) represents the region over which mean time series are calculated, and in (B) is the area where the aerosol direct effect and its impact on ocean temperatures have been estimated.

Notice how some areas of the ocean that are warming because of the airborne dust would be actually cooling without it. Yet some climate “experts” would attribute the warming ocean waters to greenhouse gases. Because the effects of airborne particulates have been poorly understood they are not correctly accounted for in GCM models. This means that when climate modelers adjusted their models to reproduce known conditions, a process called calibration, they had to distort the contributions of other factors to make up for the missing aerosols. In other words, their models are biased and wrong. Quoting from the paper:

Over the past 30 years, temperatures in other tropical ocean basins have been rising steadily, but at a slower rate than in the Atlantic. At the same time, projections of surface temperature increases under a doubled carbon dioxide climate suggest that the Atlantic should be warming at a rate slower than the other observations. We suggest that this apparent disconnect between observations and models may be due to the influence of Atlantic dust cover. Our results imply that because dust plays a role in modulating tropical North Atlantic temperature, projections of these temperatures under various global warming scenarios by general circulation models should account for long-term changes in dust loading

Dust from the Sahara Desert in Africa may also modify clouds and rainfall both in Africa and across the tropical North Atlantic as far away as Barbados, according to a study that uses data from NASA satellites, ground measurements, and computer models. Natalie Mahowald, a scientist at the National Center for Atmospheric Research (NCAR) and University of California, Santa Barbara, and Lisa Kiehl, a graduate student at UCSB, published their findings in a recent issue of Geophysical Research Letters.

“The interaction between clouds and aerosols is critical for understanding climate change,” says NCAR's Mahowald. Clouds play a pivotal role in reflecting and absorbing the Sun's rays, as well as radiation emitted from Earth's surface. This NASA funded study was the first long-term regional study to confirm observations that mineral aerosols can act as kernels for precipitation to form around. It is also the first to suggest that African dust interacts with clouds over a large region.

Space Shuttle astronauts frequently track Saharan dust storms as they blow from north Africa across the Atlantic Ocean. Dust palls blowing from Africa take about a week to cross the Atlantic. The upper picture at the right looks Southwest over the northern edge of a large trans-Atlantic dust plume that blew off the Sahara desert in Africa. In this view, Caicos Island in the Bahamas and the mountainous spines of Haiti are partly obscured by the dust. Closer to the foreground, (about 26 degrees north latitude), the skies are clear.

The lower photograph was taken by Shuttle astronauts while docked to the International Space Station on August 19, 2001. The boundaries of the dust plumes can be traced visually by the abrupt change from clear to hazy atmosphere—the hazy line marks the northern edge of the dust cloud near the Caribbean.

It's amazing that something seemingly as simple as dust in the air can have such varied and widespread impacts on the world we live in. Even more amazing is that the IPCC and other climate change fanatics could ignore the affect of aerosols in their rush to bolster claims of runaway global warming and to place the blame on anthropogenic greenhouse gases. Science does not always come up with correct answers in its first attempt to explain some aspect of nature but, over time, the true facts tend to surface. It is not a sin to propose an incorrect theory, but it is a great sin to cling to that theory in the face of ever mounting evidence that it is wrong.

Be safe, enjoy the interglacial and stay skeptical.