WASHINGTON - A new research by NASA scientists has suggested that much of the atmospheric warming observed in the Arctic since 1976 may be due to changes in tiny airborne particles called aerosols.

Emitted by natural and human sources, aerosols can directly influence climate by reflecting or absorbing the sun’s radiation.

The small particles also affect climate indirectly by seeding clouds and changing cloud properties, such as reflectivity.

A new study, led by climate scientist Drew Shindell of the NASA Goddard Institute for Space Studies, New York, used a coupled ocean-atmosphere model to investigate how sensitive different regional climates are to changes in levels of carbon dioxide, ozone, and aerosols.

The researchers found that the mid and high latitudes are especially responsive to changes in the level of aerosols.

Indeed, the model suggests aerosols likely account for 45 percent or more of the warming that has occurred in the Arctic during the last three decades.

Though there are several varieties of aerosols, previous research has shown that two types - sulfates and black carbon - play an especially critical role in regulating climate change.

Both are products of human activity.

Over the past three decades, the United States and European countries have passed a series of laws that have reduced sulfate emissions by 50 percent.

At the same time, black carbon emissions have steadily risen, largely because of increasing emissions from Asia.

Black carbon - small, soot-like particles produced by industrial processes and the combustion of diesel and biofuels - absorb incoming solar radiation and have a strong warming influence on the atmosphere.

In the modeling experiment, Shindell and colleagues compiled detailed, quantitative information about the relative roles of various components of the climate system, such as solar variations, volcanic events, and changes in greenhouse gas levels.

The regions of Earth that showed the strongest responses to aerosols in the model are the same regions that have witnessed the greatest real-world temperature increases since 1976.

The Arctic region has seen its surface air temperatures increase by 1.5 degree Celsius since the mid-1970s.

In the Antarctic, where aerosols play less of a role, the surface air temperature has increased about 0.35 degree C.

That makes sense because of the Arctic’s proximity to North America and Europe.

The two highly industrialized regions have produced most of the world’s aerosol emissions over the last century, and some of those aerosols drift northward and collect in the Arctic.

According to Shindell, “It appears that aerosols have quite a powerful effect on climate.” (ANI)