Emitted by natural and human sources, tiny airborne particles called aerosols can directly influence climate by reflecting or absorbing the sun's radiation. The small particles also affect climate indirectly by seeding clouds.

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.

They found that the mid and high latitudes are especially responsive to changes in the level of aerosols. Indeed, the model suggests aerosols possibly account for 45 percent or more of the warming in Arctic over the last three decades.

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

Sulphates, which come primarily from the burning of coal and oil, scatter incoming solar radiation and have a net cooling effect on climate. Over the past three decades, the US and European countries have passed a series of laws that have reduced sulphate 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.

The regions 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.

That makes sense, Shindell explained, because of the Arctic's proximity to North America and Europe. The two highly industrialized regions have produced most of the world's aerosol emission, said a NASA release.

The results were published in the April issue of Nature Geoscience.