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A trio of atmospheric and climate specialists at the University of Melbourne, has found evidence showing that the high amount of smog over some mega-cities may be temporarily protecting them from feeling the threat of global warming. In their , reported in the journal Geophysical Research Letters, Aditya Sengupta, Andrew King and Robert Ryan studied the rates of warming in several global regions and found that not all areas are experiencing the same heat increases.

Though it is commonly accepted that rising CO₂ levels are heating the atmosphere, climate scientists disagree on the rate of increase—some suggest the world is on the same path that has been predicted for years, with increased rates of greenhouse gases tied with rates of warming.

Others disagree, suggesting that feedback loops, unknown sources of greenhouse gas emissions and other factors indicate that the rate of warming is increasing faster than current models suggest. Many also suggest that the planet is heading toward a tipping point at which the planet continues to grow warmer—perhaps too warm for most life to survive.

In this new effort, the researchers found evidence that some major cities are experiencing a temporary reprieve from such increases in temperature due to aerosol particles in the air, such as soot, that block sunlight and heat, protecting cities with dirty air from current increases.

They came to this conclusion by comparing the rates of heat increases for several global regions and found that major cities with dirty air, such as Mumbai and Cairo, have been experiencing slower rates of increase than areas around them and other cities of similar size but with cleaner air.

The researchers suggest such protection is temporary however, as history has shown that as cities modernize, they reduce such emissions, resulting in cleaner air and a clearer sky that will allow more heat to reach the surface.