Contrary to popular belief, cleaner air could actually make global warming much worse than its current state, two new studies revealed.
In fact, a large part of greenhouse gas-induced climate change has been hidden from us in the past by another type of pollution. The spotlight is on the effect of aerosol - particles released by industrial activity - on the Earth's climate.
Apparently, aerosol pollution temporarily counters the warming and cools the climate. But as nations all over the world attempt to reduce aerosol pollution in the air, researchers of both studies suggest the world will see more rapid warming. This could hinder our ability to meet the goals set during the landmark climate agreement in Paris last December 2015.
How Aerosol Affects The Atmosphere
Experts said certain types of aerosol emissions cause a strange cooling effect to the climate by blocking solar radiation from reaching the surface of our planet. Emissions such as sulfate either help increase the reflectivity and extent of cloud cover over the Earth or scatter sunlight directly.
Areas where pollution is heaviest experience the cooling effect more, momentarily masking the continuous warming produced by greenhouse gases in the atmosphere. Aerosols, however, have a short life span in the atmosphere. Precipitation eventually clears them out of the sky.
Scientists believe that if human activity is constantly pouring aerosol pollution into the air, then the strange cooling effect would probably be sustained.
Now that certain parts of the world are reducing their aerosol emissions, a peculiar phenomenon called "regional brightening" has been observed. Basically, the dimming and cooling effect of aerosol accumulation is beginning to lift away.
Reducing Aerosol Emissions In Europe
One of the two new studies said regional brightening already has an impact on certain parts of the planet.
The paper examined the effect of European reductions of aerosol emissions on warming in the Arctic. Europe has actually lessened its aerosol emissions the most in the previous years compared to the rest of the Earth's regions.
Because of that, scientists found that the Arctic warming is occurring at a faster rate than that in the other parts of the world. The continent's policies most likely have the biggest effect on aerosol-related climate change.
How did the research team find that out? They used climate model simulations that took into account the changes in aerosol emissions. They conclude that as much as 0.5 degrees Celsius (32.9 degrees Fahrenheit) of the Arctic warming between 1980 and 2005 is because of the aerosol reductions in Europe during those periods.
As the Washington Post puts it, the aerosol "mask" is being lifted away, and scientists are beginning to see regional warming as a result.
But why does it have such a huge effect? Thorsten Mauritsen, an expert who wrote an accompanying commentary for the first study, said it has something to do with the atmospheric and oceanic currents that run between the Arctic and Europe.
"Europe is situated right on the main pathway that air and ocean currents take from more southerly latitudes into the Arctic," said Mauritsen, who is from the Max Planck Institute for Meteorology.
Mauritsen said the warming of the upper ocean and the atmosphere during the summer through reduced cooling around Europe results in the stronger transport of heat into the Arctic, which is actually "pristine" in general. So aerosols that drift up there from Europe likely had a more noticeable cooling effect than in other regions of the world. When the aerosol accumulations rained back down on Earth, there was a pronounced increase in warming as well.
The Significance Of Aerosol On A Global Scale
The second study meanwhile looked at how aerosol emissions impact the Earth's temperature through a phenomenon the researchers call "transient climate sensitivity," or how much of the Earth's temperature will change when the amount of carbon dioxide in the atmosphere reaches twice its level during the pre-industrial times.
Long story short: because aerosol emissions "masked" a great amount of warming, some scientists believe that estimates of our planet's transient climate sensitivity are too low, and that climate may be more sensitive to carbon emissions than what we know. This could lead to greater warming in the future, researchers said.
Trude Storelvmo of Yale University and her colleagues did not use climate models to find out the answer, but they based their calculations on temperature and solar radiation records taken from more than thousands of global measurement sites over the course of 46 years.
The team found that 74 percent of the warming that occurred during 1964 to 2010 was indeed masked by the aerosol cooling effect. Taking it into account, they then calculated the Earth's climate sensitivity and found that whenever CO2 levels doubled, we should see an increase in temperature of about 2 degrees Celsius (35.6 degrees Fahrenheit) above pre-industrial levels.
Storelvmo said other studies may have underestimated the influence of aerosols on the climate. She said their findings have the implication that we can't allow for CO2 doubling to ever happen, and that the higher the transient climate sensitivity is, the lesser fossil fuels should be up in the air.
Both papers are featured in the journal Nature Geoscience.
How About The Effects Of Acid Rain And Smog?
Of course, this does not mean that aerosols such as sulfur dioxide do not have negative effects on the environment.
Acid rain, which is the type of rain that possesses high levels of hydrogen ions, still has noxious and vile effects on streams, lakes, forests, aquatic animals, infrastructure and plants.
Smog, which is typically the result of a mixture of smoke and sulfur dioxide, continues to plague Beijing, New Delhi, Hanoi and other cities all over the world.
Some scientists are looking into methods to release aerosol particulates high into the atmosphere to help us find time to implement more effective greenhouse gas reductions. The particulates may also temporarily act as aerosol masks in the atmosphere.
However, they are also still mapping out the association between pollution, climate and weather, and one particular concern is that injecting aerosol into the atmosphere without a thorough understanding of the process might just make things worse.
Photo: Eric Golub | Flickr