Reduction of greenhouse gases and their aerosols – what could go wrong?

There is good news. Globally, man-made greenhouse gases are declining, perhaps not as much as we would like to see, but they are declining nonetheless. Now for some counterintuitive and bad news. The aerosols associated with these man-made greenhouse gases are also decreasing, but their reduction is accelerating global warming. What about it?

Some background

Climate forcing – “the difference between the rate of energy received by absorption of solar radiation and the rate of energy emitted by the top of the Earth’s atmosphere, expressed in watts per square meter (W m^{− 2})”

• Our climate reflects the balance between absorption and reflection of solar radiation.
• Clouds and aerosols reflect solar radiation.
• Greenhouse gases (GHG), ozone and water vapor absorb radiation.
• Snow and ice on the earth’s surface reflect the sun’s radiation – a high Albedo Effect. Darker areas of the world, especially the tropics, absorb solar energy and have a low albedo effect.

There are several forces affecting the climate depicted here.

• Other anthropogenic influences are aerosols created by human activities – a suspension of fine particles such as particulate matter_2.5Black carbon (organic carbon) and chemicals formed in the atmosphere such as SO_2.
• Natural forcings include clouds, wildfires, and especially volcanic eruptions. Both produce aerosols

There is a further entanglement when considering the balance between positive climate forcing (GHG) and negative climate forcing (aerosols), their lifetimes and sources. Greenhouse gases persist in the environment, accumulating over time, making their sources relatively insignificant. On the other hand, aerosols are short-lived, days not years, and they do not accumulate at the same rates as greenhouse gases. Their spatial and temporal sources are more critical. Due to longevity and spatio-temporal differences, there is a dynamic balance between the two that, along with a variety of other factors, explains the variability of our daily climate.

What did the researchers find with some context?

“…without the cooling effects of aerosols, the world would have already reached the 1.5°C temperature threshold of ‘dangerous’ climate change set out in the Paris Agreement.”

The research used satellite data from 2000 to 2019 and modeling for periods before that to examine the presence of greenhouse gases and aerosols.

• Since 1750, CO2 has been responsible for a temperature rise of 1:01°C; all greenhouse gases contributed to a total increase of 1.81 °C. Aerosols lowered the temperature by 0.50 °C over the same period
• Aerosol production has been declining in Europe and North America since 1980 and in China since 2010.
• Aerosols produced over the oceans come from the sea spray and fuel used in shipping. Since 2010 there has again been clear evidence that shipping-related aerosol production has declined.
• Aerosols do not accumulate, which is why the frequency of aerosols has also decreased. The only area of ​​increased aerosol accumulation is over India.

Overall, the global impact of man-made aerosols on the climate has decreased. Remember that aerosols cool the atmosphere, so our reduction in man-made aerosols, a by-product of our synchronous reductions in greenhouse gases, additionally warms up our environment. There it is. The unintended consequence of our quest to rid the atmosphere of greenhouse gases. The researchers estimate that our reduction in aerosols has contributed between 15% and 50% to global warming since 2000.

Sources: Climate Forcing Copernicus

Robust Evidence for Trend Reversal in Aerosol Effective Climate Forcing Atmospheric Chemistry and Physics DOI: 10.5194/acp-22-12221-2022