The aerosol double whammy

The climate scientist Stephen Schwartz describes what he calls the double whammy effect of aerosols on climate change. By reflecting sunlight, and cooling the planet, aerosols don't just mask warming from greenhouse gases, they mask climate sensitivity. Since we don't know how much aerosols cool the planet, we can't tell how sensitive the earth is to changes in energy input, and it's therefore hard to predict what could happen if industrial aerosols, such as sulphur dioxide, are eliminated. It could be much worse that we first thought.

What happens to earth's temperature if we eliminate all aerosols?

No one knows

Aerosols reflect sunlight, counteracting the effect of greenhouse gases. But no one knows how much they reflect.

And that means we don't know the earth's climate sensitivity.

Greenhouse gases warm the planet by adding energy to the atmosphere. This is known as forcing. Climate sensitivity is how much the temperature rises per unit of forcing.

Calculating climate sensitivity should be a simple matter of dividing change in temperature by change in energy.

For example, we know how much the earth's temperature has increased in the last 150 years. We also know the forcing of greenhouse gases.

But since we don't know how much aerosols cool the atmosphere, we don't know the total forcing. So we can't accurately calculate earth's climate sensitivity.

Aerosols offset the effect of greenhouse gases, making the earth appear less sensitive to forcing than it really is.

If we eliminate aerosols, the earth's temperature will react more quickly to changes in greenhouse gas forcing.

If aerosol forcing has been small, then the Earth's true sensitivity will not be so different from what we have observed. Eliminating aerosols will lead to a relatively small increase in temperature.

On the other hand, if aerosol forcing has been strong... well, see for yourself...

temperature in 1850
current temperature
greenhouse gas

Here's our explainer video on aerosols and their effect on climate. Aerosols and the Climate.