Geoengineering techniques may fail to undo climate change

Researchers have showed that reducing the amount of sunlight reaching the planet's surface by geoengineering may not undo climate change after all.

Axel Kleidon and Maik Renner of the Max Planck Institute for Biogeochemistry in Jena, Germany, used a simple energy balance model to determine how sensitive the water cycle is to an increase in surface temperature due to a stronger greenhouse effect and to an increase in solar radiation.

They predicted the response of the water cycle for the two cases and found that, in the former, evaporation increases by 2 per cent per degree of warming while in the latter this number reaches 3 per cent.

A stronger greenhouse effect puts a thicker 'lid' over the Earth's surface but, if there is no additional sunlight (if we don't turn up the heat on the stove), extra evaporation takes place solely due to the increase in temperature.

Turning up the heat by increasing solar radiation, on the other hand, enhances the energy flow through the Earth's surface because of the need to balance the greater energy input with stronger cooling fluxes from the surface.

As a result, there is more evaporation and a stronger effect on the water cycle.

In the new Earth System Dynamics study the authors also show how these findings can have profound consequences for geoengineering.

Many geoengineering approaches aim to reduce global warming by reducing the amount of sunlight reaching the Earth's surface (or, in the pot analogy, reduce the heat from the stove).

But when Kleidon and Renner applied their results to such a geoengineering scenario, they found out that simultaneous changes in the water cycle and the atmosphere cannot be compensated for at the same time. Therefore, reflecting sunlight by geoengineering is unlikely to restore the planet's original climate.

The results have been published in the European Geosciences Union (EGU).