With a political solution to climate change still appearing distant and unlikely, other solutions, such as reducing the amount of sunlight reaching the Earth's surface, known as geo-engineering, become tempting. However, a team of European researchers warn, the effects of geo-engineering might dramatically alter the world's rainfall patterns. The scientists studied the effects of reducing the amount of sunlight reaching the Earth's surface in a CO2-rich and warm world, resembling one of the Earth's scenarios for 2100.  In this prognosis, desertification might become a serious threat for Europe, North America and the Amazon. Their results are published in Earth System Dynamics, an Open Access journal of the European Geosciences Union (EGU).

Mimicking volcanoes

Geoengineering mimics the effects of mayor volcanic eruptions by sending sulphur dioxide into the atmosphere and releasing enormous mirrors in space, creating an effect called global dimming. Volcanic eruptions, such as the one of the Krakatau volcano (Indonesia) in 1883, release giant amounts of sulphur dioxide to the atmosphere, which has a cooling effect. The same effect on a smaller scale can be seen on a daily basis in the clouds created by commercial airplanes. This is why geo-engineering is being studied as a potential solution to stop global warming. 

The scientists studied four models of climate engineering under a potential future scenario. Hauke Schmidt, lead author of the paper, and his team, state that the study is not intended for future application, but it helps to identify and compare the responses of the Earth's climate to geoengineering and creating a fundament for future research. So what would an engineered climate look like?

In this scenario the CO2 concentration is four times higher than the pre-industrial level, a high estimation but certainly possible at the end of the 21^st century, according to Smith. The heat created from such an increase is balanced by the reduction of radiation from the Sun through geo-engineering.

Major impact on climate 

In the studied scenario rainfall strongly decreases, up to fifteen percent in large areas in northern Eurasia and North America. In the Amazon Basin, the amount of rainfall might even drop by twenty percent. In other tropical regions similar changes can be seen, both positive and negative. In all four models the global rainfall is reduced by five percent.

The implications are still uncertain, but it is clear reducing the amount of solar radiation that reaches the earth's surface will lead to a climate different from any in the Earth's past. Even if the global mean temperature is equal to an earlier age, the global climate is different from any climate before.

This research is the first study to compare the different climate models used in the Fifth IPCC Report and estimate the robustness of their results. In their paper the researchers conclude: "Climate engineering cannot be seen as a substitute for a policy pathway of mitigating climate change through the reduction of greenhouse gas emissions."

The scientists used climate models developed by the UK Met Office's Hadley Centre, the Institut Pierre Simon Laplace in France, and the Max Planck Institute in Germany. Norwegian scientists developed the fourth Earth model used. For direct link to the article by Smith et. al (2012), click here.