Despite international agreements on climate protection and political declarations of intent, global greenhouse gas emissions have not decreased. On the contrary, they continue to increase. With a growing world population and significant industrialization in emerging markets such as India and China the emission trend reversal necessary to limit global warming seems to be unlikely. Therefore, large-scale methods to artificially slow down global warming are increasingly being discussed. They include proposals to fertilize the oceans, so that stimulated plankton can remove carbon dioxide (CO 2 ) from the atmosphere, or to reduce the Sun's incoming radiation with atmospheric aerosols or mirrors in space, so as to reduce climate warming. All of these approaches can be classified as "climate engineering". "However, the long-term consequences and side effects of these methods have not been adequately studied," says Dr. David Keller from the GEOMAR Helmholtz Centre for Ocean Research Kiel. Together with colleagues the expert in earth system modeling has compared several Climate Engineering methods using a computer model. The results of the study have now been published in the internationally renowned online journal Nature Communications.

!ADVERTISEMENT!

"The problem with previous research was that in most cases the methods were studied with different models using different assumptions and different sets of earth system components, making it difficult to compare the effects and side effects of different methods," Dr. Keller says. He adds: "We wanted to simulate different climate engineering methods using the same basic assumptions and Earth system model". For their study, the researchers chose five well-known climate engineering approaches: The reduction of incoming solar radiation, the afforestation of large desert areas in North Africa and Australia, and three different techniques aimed at increasing ocean carbon uptake. In parallel, the scientists also simulated future changes in the Earth system without climate engineering, based on the high-CO 2 emission scenario used by the UN IPCC.

Even under ideal conditions assumed in the simulations, the potential benefits of the various climate-engineering methods were limited. Only a continuous reduction of solar radiation could prevent the Earth from warming significantly. The afforestation of the Sahara and the Australian outback, however even caused some additional global warming: "The forests removed carbon dioxide from the atmosphere, but at the same time the earth's surface became darker and could store more heat," Dr. Keller explains of this phenomenon. All of the other techniques showed significant side effects, too. For example, the fertilization of the oceans allowed plankton to remove CO 2 from the atmosphere, but also changed the size of ocean oxygen minimum zones.

Read more at GEOMAR Helmholtz Centre for Ocean Research Kiel.

Green engineering image via Shutterstock.