Limitations of climate engineering

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 (CO₂) 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.

“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-CO₂ 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 CO₂
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.