Geoengineering

contact: Ulrike Niemeier, Hauke Schmidt

What is Geoengineering?

"Geoengineering" or "climate engineering" may be defined as the deliberate large-scale manipulation of climate. The study of such techniques has been proposed in order to prepare for the cases that attempts to limit projected climate change by the reduction of greenhouse gas concentrations may fail or that consequences of climate change may prove worse than expected.

In general, two main classes of geoengineering techniques are distinguished:  

1) Carbon dioxide removal techniques (CDR) would address the root cause of climate change by removing greenhouse gases from the atmosphere. Proposed techniques are, e.g.:

• Technical capture of carbon from the atmosphere

• Ocean fertilization to enhance uptake by biological systems

2) Solar Radiation Management techniques (SRM) would attempt to offset effects of increased greenhouse gas concentrations by reducing the amount of sunlight absorbed by the earth. Proposed techniques are, e.g.:

• Increasing the surface reflectivity of the planet by brightening human structures (e.g. by painting them white), planting of crops with a high reflectivity, or covering deserts with reflective material;
• Enhancement of marine cloud reflectivity;
• Shields or deflectors in space to reduce the amount of solar energy reaching the Earth;
• Injections of sulfate aerosols into the lower stratosphere to mimic the effects of volcanic eruptions.

Why do we study geoengineering?

The topic of geoengineering is highly controversial. Sometimes it is argued that already the discussion of this technique may have deleterious effects because it may distract or prevent people from studying and investing in options to reduce the emission of greenhouse gases, while they are expecting a geoengineering solution to the climate problem. However, at a certain point in time, when effects of climate change may become more evident than today, geoengineering techniques will likely be considered seriously. We think that that the expected debate on geoengineering should be prepared by independent research activities. This is in particular true as the effectiveness of most geoengineering techniques is unclear, and they may have undesirable side effects for crucial parts of the Earth system and humankind.

How do we study geoengineering?

The goal of our research is to better understand efficiency, risks and side-effects of proposed SRM techniques. To this end we are using numerical climate models which we see as an essential tool estimate the possible impact of geoengineering. Earlier climate model simulations of solar radiation management techniques have led to partly inconclusive results. It is unclear tho what extent this may be due to differences in the model formulations or in the simulated scenarios. To overcome this situation we have proposed the IMPLICC project. In this EU FP7 project, several European groups perform a coordinated set of numerical experiments with different models. At the same time, the GeoMIP initiative has proposed a similar approach on a larger scale, including groups from many parts of the wold. These sets of coordinated experiments should help to identify which of the simulated climate responses to geoengineering are a robust feature of many models.