Geoengineering options reviewed
Experts have reflected on ideas to combat climate change through ‘geoengineering’.
Scientists are exploring options in addition to carbon reduction to mitigate the warming of the planet, in particular geoengineering methods that alter the radiative balance of the planet, thereby reducing warming.
Researchers Ulrike Niemeier and Simone Tilmes have gone over the pros and cons of continuously injecting sulfur into the stratosphere — a technique called stratospheric aerosol modification (SAM).
Models suggest that SAM would mitigate greenhouse gas-induced changes in global temperatures and extreme precipitation.
However, anticipated side effects include slowing of the hydrological cycle, which would affect water availability and reduce monsoon precipitation.
The experts caution that the extent of injection required for a given level of cooling is uncertain, varying widely between models.
Understanding the economic costs and technological requirements of SAM is also critical, they say.
Assuming a scenario in which aggressive mitigation and large-scale carbon capture and removal start as late as 2040, sulfur would need to be injected for 160 years to limit the temperature increase to 2°C above preindustrial levels – such endeavours could cost US$20 billion a year.
Additionally, Ulrike Lohmann and Blaž Gasparini have looked at ways to manipulate clouds so that they absorb less of the outgoing longwave radiation from Earth’s surface.
Wispy, thin cirrus clouds, at high altitudes, can absorb longwave radiation, creating a heating effect. Scientists are using models to explore ways in which to make artificial, low-altitude cirrus clouds that trap less heat. The artificial clouds are made using molecules that attract moisture.
The authors note a number of caveats with widespread use of this approach, citing a potential reduction in global mean precipitation and intensification of tropical convection. If artificial creation of cirrus clouds is not done carefully, the effect could be additional warming rather than the intended cooling, they say.