Solar-Radiation Management

Solar-radiation Management Geoengineering with Geographically Varying Strengths

As future climate changes become more severe, people might become interested in ways of offsetting the effects of human-induced climate, which could be cheaper than measures to cut carbon dioxide emissions.

One of the most feasible methods is reducing the amount of solar energy reaching the Earth’s surface by distributing sunlight-reflecting particles high into the atmosphere. This is expected to have a cooling effect on surface temperatures, which would offset the warming effect of high carbon dioxide concentrations.

However, the effects of introducing these particles are not expected to be the same across the globe, and the offsetting of human-induced changes in other quantities such as rainfall and weather patterns may not work as well as for temperature.

High altitudes are desirable for these particles, as the higher parts of the atmosphere are quite self-contained and particles can survive for much longer before being rained out, unlike in the lower and more dense parts of the atmosphere. Unlike other forms of geoengineering (such as direct removal of carbon-dioxide from the air), introducing sunlight-reflecting particles in the high atmosphere is potentially very affordable and practically possible using technologies that already exist today.

It should be noted however that these methods do have potentially undesirable side-effects. Certain particles may have a damaging effect on the ozone layer, vital for keeping harmful UV rays away from the surface of the Earth. Geoengineering methods that don’t remove carbon dioxide from the atmosphere don’t undo the other effects of high atmosphere carbon-dioxide concentrations such as ocean acidification, and our ability to adequately control geoengineering with sunlight-reflecting particles is not certain. All these provide strong reasons for conducting investigations into the effects of this type of geoengineering so we can be as sure as possible of what might happen before any real-world experiments are considered.

One proposed way to carry out this method of geoengineering would have balloon-tethered pipe to pump sulfur aerosols into the stratosphere and block a portion of solar radiation from reaching earth [Read more on the Smithsonian website]
Image Source: Wikimedia Commons, Hugh Hunt.

Solar-radiation Management Modelling Experiment

Most research studies investigating the consequences of introducing these sunlight-reflecting aerosols high in the atmosphere, known as solar radiation management geoengineering (SRM), have investigated the consequences of equal changes in incoming solar radiation across the world using global climate models. However, it is quite conceivable that any actual real-world SRM geoengineering could be conducted with specifically-designed particles such as titania dioxide, which have a short atmospheric residence time, allowing for different amounts of SRM geoengineering to be used in different parts of the world. This geographically-changing SRM geoengineering could conceivably do a better job of more comprehensively compensating for human-induced climate change than with an identical amount at all locations over the globe.

This experiment uses the HadCM3 atmosphere-ocean coupled climate model to test the climate response to SRM geoengineering, localised to specific geographical bands in the north-south direction in the climate model. The uniquely large ensemble of simulations that is achievable with allows us to deduce the changes in the climate due to this regionally-banded SRM geoengineering from the considerable inherent natural fluctuations that occur in local climates.

Assuming that the climate response to multiple regions of banded SRM geoengineering can be shown to be roughly the addition of the individual climate responses, we can use the results of this experiment to identify theoretical limits to the extent that SRM geoengineering could compensate for human-induced climate change, a potentially highly relevant check on the weight trust that politicians should place on cheap geoengineering solutions in climate policy.