Climate change risk could be mitigated with the right dose of geoengineering

Geoengineering is the deliberate manipulation of the climate, mainly to reduce the impact of climate change, and encompasses the capture of huge amounts of carbon dioxide from the atmosphere through tree planting, artificial carbon storage, or blasting aerosols into the atmosphere to create a ‘global dimming’ effect.

Previous studies have warned that the latter approach may only be beneficial for certain regions of the planet, while other areas could face devastation.

But now UCL and Harvard researchers suggest that even a crude method, like injecting sulphur dioxide in the stratosphere, could reduce many important climate hazards without making any region obviously worse off.

Previous research shows that solar geoengineering could be achieved using commercially available aircraft technologies to deliver the particles at a cost of a few billion dollars per year and would reduce global average temperatures.

The researchers took data from a sophisticated simulation of stratospheric aerosol geoengineering to evaluate whether the approach could offset or worsen the effects of climate change around the world. How these effects differed under different temperature scenarios was also tested.

The team found that halving warming by adding aerosols to the stratosphere could moderate important climate hazards in almost all regions. They saw an exacerbation of the effects of climate change in only a very small fraction of land areas.

Lead author, professor Peter Irvine (UCL Earth Sciences), said: “Most studies focus on a scenario where solar geoengineering offsets all future warming. While this reduces overall climate change substantially, we show that in these simulations it goes too far in some respects leading to about 9 per cent of the land area experiencing greater climate change, i.e. seeing the effects of climate change exacerbated.

“However, if instead only half the warming is offset, then we find that stratospheric aerosol geoengineering could still reduce climate change overall but would only exacerbate change over 1.3 per cent of the land area.”

The team emphasise that solar geoengineering only treats the symptoms of climate change and not the underlying cause, which is the build-up of CO2 and other greenhouse gases in the atmosphere. It should therefore be considered as a complementary approach to emissions cuts as a way to address climate change.

“Our results suggest that when used at the right dose and alongside reductions in greenhouse gas emissions, stratospheric aerosol geoengineering could be useful for managing the impacts of climate change. However, there are still many uncertainties about the potential effects of stratospheric aerosol geoengineering and more research is needed to know if this idea is truly viable,” Irvine added.

The team used data from the Geoengineering Large Ensemble Study, which used a sophisticated climate-chemistry model to simulate the climate response to a hypothetical deployment of stratospheric aerosol geoengineering.

In this model study, sulphur dioxide was released at different latitudes in the Tropics to produce a layer of aerosols tuned to keep temperatures steady under an extreme global-warming scenario.

Co-author professor David Keith said: “Early research with climate models consistently shows that spatially uniform solar radiation modification could significantly reduce climate risks when combined with emissions cuts. But, should we trust the models? Uncertainties are deep and no single result is trustworthy, but this paper is a step towards more realistic modelling from injection to regional impacts.”

The team are now researching the projected effects of stratospheric aerosol geoengineering on the water cycle in more depth to try to understand the potential benefits and risks to society and ecosystems.