23rd February 2014
Abrupt end to geoengineering could spell disaster
Injecting sulfate particles into the atmosphere to reflect sunlight and cool the Earth is one potential solution to global warming. If this process was ended too suddenly, however, the results would be catastrophic, based on research by the University of Washington.
Carrying out geoengineering for several decades and then stopping would trigger warming at a rate far exceeding that expected due to global warming, according to a study published this week in Environmental Research Letters.
"The absolute temperature ends up being roughly the same as it would have been – but the rate of change is so drastic, that ecosystems and organisms would have very little time to adapt to the changes," said lead author Kelly McCusker.
The study looks at solar radiation management, a proposed method of geoengineering by spraying sulfur-based particles into the upper atmosphere to reflect sunlight. This is similar to what happens after a major volcanic eruption, and many experts believe the technique is economically and technically feasible. But continuous implementation over decades will depend on technical functioning, continuous funding, international agreement and lack of negative side effects.
The team used a global climate model to simulate a business-as-usual emissions trend until 2035, when geoengineering would be implemented for 25 years – then suddenly stopped at 2060. The model showed that global temperatures could jump by 4°C in the following three decades (shown by the yellow lines in the graphs below), a rate more than double what it would have been otherwise, and far exceeding historical temperature trends.
These results build on recent work led by UK researchers pointing to the risk of implementing and then abruptly stopping geoengineering. That study compared several climate models, showing that the result is not specific to any one model. This new study used a single model with a more realistic scenario, where instead of simply decreasing the Sun's strength, they actually simulated sulfate particles to stabilise the temperature (shown in blue), allowing a more precise look at the geographic and seasonal patterns.
"The changes that will be needed to adapt to a warmer climate are really profound," said co-author David Battisti, professor of atmospheric sciences. "The faster the climate changes, the less time farmers have to develop new agricultural practices, and the less time plants and animals have to move or evolve."
The total amount of warming after stopping geoengineering would be largest in winter near the poles – but compared to typical historical rates of change, the most extreme effects would be seen at the tropics during summertime, where there is usually very little temperature variation.
“According to our simulations, tropical regions like South Asia and sub-Saharan Africa would be hit particularly hard, the very same regions that are home to many of the world’s most food-insecure populations,” McCusker said. “The potential temperature changes also pose a severe threat to biodiversity.”
The researchers looked at different variables and found that the rate of warming is largely determined by the length of time that geoengineering is deployed and the amount of greenhouse gases emitted during that time, rather than by how sensitive the climate is to changes in greenhouse-gas concentrations.
“If we must geoengineer, it does not give us an excuse to keep emitting greenhouse gases,” she added. “On the contrary – our results demonstrate that if geoengineering is ever deployed, it’s imperative that greenhouse gases be reduced at the same time to reduce the risk of rapid warming.”
Even a dramatic reduction in carbon emissions may prove insufficient, however. The momentum already locked into the climate system will drive warming for centuries to come, according to a recent study published in Nature. The evidence seems to be accumulating that we need to actually reverse CO2 levels – not just slow emissions – likely through a range of additional measures such as carbon capture and storage.