Injecting particulates into the atmosphere isn’t a magical fix for the climate crisis | Mike Hulme
P.Solar geoengineering interventions on a global scale involve the deliberate injection of natural or artificial particles into the stratosphere – stratospheric aerosol injection, or SAI – to offset some of the global warming caused by greenhouse gases. If implemented, the technology would create a metaphorical thermostat for the planet. Such a thermostat is advocated on the grounds that controlling global temperature reduces the damage associated with the climate crisis.
I would like to challenge this assertion.
Global temperature was first adopted at the start of this century as a way to index the extent of human impact on the climate system. Since then, global temperature management has become the main focus of climate policy, with the stated objective of the Paris Agreement being to contain global warming between 1.5°C and 2°C. The policy goal of net zero emissions stems from this target temperature range.
SAI seeks to remove a few hundredths, or even two or three tenths of a degree Celsius, from this temperature index. To do this, it is not a question of eliminating the cause of unwanted warming – the accumulation of greenhouse gases in the atmosphere – but of deliberately adding new elements, active particles, to the atmosphere. On a global average, this could slow the build-up of heat in the climate system; this could indeed significantly lower global temperatures.
In my opinion, there are many problems with this technological solution to the climate crisis. But here I want to draw attention to just two: It does little to defuse most of the risks that actually matter to people and ecosystems, and, worse than that, it risks making some of those damages, perhaps even many of them, worse. Both concern the difference between global temperature and the daily weather conditions experienced by people and places.
First, global temperature is only the most rudimentary proxy for the diverse, multi-scale harms associated with greenhouse gas loading in the atmosphere. Many factors include the disruption and reconfiguration of regional weather systems, the impacts of evolving extreme weather events on vulnerable local communities and ecosystems, and the consequences of increasing acidification of the planet’s oceans. Reducing the global temperature by lowering it through solar geoengineering offers no guarantee that these damages will be reduced.
Second, the artificial addition of new radiatively active particles to the atmosphere will inevitably alter the dynamics of global atmospheric circulation that determine regional and local climate. This is clear whether one draws evidence from the analog case of explosive volcanic eruptions or from the results of SAI climate model simulations. The path of hurricanes, the strength of the Indian monsoon, the behavior of El Niño in the Pacific Ocean – in other words, everyone’s weather – then become things for which deliberate solar engineers must take responsibility.
Climate policy should focus on interventions – whether technological, regulatory or behavioral – that directly address the causes of climate damage. This requires focusing on reducing greenhouse gas emissions, implementing ways to remove them from the atmosphere, building the resilience of human and ecological systems to a wide range of climate risks, and investing in the drivers of human development, which have long been shown to be cost-effective in reducing damage, morbidity, and mortality from hazardous weather.
Adopting the global temperature index as a scientific object to be monitored by SAI may seem like it is doing good, but it is an illusion. Pursuing ISC as a desirable and cost-effective way to reduce the main damages of the climate crisis is an unnecessary and risky distraction from what matters most: reducing human emissions into the atmosphere, not adding new man-made materials.
