A new study has warned of risks posed by unregulated geoengineering techniques designed to lower high temperatures in specific areas. These efforts may only provide temporary benefits for some populations while introducing negative impacts for other parts of the world.
In order to meet the goals set by the 2015 Paris Climate Agreement, countries around the world will need to embrace various approaches. This will likely include a mixture of greenhouse gas emissions reduction techniques, and carbon dioxide removal, as well as what is called solar geoengineering.
This latter approach involves deliberately cooling the planet by reflecting more sunlight back into space. For instance, a technique known as marine cloud brightening increases reflectivity of certain clouds so that they can bounce sunlight back into space. The hope among its advocates is that this will help offset some impacts of climate change.
One way to achieve this is by seeding naturally occurring sea salt into clouds, which is also amenable to regional applications since it can be deployed in the lower troposphere over a localized area. And this is where the challenge comes in.
According to a new study, targeted interventions in one place may have unforeseen consequences for other parts of the world. This situation is made worse because there are currently few, if any, regulations to oversee and scrutinize regional applications of specific techniques.
As climate change becomes more disruptive, it is possible more countries will seek local options – like marine cloud brightening – to help their own populations, especially as global schemes are often fraught with challenges. But because there are few relevant regulations, it is possible cities, companies, or even wealthy individuals could try to modify their local climates.
The rise in heatwaves across the world has led some research institutions and private companies to investigate geoengineering options. For instance, over the last four years, Australia has been trialing marine cloud brightening techniques that may help cool the Great Barrier Reef, thereby slowing coral bleaching.
According to the new study, the effect of cloud brightening techniques may well diminish or even reverse as climate conditions continue to shift due to human causes, such as the continued use of fossil fuels.
As the authors say, “the effects of regional schemes – which have been little researched so far – may prove much more difficult to predict than global ones because concentrated, rather than diffuse, forcings are more likely to trigger nonlinear climate responses.”
The team used Earth system computer models of the climate in 2010 and 2050 and compared simulations of two cloud brightening initiatives. The initiatives, which were carried out to reduce the impacts of severe heat, took place in different regions of the northeastern Pacific Ocean, one near California and one near Alaska.
The simulation for 2010 indicated that cloud brightening near Alaska, a mid-latitude area, would lower the risk of dangerous summer heat exposure by 55 percent, while the scheme near California, a subtropical area, would result in a more modest 16 percent reduction.
However, the simulations for 2050, which take into account the turbulent conditions introduced by ongoing climate change, produced far more worrying results. Because there were fewer clouds, as well as a higher base temperature and the gradual slowing of the Atlantic Meridional Overturning Circulation (AMOC), the initiative in Alaska did not have the same impact as it did in the 2010 simulation, while the initiative for California actually raised temperatures, achieving the opposite result.
At the same time, the mid-century simulations showed that local attempts to cool the climate increased temperatures and stresses across the world, especially in Europe. This was because of the slowing of the AMOC.
In effect, cloud brightening may have some local benefits now, but as time goes on the impacts will become less predictable and much more damaging for other places.
“Unintended side effects of [solar engineering] remain one of the strongest concerns about any future deployment, regional or otherwise,” the researchers explain.
“An examination of the complex mechanisms that make this remote intervention effective at regional cooling under present-day conditions, but ineffective under warmer mid-century conditions, illustrates the challenges scientists and decision makers will face if climate risk management proposals such as [marine cloud brightening] remain largely ungoverned, as they are today.”
The current research may underestimate the extent to which future cloud brightening interventions could cause unexpected responses as the background climate state continues to change. What may appear promising at a regional level could well result in drastic issues elsewhere if they cannot be regulated or managed properly.
The study is published in Nature Climate Change.
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