Beware malaria risk from efforts to cool the planet

The writer is a science commentator

It seems like a ingenious solution to an intractable problem. The world may be bungling its promise to limit global temperature rise to less than 2C above pre-industrial levels, but could solar geoengineering ride to the rescue? Methods vary but the basic idea is the same: to reflect sunlight away from Earth.

New research cautions that such a radical attempt to cool the planet, often touted as a win for health, may push up the malaria risk in some countries, even if it decreases disease transmission elsewhere. This points to a painful possibility: what seems like a magic global fix can have a dangerously uneven impact around the world — and may magnify health hazards in countries least able to cope.

Researchers from the US, South Africa, Bangladesh and Germany, led by biologist Colin Carlson at Georgetown University, homed in on a solar geoengineering technique that involves injecting reflective aerosol particles into the stratosphere. The untested method aims to emulate the cooling effect of volcanic eruptions.

The researchers modelled how the resulting cooling could affect the spread of malaria in Africa, Asia and Latin America under moderate and extreme climate warming scenarios. The mosquito-borne disease is the sixth biggest cause of death in low-income countries, with 241mn cases and around 627,000 deaths in 2020, and a brake on economic growth. Furthermore, the two parasites primarily responsible — plasmodium falciparum and, more rarely, plasmodium vivax — are spread by mosquitoes that transmit optimally at around 25C.

The team found that, while artificially cooling the planet is likely to cut malaria transmission in the Indian subcontinent and the Sahel, it could increase transmission in tropical regions such as the Amazon basin, Indonesia, west and central Africa and the south-east and Atlantic coasts of Africa. Brazil, Ecuador, Peru, Venezuela and Mozambique, currently projected to become too hot to sustain spread under some warming scenarios, could cool sufficiently with solar geoengineering to become malarial hot zones.

Under some conditions, by 2070 1bn people spared malarial risk because of global warming would see that risk returned by solar geoengineering. “Without specific research”, the authors wrote in Nature Communications, acknowledging the uncertainty around their findings, “assumptions that solar geoengineering’s health impacts would be intrinsically fair and effective are unsupported, even compared to the most extreme scenarios for climate change.” The conversation about how climate change might alter the pattern of infectious diseases, they add, is dominated by high-income countries that fear the encroachment of new diseases despite having stronger healthcare systems.

Olaf Corry, professor of global security challenges at Leeds University, who was not involved in this study, said it showed solar geoengineering needed to be judged not just on its cooling effect but on wider criteria. And, as well as creating a planetary chill, the work could send a shiver through international relations.

“The geopolitical implications of such uneven effects and risks — or even just the perceived risks of unevenness and unintended consequences — could put up a huge barrier to this technology being used consensually and peacefully,” Corry said. “The controversies around expertise-led interventions for public health are already second to none after the pandemic. Here, you would have a heady mix of global health intervention, climate controversy and the potential for security concerns over leverage — who controls the climate?” What if Russia controlled geoengineering projects to cut methane emission from Siberian tundra, or to stop Arctic sea ice from melting? Few would feel comfortable with Vladimir Putin’s finger on the global thermostat.

The paper urges, broadly, a twin focus on clarity and disparity. First, we need clear thinking on how warming — and any attempt to solve it — affects human health. It is easy to focus on obvious impacts, such as heatwave-related deaths, but harder to track potential complex shifts in infectious disease patterns that might pose a greater overall threat.

Second, different nations face disparate risks — flood, drought, wildfire, deadly heatwaves, crop failure and disease — posed by both climate change and proposed interventions. These are not straightforward to trade off against one another. Working out how that messy patchwork of national interests can be happily stitched into a single climate solution is going to generate its own political heat.