Deploy vast reflective surfaces around the Earth to block some of the sunlight. Extract carbon dioxide from the air and inject it into sediments. Harness plant biomass rich in CO2 to produce electricity… the contributions of climate geoengineering may seem like science fiction. And yet, fundamental research and modelling are already underway.
Geoengineering: a last-resort solution?
On December 12, 2015, after tough negotiations, delegates from the 190 countries that took part in COP21 in Paris reached a draft final agreement to limit global warming to less than 2°C by 2100. This objective, deemed “ambitious”, would nevertheless be insufficient according to a study by the Stanford Woods Institute for the Environment. Indeed, global warming, even if contained, as well as rising sea levels, would increase the likelihood of extreme climate events such as heatwaves, droughts, excessive rainfall and the various weather events that result from them.
“We have determined that humans have already increased the likelihood of historically unprecedented extreme events in 50 to 90% of North America, Europe and East Asia“, the study report states. In short, achieving the Paris Agreement target would limit the damage without eliminating the risk of extreme weather episodes, which would instead tend to become more frequent. Faced with this disaster scenario, the scientific community is mobilising, notably in the field of geoengineering. Some even consider it the last-resort solution in the fight against global warming.
The two main areas of climate geoengineering according to the NAS
According to the Intergovernmental Panel on Climate Change (IPCC), which brings together 195 states under the auspices of the UN, geoengineering refers to “all methods and techniques aimed at deliberately modifying the climate system to combat the effects of climate change“. It is also interesting to note a shift in English-language terminology, suggested by the National Academy of Science (NAS). The term now used is “Climate Intervention“, a more explicit expression to refer to climate-focused geoengineering. The NAS, commissioned by the Obama administration in 2012, suggests two main areas of intervention to support mitigation efforts (reducing CO2 emissions) and adaptation (limiting the impacts of warming on people and the planet).
#1 Decarbonising the atmosphere
The operating method has not yet been finalised, as the fundamental research phase only began in 2018. Of the six avenues previously identified, four were deemed viable. The NAS estimates that the research effort should span two decades, with funding needs between $8.5 and $11 billion:
- New agricultural and forestry practices to capture and store carbon in terrestrial systems (afforestation and reforestation);
- Harnessing plant biomass (containing CO2) to produce electricity and fuels;
- Capturing CO2 from the air and reinjecting it into a geological formation;
- Carbon mineralisation through accelerated weathering.
#2 Solar radiation management
The NAS defines this research area as all techniques likely to “increase the fraction of solar radiation reflected by the Earth“. Mentioned for more than a decade, the technique of artificially introducing stratospheric aerosols appears to be favoured by the scientific community. Directly inspired by volcanic eruptions, it involves releasing particles suspended in the air (similar to the sulphur compounds emitted by volcanoes) to reduce solar radiation. For example, the eruption of Mount Pinatubo in June 1991 reduced solar radiation by 10%. It is estimated that the solar radiation directed towards the Earth must decrease by 3% to bring the planet back to its average pre-industrial temperature.
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