The big picture: Efforts to reduce global greenhouse gas emissions aren't working, and the world is on track to exceed the 1.5° C limit set with the Paris Agreements goal. As such, emergency "temporary" measures like Solar Radiation Modification should be considered to buy humanity more time to avoid the worst.
Solar Radiation Modification (SRM), or more broadly solar geoengineering, is a type of technologies that can theoretically reflect sunlight back into outer space thus cooling Earth's atmosphere. According to a newly-published report by the United Nations, SRM is still a "speculative group of technologies" which should, however, be studied more rigorously as we are running out of time for any meaningful effort to curb global warming.
Prepared by a panel of experts within the United Nations Environment Programme (UNEP), the report is promoting a rapid review of the state of scientific research on SRM technology and solutions. Climate action is lagging, the experts say, but solar geoengineering still requires more research before any consideration for "potential deployment."
SRM could knock the global average temperature down in a very short timeframe, but it also brings some dangerous risks for the future of our planet. After all, we only have one atmosphere, the experts warn, so we can't risk a global catastrophe because we are in a hurry to bring down the temperatures of an increasingly hotter, inhospitable and unpredictable planet.
Speculations about the potential effects of reflecting solar radiation back into space are based on the observations of aerosol particles spreads by large volcanic eruptions into the upper atmosphere. Scientists know that a "deliberate injection of large amounts of reflective particles into the stratosphere would cool the Earth rapidly," the UN report says.
If global warming were to produce intolerable outcomes such as widespread famines, mass migration, mass mortality or infrastructure destruction, the report states, a "planned" emergency response based on SRM technologies could alleviate some of the harsher effects of a worsening global warming within a few years.
But SRM can be extremely dangerous and bring many ethical issues to the table, as it's a relatively low-cost solution - with an estimated $20 billion expense per 1 degree Celsius of cooling per year - within reach of many countries and potentially "rogue" organizations.
For instance, sulfur dioxide is one of the substances commonly proposed as an aerosol, but it could result in acid rain and deplete the recently recovered ozone layer over the Antarctic. Furthermore, acid rain would also affect those countries which didn't agree to the SRM option, so a discussion within the United Nations is the only viable way to bring global consensus on the matter.