"GLOBAL ISSUES, LEADERSHIP CHOICES":

It is not clear that concerns about climate change have gotten to the point that governments are seriously considering geoengineering -- who would make the decision to use it? -- but the science has been advancing. This article provides a quick summary of one kind of potential geoengineering: seeding the upper atmosphere with sulfur.

"Changing our behaviour towards the environment is increasingly being seen as a necessity, but making large-scale alterations to our lifestyles is taking time. ... While a solid, long-term fix is being developed, potentially radical methods are increasingly being considered. Solar geoengineering (SG) requires using fleets of aircraft to inject tonnes of sulphur into the stratosphere – between six and 30 miles into the sky. Despite sounding unorthodox, it’s a technique that has been on the minds of climate scientists for a while. A team of researchers from Harvard University, Princeton University, and the Massachusetts Institute of Technology (MIT) has started to take the initiative and have published their findings in Nature Climate Change. ... The thinking is that by injecting sulphur into the atmosphere, it will form a reflective layer, dimming the sun’s rays and cooling the planet’s temperature. This belief isn’t entirely abstract. In 1991, following the eruption of Mount Pinatubo in the Philippines, 17 megatons of sulphur dioxide entered the stratosphere. This cooled the Earth’s average temperature by 0.5°C. ... Approximately two years after the Pinatubo eruption, the effects wore off. ...

"Dimming the sun’s rays has been shown to impact plant life, plants that currently offset some 25 per cent of humanity’s CO2. It would also put food supplies under strain. Further, as solar geoengineering doesn’t negate CO2 emissions, the process of oceanic acidification continues. The oceans absorb one-third of our CO2, which raises its acidity levels. Over the last 200 years, the acidity of the oceans has increased by 26 per cent. This leads to the breakdown of calcium carbonate, which destroys corals and damages shell-based life. Also endangered by oceanic acidification are the water-based, microscopic organisms known as phytoplankton. Although tiny in size, these organisms account for half of the amount of oxygen we breathe. They also produce the chemical dimethylsulphide, a crucial part of the nuclei of water vapour, allowing it to form into raindrops. With less phytoplankton there would be less dimethylsulphide, which means less rain and more drought."
geographical.co.uk/nature/climate/item/3296-sun-block