Already the accumulation of greenhouse gases in the atmosphere has not only elevated temperatures and increased the frequency of extreme weather events to a disruptive, damaging degree. They have produced a variety of second-order effects which are, in turn, contributing to further warming, and the damage generally. The melting of the polar ice caps means open water where there was ice cover that had previously reflected solar radiation, and the release of methane previously trapped in permafrost, as well as directly raising sea levels. The increased droughts are killing forests that had been great carbon sinks, while the burning trees and rotting wood that result contribute yet more such emissions. And of course, there is the acidification of the carbon dioxide-saturated oceans. The most ambitious decarbonization of our energy and transport system, our industry and food production, is likely to still see positive emissions for decades to come, exacerbating the pattern.
The result is that anything remotely resembling a livable situation requires going beyond zero emissions. The two most obvious courses are negative emissions--the extraction of greenhouse gases from the atmosphere--and the management of solar radiation. Where negative emissions are concerned the most obvious courses are reforestation and afforestation, which can extend to wetlands and undersea kelp "forest" (the latter, offering the nice bonus of directly reversing one of the more worrisome consequences of warming, the acidification of the oceans), and management of the soil. Such natural means can also be supplemented by direct air capture technology, which currently operates on a small scale. Many of these options have the added benefit of generating useful products, with help notable as a potential source of animal feed capable of reducing the methane emissions of cattle-raising, and biofuels; while carbon recovered from the atmosphere can be converted into "buckytubes" with potentially wide applications, from computer chip architectures to large-scale construction and engineering.
Solar radiation management can be carried on through some of the same techniques, with greenery cooling the immediate area, while other techniques entail the reflection of a higher proportion of solar radiation into space. One promising approach is the dispersal of silica across ice to increase its reflection of the sun's rays. More broadly, the conservation and expansion of ice cover is useful in this regard, with the thickening of ice packs through water-spraying one plausible option. Another is the construction of "cooling tunnels" in areas subject to melting, such as Greenland, and the building of sills which prevent warm water from getting underneath them. Additionally melting glaciers and ice shelves can be kept from running off into the sea with the use of walls. (And of course, anything that preserves the ice ameliorates the risk of rising sea levels.)
All this, of course, does not exhaust the full range of options. Others, many more radical (like the fertilization of the ocean with iron, or the use of aerosols to reduce the entry of solar radiation into the atmosphere) also existing. They entail higher risk, but I do not rule them out, especially if the prognosis continues to worsen at the rate it has this past, exceedingly depressing decade. Still, the more modest options discussed above seem to me to offer an ample basis for a comprehensive geoengineering plan, without which any plan to redress climate change cannot be considered anywhere close to complete.
A 100 Percent Renewable Energy-Based Electric Grid?
A 100 Percent Renewable Energy World?
The Mendacity of the Renewable Energy-Bashers
Don't Believe the Trolls; 100 Percent Renewable Energy is Our Best Bet: Postscript
Reflections on the "Moral Equivalent of War"
Don't Believe the Trolls; 100 Percent Renewable Energy is Our Best Bet
My Notes on a Green New Deal
Societal Complexity, Diminishing Returns and a Green New Deal
The Moral Equivalent of War