There are other approaches if we absolutely must do geoengineering.
And besides that, many of the people pushing for massive decarbonization don't really care so much about the carbon as they do about the financial, social and political power that is tied up in the policy prescriptions they favor.
From MIT's Technology Review, March 18:
The decision follows years of controversy and the departure of one of the program’s key researchers.
Harvard researchers have ceased a long-running effort to conduct a small geoengineering experiment in the stratosphere, following repeated delays and public criticism.
In a university statement released on March 18, Frank Keutsch, the principal investigator on the project, said he is “no longer pursuing the experiment.”
The basic concept behind solar geoengineering is that the world might be able to counteract global warming by spraying tiny particles in the atmosphere that could scatter sunlight.
The plan for the Harvard experiments was to launch a high-altitude balloon, equipped with propellers and sensors, that could release a few kilograms of calcium carbonate, sulfuric acid or other materials high above the planet. It would then turn around and fly through the plume to measure how widely the particles disperse, how much sunlight they reflect and other variables. The aircraft will now be repurposed for stratospheric research unrelated to solar geoengineering, according to the statement.
The vast majority of solar geoengineering research to date has been carried out in labs or computer models. The so-called stratospheric controlled perturbation experiment (SCoPEx) was expected to be the first such scientific effort conducted in the stratosphere. But it proved controversial from the start and, in the end, others may have beaten them across the line of deliberately releasing reflective materials into that layer of the atmosphere. (The stratosphere stretches from approximately 10 to 50 kilometers above the ground.)
Last spring, one of the main scientists on the project, David Keith, relocated to the University of Chicago, where he is leading the Climate Systems Engineering initiative. The new research group will explore various approaches to solar geoengineering, as well as carbon dioxide removal and regional climate interventions, such as efforts to shore up glaciers.
That summer, the research team informed its advisory committee that it had “suspended work” on the experiment. But it stayed in limbo for months. No final decision on the project’s fate had been made as of early October, Harvard professor Daniel Schrag, who serves on the advisory committee of the university’s broader Solar Geoengineering Research Program, told MIT Technology Review at the time.
Proponents of solar geoengineering research argue we should investigate the concept because it may significantly reduce the dangers of climate change. Further research could help scientists better understand the potential benefits, risks and tradeoffs between various approaches.
But critics argue that even studying the possibility of solar geoengineering eases the societal pressure to cut greenhouse gas emissions. They also fear such research could create a slippery slope that increases the odds that nations or rogue actors will one day deploy it, despite the possibility of dangerous side-effects, including decreasing precipitation and agricultural output in some parts of the world....
....MUCH MORE
