To add to this a bit: if increased atmospheric heat is _causing_ the release of greenhouse gases, then directly reducing the temperature of the atmosphere might be the only way to slow down that release. Secondly, since there is a positive feedback loop here, the earlier and more decisively we act to directly reduce the temperature, the less such geoengineering we will need to do. Right now we only need to counteract X parts per million of methane in the atmosphere, but in the future we would need to counteract X+Y parts per million, necessitating a bigger geoengineering response.