I mostly like Andrew Dressler's obesity-climate change analogy. To summarize: a. responding to obesity by cutting calories is like responding to climate change by reducing emissions; b. responding to obesity by not fighting it and simply adapting to the increased weight and health problems is like adapting to climate change through seawalls etc.; and c. responding to obesity by getting gastric-bypass or similar surgery is like geo-engineering in terms of riskiness.
While the analogy is slightly unfair in the case of adaptation, I think it's easy for the lay person to understand. The best part is the analogy between gastric-bypass surgery and geo-engineering in pointing out the extreme nature and risk involved in geo-engineering.
The analogy's value that Dressler might not have intended is that in some scenarios, surgery to treat obesity is a good idea despite the risks. If the patient is sufficiently, morbidly obese and otherwise unable to lose weight, the several-percent mortality risk from surgery and infection is less dangerous than forgoing surgery. The same may be true of geo-engineering - we're not in that situation yet, but we may end up in a situation where the political will exists for a risky geo-engineering solution but not for sufficient emissions reduction. I just hope it doesn't come to that.
And while we're on the analogy subject, I still like my analogy between managing groundwater and managing greenhouse gas emissions. The obesity metaphor is far more accessible to most people, but I think groundwater policy challenges are very similar to climate issues. While the 150 years of mistakes and mismanagement of groundwater in the US is hardly encouraging, it does provide some lessons (and we're even getting better at it, in some places).