Imagine for a minute that global warming isn't anthropogenic-- that it is happening, but it is happening because of... oh, I dunno, sunspots or an overabundance of squirrels or some other natural cause.
Would we just resign ourselves to dealing with the consequences, or would we try to do something about it?
Would environmentalists be lobbying for geoengineering solutions to save polar bear habitat or would they be protesting proposed geoengineering, waving signs saying "Don't Fool With Mother Nature!"
I bet they'd be waving signs.
If the consequences are the same, why does the cause matter? Would the argument be "we didn't cause the problem, so we don't have to fix it?" Or would it be the Appeal to Nature fallacy ("if it is natural, it must be good; if unnatural, bad")?
There are lots of problems we don't cause that we try hard to fix or prevent (diseases, natural disasters), so I don't think that would be the argument. I think instead there would be a double Appeal to Nature-- if global warming was natural, then it must be good. And geoengineering is unnatural, so it must be bad. So, the argument would go, we should do nothing.
I don't believe in the Appeal to Nature, and I don't think it matters whether or not global warming is "natural" or man-made. I think we should weigh the costs and benefits of global warming and compare them to the costs and benefits of possible solutions to figure out what, if anything, we should do.
And I expect that'll happen when Whole Foods decides to get rid of its Natural and Homeopathic Remedies aisle. I predict we'll have genetically engineered flying pigs before then (on second thought, that's dumb; they'll create chickens that taste like bacon).