We know of one technique that temporarily but significantly cools the globe—a massive volcanic eruption—and I wonder how bad the climate crisis has to get before that option is seriously mooted. Or how a serendipitous eruption would affect the politics of this issue. 
If we had the technology, a controlled popping of Rainier, Baker, Adams, or St. Helen's could be an important safety measure. Let the pressure out and release the lahars in a safe direction.