Actually, some creative thinkers think you can. They have proposed detonating nuclear bombs in remote areas to throw up enough debris into the stratosphere to create a veil that reduces the amount of solar radiation that reaches the earth—in other words, an intentional, mild nuclear winter (or better: a nuclear autumn). Basically, the aim would be to obtain the cooling effect that is already known to be caused by volcanic eruptions, especially those in lower latitudes. (Speaking of which, the 20th century saw fewer volcanic eruptions than the 19th, 17th, and 16th centuries.) This sort of geo-engineering might sound like science fiction, but so do many unconventional ideas when they are first proposed.
Along these lines, many of the people who most fear global warming would greatly benefit from reading “hard” science fiction, which vastly expands one’s sense of the scientifically and technologically possible—for both good and evil. As the great doomslayer Julian Simon never stopped reminding us, the human mind is the ultimate resource. Admittedly, this sense of Promethean possibility must be tempered by what is politically possible; as far as I know, there is still no genre of social-science fiction.