The dozens of ways that scientists, as well as crackpots, have proposed to geoengineer the world's climate won't all be equally effective. In fact, some of them, particularly the ones that rely on sucking up carbon dioxide instead of blocking out solar radiation, will hardly have any impact at all, a new study in the journal Atmospheric Chemistry and Physics found.

"By 2050, only stratospheric aerosol injections or sunshades in space have the potential to cool the climate back toward its pre-industrial state," earth scientists Tim Lenton and Naomi Vaughan of East Anglia University in England write.