I think the best PoD at this point would be for Iraq to fail harder in the Iran-Iraq war and be overrun by Iran. A stronger Iran, not bled white by that conflict, then tries to export Shia Islamism to nearby Shia areas...including the major oil producing regions of Saudi Arabia, Bahrain, Qatar, and the United Arab Emirates. The resulting instability means oil prices remain high through the 1980s instead of falling after 1982. This, in turn, means investors and the United States government are more interested in investing in non-oil energy sources (renewable energy, coal to liquids, fusion, fission, etc.) during the 1980s and 1990s. You could also combine this with instability in other major oil producers to keep prices high; for instance, have Chavez succeed in his 1992 Venezuelan coup d'état, perhaps with damage to the oil infrastructure, have problems in Nigeria, perhaps more problems in Russia, and so on.
Although this doesn't necessarily push climate change per se forwards, it has the side effect of advancing many technologies and investments that have a side effect of alleviating climate change. Combine with something like Gore winning '92 or '88 instead of Clinton or Bush, respectively, or other environmentalists becoming influential political leaders, and you could see some legislation that sort of addresses climate change as part of a broader package of legislation. It would also be very useful if you could get certain right-wing groups to be less hysterically opposed to the idea of doing anything whatsoever to respond to climate change at all, so you could actually negotiations and compromises (eg., in creating a cap-and-trade system, which is after all a Republican idea).
