Greenhouse Gasses
Greenhouse gases such as CO2 (carbon dioxide) and CH4 (methane) will become more noticed in the future, and the populace will pressure the politicians of each nation to endorse greenhouse-gas-emission-reduction plans such as the Kyoto Protocols. Once that is accomplished, and hand-in-hand with plans for placing atmospheric carbon dioxide into carbon sinks (see Iron Seeding), the amount of greenhouse gases in the future will noticeably decline.