"The mitigating steps we took were too slow and too small. Countries did come together to sign the UN Framework Convention on Climate Change at the Earth Summit in Rio de Janeiro in 1992. The aim of the treaty was to reduce greenhouse gas emissions back to 1990 levels by the year 2000. However, the agreement was toothless because its emissions reduction obligations were unenforceable. The participation of the US was important and a cause for hope, given that it had thus far contributed the most to global carbon dioxide emissions. The US Congress ratified the agreement and Bill Clinton's election to the presidency that same year seemed to bode well for climate action. But when the new president tried to implement an energy tax as a first mandatory measure to restrain emissions, he encountered strong opposition in Congress and withdrew his proposal. Taxes are the 'third rail' of US politics and, to this day, carbon taxes face a difficult path to adoption."