Atmospheric pressure.

The article focuses on the success and failure of various environmental protocols. In Montreal, the threat came mainly from the harm that chlorofluorocarbons do to the ozone layer; in Kyoto, from gases such as carbon dioxide that many scientists say are changing the climate. Both treaties thus tried to tackle problems that potentially affect every country, and are caused by activities that occur in every country. Both were negotiated against a background of scientific uncertainty. The science of ozone depletion was uncertain when the Montreal Protocol was negotiated in 1987; the uncertainties surrounding the science of climate change are huge.