Our planet is on the brink. The recently released IPCC Summary for Policymakers warns of the dangers of the already changing climate — warmer oceans, melting snow and ice, and increased sea levels. It provides a clear signal that there is no more time to waste when it comes to tackling the most serious challenge facing humanity today. Swift, effective and large reductions in greenhouse gases must start now. At the 19th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP19), countries have the opportunity and the obligation to prove that they are serious about reining in climate change. One quick and relatively straightforward initiative they can take is to support action under the Montreal Protocol to phase down the fastest growing source of man-made greenhouse gas emissions, the family of chemicals known as hydrofluorocarbons (HFCs).