The Impact of Public Perception of Timescales in the Climate System on Mitigation Policies

Note: The purpose of this contribution is to initiate awareness of well-known long-term consequences of climate mitigation measures, and as such it is a debating essay rather than a scientific publication. The consequences of climate change are often communicated with reference to a 100-year timescale, even though the timescales of different climate forcing mechanisms vary with several orders of magnitude. In the Intergovernmental Panel on Climate Change (IPCC) assessment reports, a 20-, 100-, and 500-year global warming potential metric has been used to quantify the impact of climate forcers. The United Nations Climate Conferences have adopted the 100-year global warming potential (GWP100y) metrics, and this measure has become the common reference and has as such come to stand alone in the public and political discussions. We demonstrate that the 100-year metric can be misleading and directly harmful to the environment on longer timescales (500–1000 years), when used as reference for political decisions. The basic mechanism being emphasized here is that the 100-year metric weights relatively short-lived anthropogenic climate forcers, such as, for instance, methane and nitrous oxide, unreasonably high in the emission budget. This is especially the case if a fixed emission reduction target has been set prior political negotiations about mitigation policies.