The Climate Impacts of Hydrofluorocarbons (HFCs): From the Earth's Surface to the Middle Atmosphere

Hydrofluorocarbons (HFCs) are second-generation replacements for the chlorofluorocarbons (CFCs), halons and other substances that caused the ‘ozone hole’. While HFCs do not contain the chlorine or bromine atoms necessary to directly deplete ozone, they are strong greenhouse gases with rapidly increasing atmospheric concentrations, and so could significantly modify the radiative and dynamical balance of the future atmosphere. This study presents simulations that identify the potential climate impacts of HFCs.

Previously, NASA GSFC 2D model simulations showed that HFCs modulate the climate of the upper troposphere and stratosphere: HFCs increase atmospheric temperature and enhance the overturning circulation, thus affecting stratospheric ozone concentrations. Under a business-as-usual emissions scenario, HFCs could contribute substantially to anthropogenic middle atmospheric change by the mid-21^st century.

Recent estimates suggest that the radiative forcing by HFCs could be as large as 20% that of CO₂ by the mid-21^st century. A CFC-11-based proxy for the HFCs has been shown to warm surface temperatures, similarly to the effects of increasing CO₂. New ocean-atmosphere Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) simulations with interactive HFCs provide the first quantitative estimates of the contribution of HFCs to future climate change. Specifically, these simulations identify the HFC contributions to future changes in surface temperature, precipitation and interannual variability. GEOSCCM sensitivity simulations contrast the climate impacts of HFCs in a business-as-usual emissions scenario with a scenario depicting the evolution of HFC emissions following the Kigali Amendment to the Montreal Protocol.