Chapter

Paris Climate Agreement: Beacon of Hope

Part of the series Springer Climate pp 51-113

Open Access This content is freely available online to anyone, anywhere at any time.

Date:

Forecasting Global Warming

  • Austin P. HopeAffiliated withDepartment of Atmospheric and Oceanic Science, University of Maryland
  • , Timothy P. CantyAffiliated withDepartment of Atmospheric and Oceanic Science, University of Maryland
  • , Ross J. SalawitchAffiliated withDepartment of Atmospheric and Oceanic Science, University of MarylandDepartment of Chemistry and Biochemistry, University of MarylandEarth System Science Interdisciplinary Center, University of Maryland
  • , Walter R. TribettAffiliated withDepartment of Atmospheric and Oceanic Science, University of Maryland
  • , Brian F. BennettAffiliated withDepartment of Atmospheric and Oceanic Science, University of Maryland

Abstract

This chapter provides an overview of the factors that will govern the rise in global mean surface temperature (GMST) over the rest of this century. We evaluate GMST using two approaches: analysis of archived output from atmospheric, oceanic general circulation models (GCMs) and calculations conducted using a computational framework developed by our group, termed the Empirical Model of Global Climate (EM-GC). Comparison of the observed rise in GMST over the past 32 years with GCM output reveals these models tend to warm too quickly, on average by about a factor of two. Most GCMs likely represent climate feedback in a manner that amplifies the radiative forcing of climate due to greenhouse gases (GHGs) too strongly. The GCM-based forecast of GMST over the rest of the century predicts neither the target (1.5 °C) nor upper limit (2.0 °C warming) of the Paris Climate Agreement will be achieved if GHGs follow the trajectories of either the Representative Concentration Pathway (RCP) 4.5 or 8.5 scenarios. Conversely, forecasts of GMST conducted in the EM-GC framework indicate that if GHGs follow the RCP 4.5 trajectory, there is a reasonably good probability (~75 %) the Paris target of 1.5 °C warming will be achieved, and an excellent probability (>95 %) global warming will remain below 2.0 °C. Uncertainty in the EM-GC forecast of GMST is primarily caused by the ability to simulate past climate for various combinations of parameters that represent climate feedback and radiative forcing due to aerosols, which provide disparate projections of future warming.

Keywords

Global warming projections Attributable Anthropogenic Warming Global warming hiatus Climate feedback