Articles | Volume 8, issue 3
Earth Syst. Dynam., 8, 617–626, 2017

Special issue: The Earth system at a global warming of 1.5°C and 2.0°C

Earth Syst. Dynam., 8, 617–626, 2017

Short communication 14 Jul 2017

Short communication | 14 Jul 2017

Flexible parameter-sparse global temperature time profiles that stabilise at 1.5 and 2.0  °C

Chris Huntingford1, Hui Yang2,1, Anna Harper3, Peter M. Cox3, Nicola Gedney4, Eleanor J. Burke5, Jason A. Lowe5, Garry Hayman1, William J. Collins6, Stephen M. Smith7, and Edward Comyn-Platt1 Chris Huntingford et al.
  • 1Centre for Ecology and Hydrology, Benson Lane, Wallingford, Oxfordshire, OX10 8BB, UK
  • 2Department of Ecology, School of Urban and Environmental Sciences, Peking University, Beijing, 100871, P.R. China
  • 3College of Engineering and Environmental Science, Laver Building, University of Exeter, North Park Road, Exeter, EX4 4QF, UK
  • 4Met Office Hadley Centre, Joint Centre for Hydrometeorological Research, Maclean Building, Wallingford, OX10 8BB, UK
  • 5Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, UK
  • 6Department of Meteorology, University of Reading, Earley Gate, P.O. Box 243, Reading, RG6 6BB, UK
  • 7Committee on Climate Change, 7 Holbein Place, London, SW1W 8NR, UK

Abstract. The meeting of the United Nations Framework Convention on Climate Change (UNFCCC) in December 2015 committed parties at the convention to hold the rise in global average temperature to well below 2.0 °C above pre-industrial levels. It also committed the parties to pursue efforts to limit warming to 1.5 °C. This leads to two key questions. First, what extent of emissions reduction will achieve either target? Second, what is the benefit of the reduced climate impacts from keeping warming at or below 1.5 °C? To provide answers, climate model simulations need to follow trajectories consistent with these global temperature limits. It is useful to operate models in an inverse mode to make model-specific estimates of greenhouse gas (GHG) concentration pathways consistent with the prescribed temperature profiles. Further inversion derives related emissions pathways for these concentrations. For this to happen, and to enable climate research centres to compare GHG concentrations and emissions estimates, common temperature trajectory scenarios are required. Here we define algebraic curves that asymptote to a stabilised limit, while also matching the magnitude and gradient of recent warming levels. The curves are deliberately parameter-sparse, needing the prescription of just two parameters plus the final temperature. Yet despite this simplicity, they can allow for temperature overshoot and for generational changes, for which more effort to decelerate warming change needs to be made by future generations. The curves capture temperature profiles from the existing Representative Concentration Pathway (RCP2.6) scenario projections by a range of different Earth system models (ESMs), which have warming amounts towards the lower levels of those that society is discussing.

Short summary
Recent UNFCCC climate meetings have placed much emphasis on constraining global warming to remain below 2 °C. The 2015 Paris meeting went further and gave an aspiration to fulfil a 1.5 °C threshold. We provide a flexible set of algebraic global temperature profiles that stabilise to either target. This will potentially allow the climate research community to estimate local climatic implications for these temperature profiles, along with emissions trajectories to fulfil them.
Final-revised paper