[Source: Science, full page: (LINK). Abstract, edited.]
The human imperative of stabilizing global climate change at 1.5°C
O. Hoegh-Guldberg1,2,*, D. Jacob3, M. Taylor4, T. Guillén Bolaños3, M. Bindi5, S. Brown6,7, I. A. Camilloni8, A. Diedhiou9, R. Djalante10,11, K. Ebi12, F. Engelbrecht13, J. Guiot14, Y. Hijioka15, S. Mehrotra16, C. W. Hope17, A. J. Payne18, H.-O. Pörtner19, S. I. Seneviratne20, A. Thomas21,22, R. Warren23, G. Zhou24
1 Global Change Institute, University of Queensland, St. Lucia, QLD 4072, Australia. 2 School of Biological Sciences, University of Queensland, St. Lucia, QLD 4072, Australia. 3 Climate Service Center Germany (GERICS), Helmholtz-Zentrum Geesthacht, Hamburg, Germany. 4 Department of Physics, University of the West Indies, Kingston, Jamaica. 5 Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, 50144 Firenze, Italy. 6 Faculty of Engineering and Physical Sciences, University of Southampton, Boldrewood Innovation Campus, Southampton SO16 7QF, UK. 7 Department of Life and Environmental Sciences, Faculty of Science and Technology, Bournemouth University, Fern Barrow, Poole, Dorset BH12 5BB, UK. 8 Centro de Investigaciones del Mar y la Atmósfera (UBA-CONICET), UMI-IFAECI/CNRS, and Departamento de Ciencias de la Atmósfera y los Océanos (FCEN), University of Buenos Aires, Buenos Aires, Argentina. 9 Université Grenoble Alpes, French National Research Institute for Sustainable Development (IRD), CNRS, Grenoble INP, IGE, F-38000 Grenoble, France. 10 United Nations University–Institute for the Advanced Study of Sustainability (UNU-IAS), Tokyo, Japan. 11 Halu Oleo University, Kendari, South East Sulawesi, Indonesia. 12 Center for Health and the Global Environment, University of Washington, Seattle, WA, USA. 13 Global Change Institute, University of the Witwatersrand, Johannesburg 2193, South Africa. 14 Aix Marseille University, CNRS, IRD, INRA, Collège de France, CEREGE, Aix-en-Provence, France. 15 Center for Climate Change Adaptation, National Institute for Environmental Studies, Onogawa, Tsukuba, Ibaraki 305-8506, Japan. 16 World Bank, Washington, DC, USA. 17 Cambridge Judge Business School, University of Cambridge, Cambridge, UK. 18 University of Bristol, Bristol, UK. 19 Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany. 20 Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland. 21 Climate Analytics, 10961 Berlin, Germany. 22 Environmental and Life Sciences, University of the Bahamas, Nassau 76905, Bahamas. 23 Tyndall Centre for Climate Change Research and School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK. 24 State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081, China.
*Corresponding author. Email: email@example.com
Science 20 Sep 2019: Vol. 365, Issue 6459, eaaw6974 / DOI: 10.1126/science.aaw6974
The need to stabilize global climate
Climate change will be the greatest threat to humanity and global ecosystems in the coming years, and there is a pressing need to understand and communicate the impacts of warming, across the perspectives of the natural and social sciences. Hoegh-Guldberg et al. review the climate change–impact literature, expanding on the recent report of the Intergovernmental Panel on Climate Change. They provide evidence of the impacts of warming at 1°, 1.5°, and 2°C—and higher—for the physical system, ecosystems, agriculture, and human livelihoods. The benefits of limiting climate change to no more than 1.5°C above preindustrial levels would outweigh the costs.
Science, this issue p. eaaw6974
The United Nations Framework Convention on Climate Change (UNFCCC) was established in 1992 to pursue the “stabilization of greenhouse gas concentrations at a level that would prevent dangerous anthropogenic interferences with the climate system.” Since 1992, five major climate change assessment cycles have been completed by the UN Intergovernmental Panel on Climate Change (IPCC). These reports identified rapidly growing climate-related impacts and risks, including more intense storms, collapsing ecosystems, and record heatwaves, among many others. Once thought to be tolerable, increases in global mean surface temperature (GMST) of 2.0°C or higher than the pre-industrial period look increasingly unmanageable and hence dangerous to natural and human systems.
The Paris Climate Agreement is the most recent attempt to establish international cooperation over climate change. This agreement, ratified or acceded to by 185 countries, was designed to bring nations together voluntarily to take ambitious action on mitigating climate change, while also developing adaptation options and strategies as well as guaranteeing the means of implementation (e.g., climate finance). The Agreement is aimed at “holding the increase in the global average temperature to well below 2.0°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change.” Many unanswered questions regarding a 1.5°C target surround the feasibility, costs, and inherent risks to natural and human systems. Consequently, countries invited the IPCC to prepare a Special Report on “the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty.” The Special Report was completed and approved by the 48th Session of the IPCC in October 2018.
Multiple lines of evidence indicate that the next 0.5°C above today (which will take GMST from 1.0°C to 1.5°C above the pre-industrial period) will involve greater risks per unit temperature than those seen in the last 0.5°C increase. This principle of “accelerating risk” is also likely to drive proportionally and possibly exponentially higher risk levels in the transition from 1.5°C to 2.0°C above the pre-industrial period. We argue that this is a consequence of impacts accelerating as a function of distance from the optimal temperature for an organism or an ecosystem process. Coral reefs, for example, often appear healthy right up until the onset of mass coral bleaching and mortality, which can then destroy a reef within a few months. This also explains the observation of “tipping points” where the condition of a group of organisms or an ecosystem can appear “healthy” right up to the point of collapse, suggesting caution in extrapolating from measures of ecosystem condition to predict the future. Information of this nature needs to be combined with an appreciation of organisms’ distance from their optimal temperature.
Finally, we explore elements of the costs and benefits associated with acting in response to climate change, and come to the preliminary conclusion that restraining average global temperature to 1.5°C above the pre-industrial period would be much less costly than the damage due to inaction on global climate change.
As an IPCC expert group, we were asked to assess the impact of recent climate change (1.0°C, 2017) and the likely impact over the next 0.5° to 1.0°C of additional global warming. At the beginning of this exercise, many of us were concerned that the task would be hindered by a lack of expert literature available for 1.5°C and 2.0°C warmer worlds. Although this was the case at the time of the Paris Agreement, it has not been our experience 4 years later. With an accelerating amount of peer-reviewed scientific literature since the IPCC Special Report Global Warming of 1.5°C, it is very clear that there is an even more compelling case for deepening commitment and actions for stabilizing GMST at 1.5°C above the pre-industrial period.
Increased concentrations of atmospheric greenhouse gases have led to a global mean surface temperature 1.0°C higher than during the pre-industrial period. We expand on the recent IPCC Special Report on global warming of 1.5°C and review the additional risks associated with higher levels of warming, each having major implications for multiple geographies, climates, and ecosystems. Limiting warming to 1.5°C rather than 2.0°C would be required to maintain substantial proportions of ecosystems and would have clear benefits for human health and economies. These conclusions are relevant for people everywhere, particularly in low- and middle-income countries, where the escalation of climate-related risks may prevent the achievement of the United Nations Sustainable Development Goals.
Keywords: Climate Change; Global Warming; International cooperation.