Less than 2 °C warming by 2100 unlikely

Abstract

The recently published Intergovernmental Panel on Climate Change (IPCC) projections to 2100 give likely ranges of global temperature increase in four scenarios for population, economic growth and carbon use1. However these projections are not based on a fully statistical approach. Here we use a country-specific version of Kaya’s identity to develop a statistically-based probabilistic forecast of CO2 emissions and temperature change to 2100. Using data for 1960-2010, including the UN’s probabilistic population projections for all countries2–4, we develop a joint Bayesian hierarchical model for GDP per capita and carbon intensity. We find that the 90% interval for cumulative CO2 emissions includes the IPCC’s two middle scenarios but not the extreme ones. The likely range of global temperature increase is 2.0–4.9°C, with median 3.2°C and a 5% (1%) chance that it will be less than 2°C (1.5°C). Population growth is not a major contributing factor. Our model is not a “business as usual” scenario, but rather is based on data which already show the effect of emission mitigation policies. Achieving the goal of less than 1.5°C warming will require carbon intensity to decline much faster than in the recent past.

A New Composite Index for Greenhouse Gases: Climate Science Meets Social Science

“…It extends the FCCC efforts to respond to the threat of climate change by setting internationally binding emission reduction targets that aim to force countries to reduce their greenhouse gas emissions sufficiently to keep global warming this century beneath 2 • C above pre-industrial levels, with an aspirational target of 1.5 • C. As at October 2017, 169 of 197 parties to the FCCC have ratified the Agreement, although on 1 June 2017, one of the ratifying countries, the United States, declared its intention to withdraw from the Agreement (Ironically, the 2 • C target was initially proposed by an economist, William D. Nordhaus, in a series of papers in the 1970s, and based on the amount of global warming experienced since pre-industrial times; see, for example, [1]. The likelihood of achieving the Paris Agreement objective in this century is viewed skeptically by [2], and the sensitivity of the likelihood of achieving the objective to the definition of "pre-industrial" is explored by [3] (For a brief history of the international response to climate change see http://unfccc.int/essential_background/items/6031.php. A list of parties to the FCCC, and their ratification status, is available at http://unfccc.int/paris_agreement/items/9444.php).…”

“…A GWP is a globally averaged cumulative warming potential of a greenhouse gas, integrated over a period of time, occurring from the emission of a unit mass of the gas relative to that of the reference gas, CO 2 , which has a GWP of 1. The IPCC specifies horizons of 20, 100 and 500 years.…”

“…The Kyoto Protocol permits countries to meet part of their emission reduction obligations by cutting back on gases other than CO 2 . This requires a definition of trade-offs among the radiatively active gases.…”

“…The Kyoto Protocol to the United Nations Framework Convention on Climate Change (FCCC), adopted in 1997 and entered into force in 2005, sets reduction targets on the anthropogenic CO 2 -equivalent emissions of CO 2 , methane (CH 4 ), nitrous oxide (N 2 O) and the F group of gases (The F group of gases consists of 13 hydrofluorocarbons (HFCs), 7 perfluorocarbons (PFCs) and sulfur hexafluoride (SF 6 )). CO 2 emissions arise as a by-product of fossil fuel (coal, oil and gas) combustion, biomass burning and industrial processes such as the production of cement.…”

Interspecific Hybridization May Provide Novel Opportunities for Coral Reef Restoration

“…The Great Barrier Reef (GBR) is no exception with 50-80% coral mortality recorded on many northern reefs following the 2016 mass bleaching event (Great Barrier Reef Marine Park Authority, 2017), followed by another high mortality mass bleaching event in 2017. Climate models predict a <5% chance of reaching the Paris agreement target of limiting the global temperature rise to <2 • C compared to pre-industrial times by 2100 (Raftery et al, 2017), and most coral reefs are forecasted to experience annual severe bleaching before the end of the century . Several observations of an increase in tolerance of coral bleaching after successive bleaching events suggest that adaptation and/or acclimatization are possible under certain conditions (Maynard et al, 2008;Berkelmans, 2009;Guest et al, 2012;Penin et al, 2013).…”