IPCC AR5 WG3 (technical) Summary for Policymakers.
AR = Assessment Report
WG = Working Group
The Working Group III contribution to the IPCC’s Fifth Assessment Report (AR5) assesses literature on the scientific, technological, environmental, economic and social aspects of mitigation of climate change. It builds upon the Working Group III contribution to the IPCC’s Fourth Assessment Report (AR4), the Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN) and previous reports and incorporates subsequent new findings and research.
The report also assesses mitigation options at different levels of governance and in different economic sectors, and the societal implications of different mitigation policies, but does not recommend any particular option for mitigation. This Summary for Policymakers (SPM) follows the structure of the Working Group III report. The narrative is supported by a series of highlighted conclusions which, taken together, provide a concise summary. The basis for the SPM can be found in the chapter sections of the underlying report and in the Technical Summary (TS). References to these are given in square brackets.
The degree of certainty in findings in this assessment, as in the reports of all three Working Groups, is based on the author teams’ evaluations of underlying scientific understanding and is expressed as a qualitative level of confidence (from very low to very high) and, when possible, probabilistically with a quantified likelihood (from exceptionally unlikely to virtually certain). Confidence in the validity of a finding is based on the type, amount, quality, and consistency of evidence (e. g., data, mechanistic understanding, theory, models, expert judgment) and the degree of agreement. Probabilistic estimates of quantified measures of uncertainty in a finding are based on statistical analysis of observations or model results, or both, and expert judgment. Where appropriate, findings are also formulated as statements of fact without using uncertainty qualifiers. Within paragraphs of this summary, the confidence, evidence, and agreement terms given for a bolded finding apply to subsequent statements in the paragraph, unless additional terms are provided.
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Trends in stocks and flows of greenhouse gases and their drivers
Total anthropogenic GHG emissions have continued to increase over 1970 to 2010 with larger absolute decadal increases toward the end of this period (high confidence). Despite a growing number of climate change mitigation policies, annual GHG emissions grew on average by 1.0 gigatonne carbon dioxide equivalent (GtCO2 eq) (2.2 %) per year from 2000 to 2010 compared to 0.4 GtCO2eq (1.3 %) per year from 1970 to 2000 (Figure SPM.1). Total anthropogenic GHG emissions were the highest in human history from 2000 to 2010 and reached 49 (±4.5) GtCO2eq/yr in 2010. The global economic crisis 2007/2008 only temporarily reduced emissions. [1.3, 5.2, 13.3, 15.2.2, Box TS.5, Figure 15.1]
CO2 emissions from fossil fuel combustion and industrial processes contributed about 78 % of the total GHG emission increase from 1970 to 2010, with a similar percentage contribution for the period 2000–2010 (high confidence). Fossil fuel-related CO2 emissions reached 32 (±2.7) GtCO2/yr, in 2010, and grew further by about 3 % between 2010 and 2011 and by about 1–2 % between 2011 and 2012. Of the 49 (±4.5) GtCO2eq/yr in total anthropogenic GHG emissions in 2010, CO2 remains the major anthropogenic GHG accounting for 76 % (38 ± 3.8 GtCO2eq/yr) of total anthropogenic GHG emissions in 2010. 16 % (7.8 ± 1.6 GtCO2eq/yr) come from methane (CH4), 6.2 % (3.1 ± 1.9 GtCO2eq/yr) from nitrous oxide (N2O), and 2.0 % (1.0 ± 0.2 GtCO2eq/yr) from fluorinated gases (Figure SPM.1).
Annually, since 1970, about 25 % of anthropogenic GHG emissions have been in the form of non-CO2 gases.8 [1.2, 5.2]
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