Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse
gases are the highest in history. Recent climate changes have had widespread impacts
on human and natural systems. 1
1. Each finding is grounded in an evaluation of underlying evidence and agreement. In many cases, a synthesis of evidence and agreement supports an
assignment of confidence. The summary terms for evidence are: limited, medium or robust. For agreement, they are low, medium or high. A level of
confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, e.g., medium confidence. The following
terms have been used to indicate the assessed likelihood of an outcome or a result: virtually certain 99–100% probability, very likely 90–100%,
likely 66–100%, about as likely as not 33–66%, unlikely 0–33%, very unlikely 0–10%, exceptionally unlikely 0–1%. Additional terms (extremely
likely 95–100%, more likely than not >50–100%, more unlikely than likely 0–<50%, extremely unlikely 0–5%) may also be used when appropriate.
Assessed likelihood is typeset in italics, e.g., very likely. See for more details: Mastrandrea, M.D., C.B. Field, T.F. Stocker, O. Edenhofer, K.L. Ebi, D.J. Frame,
H. Held, E. Kriegler, K.J. Mach, P.R. Matschoss, G.-K. Plattner, G.W. Yohe and F.W. Zwiers, 2010: Guidance Note for Lead Authors of the IPCC Fifth Assessment
Report on Consistent Treatment of Uncertainties, Intergovernmental Panel on Climate Change (IPCC), Geneva, Switzerland, 4 pp.
Anthropogenic greenhouse gas emissions have increased since the pre-industrial era, driven
largely by economic and population growth, and are now higher than ever. This has led to atmospheric
concentrations of carbon dioxide, methane and nitrous oxide that are unprecedented in
at least the last 800,000 years. Their effects, together with those of other anthropogenic drivers,
have been detected throughout the climate system and are extremely likely to have been
the dominant cause of the observed warming since the mid-20th century. {1.2, 1.3.1}
The evidence for human influence on the climate system has grown since the IPCC Fourth Assessment Report (AR4). It is
extremely likely that more than half of the observed increase in global average surface temperature from 1951 to 2010 was
caused by the anthropogenic increase in GHG concentrations and other anthropogenic forcings together. The best estimate
of the human-induced contribution to warming is similar to the observed warming over this period (Figure SPM.3). Anthropogenic
forcings have likely made a substantial contribution to surface temperature increases since the mid-20th century
over every continental region except Antarctica4
. Anthropogenic influences have likely affected the global water cycle since
1960 and contributed to the retreat of glaciers since the 1960s and to the increased surface melting of the Greenland ice
sheet since 1993. Anthropogenic influences have very likely contributed to Arctic sea-ice loss since 1979 and have very likely
made a substantial contribution to increases in global upper ocean heat content (0–700 m) and to global mean sea level rise
observed since the 1970s. {1.3, Figure 1.10}
It is virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily
and seasonal timescales, as global mean surface temperature increases. It is very likely that heat waves will occur with a
higher frequency and longer duration. Occasional cold winter extremes will continue to occur. {2.2.1}
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http://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf
..Just like carbon tax ..
