Observations: Atmosphere and Surface (original) (raw)

Climate Change 2013 – The Physical Science Basis

The evidence of climate change from observations of the atmosphere and surface has grown significantly during recent years. At the same time new improved ways of characterizing and quantifying uncertainty have highlighted the challenges that remain for developing long-term global and regional climate quality data records. Currently, the observations of the atmosphere and surface indicate the following changes: Atmospheric Composition It is certain that atmospheric burdens of the well-mixed greenhouse gases (GHGs) targeted by the Kyoto Protocol increased from 2005 to 2011. The atmospheric abundance of carbon dioxide (CO 2) was 390.5 ppm (390.3 to 390.7) 1 in 2011; this is 40% greater than in 1750. Atmospheric nitrous oxide (N 2 O) was 324.2 ppb (324.0 to 324.4) in 2011 and has increased by 20% since 1750. Average annual increases in CO 2 and N 2 O from 2005 to 2011 are comparable to those observed from 1996 to 2005. Atmospheric methane (CH 4) was 1803.2 ppb (1801.2 to 1805.2) in 2011; this is 150% greater than before 1750. CH 4 began increasing in 2007 after remaining nearly constant from 1999 to 2006. Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF 6) all continue to increase relatively rapidly, but their contributions to radiative forcing are less than 1% of the total by well-mixed GHGs. {2.2.1.1} For ozone-depleting substances (Montreal Protocol gases), it is certain that the global mean abundances of major chlorofluorocarbons (CFCs) are decreasing and HCFCs are increasing. Atmospheric burdens of major CFCs and some halons have decreased since 2005. HCFCs, which are transitional substitutes for CFCs, continue to increase, but the spatial distribution of their emissions is changing. {2.2.1.2} Because of large variability and relatively short data records, confidence 2 in stratospheric H 2 O vapour trends is low. Near-global satellite measurements of stratospheric water vapour show substantial variability but small net changes for 1992-2011. {2.2.2.1} It is certain that global stratospheric ozone has declined from pre-1980 values. Most of the decline occurred prior to the mid 1990s; since then ozone has remained nearly constant at about 3.5% below the 1964-1980 level. {2.2.2.2} Confidence is medium in large-scale increases of tropospheric ozone across the Northern Hemisphere (NH) since the 1970s. 1 Values in parentheses are 90% confidence intervals. Elsewhere in this chapter usually the half-widths of the 90% confidence intervals are provided for the estimated change from the trend method. 2 In this Report, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: 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. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Section 1.4 and Box TS.1 for more details). 3 In this Report, 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%, and Extremely unlikely 0-5%) may also be used when appropriate. Assessed likelihood is typeset in italics, e.g., very likely (see Section 1.4 and Box TS.1 for more details). Confidence is low in ozone changes across the Southern Hemisphere (SH) owing to limited measurements. It is likely 3 that surface ozone trends in eastern North America and Western Europe since 2000 have levelled off or decreased and that surface ozone strongly increased in East Asia since the 1990s. Satellite and surface observations of ozone precursor gases NO x , CO, and non-methane volatile organic carbons indicate strong regional differences in trends. Most notably NO 2 has likely decreased by 30 to 50% in Europe and North America and increased by more than a factor of 2 in Asia since the mid-1990s.