Working Group I: The Scientific Basis


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II.2.5: Tropospheric O3 burden (global mean column in DU)
Year A1B A1T A1FI A2 B1 B2 A1p A2p B1p B2p IS92a IS92a/SAR
1990 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0
2000 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.0 34.3
2010 35.8 35.6 35.8 35.7 34.8 35.2 36.2 35.6 34.3 35.4 35.5 34.8
2020 37.8 37.7 38.4 38.2 35.6 36.7 38.8 38.2 35.4 37.1 37.1 35.3
2030 39.3 40.3 41.5 40.8 35.9 38.4 40.5 40.7 35.7 38.5 38.7 35.8
2040 39.7 41.9 45.1 42.6 35.8 39.8 41.3 42.4 36.5 39.9 40.1 36.5
2050 39.8 42.9 49.6 44.2 35.0 40.7 41.6 44.1 37.5 40.6 41.6 37.1
2060 39.6 43.1 51.9 45.7 34.0 41.5 41.8 45.6 37.7 41.2 42.9 37.7
2070 39.1 41.9 53.8 47.2 33.1 42.1 41.4 47.1 37.9 41.6 44.0 38.2
2080 38.5 40.2 55.9 49.3 32.1 43.0 40.8 49.1 38.1 42.3 45.1 38.7
2090 38.0 38.4 55.6 52.0 31.2 43.7 39.9 51.8 36.8 42.6 46.1 39.1
2100 37.5 36.5 55.2 54.8 30.1 44.2 38.9 54.7 35.2 42.8 47.2 39.5

Note: IS92a/SAR column refers to IS92a emissions as reported in the SAR which estimated this O3 change only as an indirect feedback effect from CH4 increases; whereas IS92a column uses the latest models (see Chapter 4) which include also changes in emissions of NOx, CO and VOC. A mean tropospheric O3 content of 34 DU in 1990 is adopted; and 1 ppb of tropospheric O3 = 0.65 DU.
These projected increases in troposheric O3 are likely to be 25% too large, see note to Table 4.11 of Chapter 4 describing corrections made after government review.

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