IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group I: The Physical Science Basis

Figure 2.3. Recent CO2 concentrations and emissions. (a) CO2 concentrations (monthly averages) measured by continuous analysers over the period 1970 to 2005 from Mauna Loa, Hawaii (19°N, black; Keeling and Whorf, 2005) and Baring Head, New Zealand (41°S, blue; following techniques by Manning et al., 1997). Due to the larger amount of terrestrial biosphere in the NH, seasonal cycles in CO2 are larger there than in the SH. In the lower right of the panel, atmospheric oxygen (O2) measurements from flask samples are shown from Alert, Canada (82°N, pink) and Cape Grim, Australia (41°S, cyan) (Manning and Keeling, 2006). The O2 concentration is measured as ‘per meg’ deviations in the O2/N2 ratio from an arbitrary reference, analogous to the ‘per mil’ unit typically used in stable isotope work, but where the ratio is multiplied by 106 instead of 103 because much smaller changes are measured. (b) Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr–1 (black) through 2005, using data from the CDIAC website (Marland et al, 2006) to 2003. Emissions data for 2004 and 2005 are extrapolated from CDIAC using data from the BP Statistical Review of World Energy (BP, 2006). Land use emissions are not shown; these are estimated to be between 0.5 and 2.7 GtC yr–1 for the 1990s (Table 7.2). Annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red) are also shown (Keeling et al, 2005). The isotope data are expressed as δ13C(CO2) ‰ (per mil) deviation from a calibration standard. Note that this scale is inverted to improve clarity.

Table 2.3. The direct aerosol radiative effect (DRE) estimated from satellite remote sensing studies (adapted and updated from Yu et al., 2006). Reference Instrumenta Data Analysed Brief Description Clear Sky DRE(W m–2) ocean Bellouin et al. (2005) tMODIS; TOMS; SSM/I 2002 MODIS fine and total τaer with TOMS Aerosol Index and SSM/I todiscriminate dust from sea salt. –6.8Loeb and Manalo-Smith (2005) CERES; MODIS Mar 2000 to Dec 2003 CERES radiances/irradiances and angular distribution models and aerosol properties from either MODIS or fromNOAA-NESDISb algorithm used toestimate the direct radiative effect. –3.8 (NESDIS)to –5.5 (MODIS) Remer and Kaufman (2006) MODIS Aug 2001 to Dec 2003 Best-prescribed aerosol model fitted to MODIS data. τaer from fine-mode fraction. –5.7 ± 0.4Zhang et al. (2005); Christopher and Zhang (2004) CERES; MODIS Nov 2000 to Aug 2001 MODIS aerosol properties, CERES radiances/irradiances and angulardistribution models used to estimate thedirect radiative effect. –5.3 ± 1.7Bellouin et al. (2003) POLDER Nov 1996 to Jun 1997 Best-prescribed aerosol model fitted to POLDER data –5.2Loeb and Kato (2002) CERES; VIRS Jan 1998 to Aug 1998; Mar 2000. τaer from VIRS regressed against the TOA CERES irradiance (35°N to 35°S) –4.6 ± 1.0Chou et al. (2002) SeaWiFs 1998 Radiative transfer calculations with SeaWiFS τaer and prescribed opticalproperties –5.4Boucher and Tanré (2000) POLDER Nov 1996 to Jun 1997 Best-prescribed aerosol model fitted to POLDER data –5 to –6Haywood et al. (1999) ERBE Jul 1987 to Dec 1988 DRE diagnosed from GCM-ERBE TOA irradiances –6.7Mean (standard deviation) –5.4 (0.9) Notes: a SSM/I: Special Sensor Microwave/Imager; VIRS: Visible Infrared Scanner; ERBE: Earth Radiation Budget Experiment. b NESDIS: National Environmental Satellite, Data and Information Service.