Climate forcing growth rates: doubling down on our Faustian bargain

• Published in: Environmental research letters 2013-03, Vol.8 (1), p.11006-9
• Main Authors: Hansen, James, Kharecha, Pushker, Sato, Makiko
• Format: Article
• Language: English
• Subjects: Aerosols; Air pollution; Anomalies; Anthropogenic factors; Atmosphere; Atmospheric circulation; Bark; Biogeochemistry; Biosphere; Black carbon; Boreal forests; Burning; Carbon cycle; Carbon dioxide; Carbon dioxide emissions; Carbon sinks; Carbon sources; Chemical transport; Climate change; Climate system; Coal; Coal-fired power plants; Combustion; Concrete; Cooling; Cowlings; Data interpretation; Deciduous forests; Deforestation; Deposition; Drying; Dust; El Nino; Fertilization; Forests; Fossil fuels; Global warming; Greenhouse effect; Greenhouse gases; Human influences; Interference; Intergovernmental Panel on Climate Change; Land use; Mathematical analysis; Methane; Montreal Protocol; Nitrogen; Nitrogen cycle; Nutrients; Optical thickness; Photosynthesis; Primary production; Reserves; Sensitivity; Solar radiation; Southern Oscillation; Systems analysis; Terrestrial ecosystems; Trends; Tropical environment; Troposphere; Volcanic eruptions; Volcanoes
• ISSN: 1748-9326; 1748-9326
• DOI: 10.1088/1748-9326/8/1/011006

Rahmstorf et al ’s (2012) conclusion that observed climate change is comparable to projections, and in some cases exceeds projections, allows further inferences if we can quantify changing climate forcings and compare those with projections. The largest climate forcing is caused by well-mixed long-lived greenhouse gases. Here we illustrate trends of these gases and their climate forcings, and we discuss implications. We focus on quantities that are accurately measured, and we include comparison with fixed scenarios, which helps reduce common misimpressions about how climate forcings are changing. Annual fossil fuel CO 2 emissions have shot up in the past decade at about 3% yr -1 , double the rate of the prior three decades (figure 1). The growth rate falls above the range of the IPCC (2001) ‘Marker’ scenarios, although emissions are still within the entire range considered by the IPCC SRES (2000). The surge in emissions is due to increased coal use (blue curve in figure 1), which now accounts for more than 40% of fossil fuel CO 2 emissions. Figure 1. CO 2 annual emissions from fossil fuel use and cement manufacture, an update of figure 16 of Hansen (2003) using data of British Petroleum (BP 2012) concatenated with data of Boden et al (2012). The resulting annual increase of atmospheric CO 2 (12-month running mean) has grown from less than 1 ppm yr -1 in the early 1960s to an average ~2 ppm yr -1 in the past decade (figure 2). Although CO 2 measurements were not made at sufficient locations prior to the early 1980s to calculate the global mean change, the close match of global and Mauna Loa data for later years suggests that Mauna Loa data provide a good approximation of global change (figure 2), thus allowing a useful estimate of annual global change beginning with the initiation of Mauna Loa measurements in 1958 by Keeling et al (1973). Figure 2. Annual increase of CO 2 based on data from the NOAA Earth System Research Laboratory (ESRL 2012). CO 2 change and global temperature change are 12-month running means of differences for the same month of consecutive years. Nino index (Nino3.4 area) is 12-month running mean. Both temperature indices use data from Hansen et al (2010). Annual mean CO 2 amount in 1958 was 315 ppm (Mauna Loa) and in 2012 was 394 ppm (Mauna Loa) and 393 ppm (Global). Interannual variability of CO 2 growth is correlated with ENSO (El Nino Southern Oscillation) variations of tropical temperatures (figure 2). Ocean–atmosphere CO 2 exchang