Greenhouse gas growth rates

Abstract

We posit that feasible reversal of the growth of atmospheric CH4 and other trace gases would provide a vital contribution toward averting dangerous anthropogenic interference with global climate. Such trace gas reductions may allow stabilization of atmospheric CO 2 at an achievable level of anthropogenic CO2 emissions, even if the added global warming constituting dangerous anthropogenic interference is as small as 1°C. A 1°C limit on global warming, with canonical climate sensitivity, requires peak CO 2 Ϸ 440 ppm if further non-CO 2 forcing is ؉0.5 W͞m 2 , but peak CO2 Ϸ 520 ppm if further non-CO 2 forcing is ؊0.5 W͞m 2 . The practical result is that a decline of non-CO 2 forcings allows climate forcing to be stabilized with a significantly higher transient level of CO 2 emissions. Increased ''natural'' emissions of CO2, N2O, and CH4 are expected in response to global warming. These emissions, an indirect effect of all climate forcings, are small compared with human-made climate forcing and occur on a time scale of a few centuries, but they tend to aggravate the task of stabilizing atmospheric composition.

Equivalent CO2 and its use in understanding the climate effects of increased greenhouse gas concentrations

“…These were provided by the NASA Goddard Institute for Space Studies (GISS) (Hansen and Sato, 2004). The histories of the global mean greenhouse gas concentrations can be found at www.giss.nasa.gov/ modelforce/ghgases/.…”

“…CH 3 Br concentrations were from the NOAA Earth System Research Laboratory (Montzka et al, 2003). The global mean dataset for the main wellmixed greenhouse gases (CO 2 , CH 4 and N 2 O) and HFCs, PFCs and SF 6 were all derived from averages of a mixture of data from air trapped in polar ice sheets and in-situ flask data (more details are given in the supporting material for Hansen and Sato (2004)). The global mean data were provided as a time history going back to 1850 in the case of the main well-mixed greenhouse gases and going back to 1930 for the HFCs, PFCs and SF 6 .…”

Climate change and trace gases

“…Hansen & Sato (2004) argue that large release from methane hydrates is unlikely if additional global warming is kept under 18C, based on the fact that CH 4 increase was moderate during previous interglacial periods that were warmer than at present by up to 18C. However, warming greater than 18C raises the likelihood of a large positive feedback from methane hydrates.…”

“…(a) Greenhouse gas forcing and Vostok temperature: Antarctic temperature (left scale) from Vostok ice core ( Vimeux et al 2002) and global climate forcing (right scale) due to CO 2 , CH 4 and N 2 O. Forcing zero point is for 1850 gas amounts specified by Hansen & Sato (2004). Temperature zero point is 'present' value from the Vostok ice core ( Vimeux et al 2002).…”

Good enough tools for global warming policy making

“…The remarkable year-to-year variability of the airborne fraction is discussed in . Historical observational data of the fraction: annual increase of the carbon content of the atmosphere divided by the quantity of carbon in annual emissions of CO 2 from fossil fuels (Hansen & Sato 2004;updated in Hansen 2006). appendix A.…”