Other Emissions of Greenhouse Gases and Aerosols

I only cover three other types of emissions besides energy related CO2. I thought of including black carbon but in the end decided to skip it as I already have too many papers. I resisted the temptation to try to include two of my papers in the collection, though I ended up discussing my paper more below :) I also include a graphic that will not be appearing in our book. It is from Smith et al. (2011) and compares the various estimates of sulfur emissions.

Deforestation and land-use change is an important source of emissions of CO2. Levels of emissions are much lower than from energy related sources, more stable over time, but also very uncertain. Houghton (2003) presents estimates of CO2 emissions from land-use change from 1850 to 2000, globally and by region. In general the tend rises from 1 to 2 Gt C over the 150 years with an acceleration in the trend around 1950 in common with emissions from energy related sources. Therefore, there is a clear link with economic growth. Tropical deforestation, particularly in Asia and Latin America dominates. In recent decades there is net reforestation in developed countries. Unusually, the data are increasingly uncertain in recent decades with estimates from different researchers varying substantially (Houghton, 2010).

The third most important greenhouse gas in the atmosphere and the second most important anthropogenic source is methane. Relatively little work has been done on CH4 in comparison to CO2. Stern and Kaufmann (1996) used available data to reconstruct the first time series of historic emissions from 1860-1993. They found that anthropogenic emissions had increased from 80 million tonnes of carbon in 1860 to 380 million in 1990. The relative importance of the various emissions sources changed over time though rice farming and livestock husbandry remained the two most important sources.

Offsetting the radiative forcing due to greenhouse gases is a significant negative forcing due to aerosols derived from sulphur oxide (primarily dioxide) emissions. These aerosols do not persist in the atmosphere for usually more than a few days and so the source of emissions is important and effects are localized though they spread far beyond the sources to affect neighbouring countries. The main sources of anthropogenic sulphur emissions are the combustion of coal and metal smelting. Stern (2006) showed that that after increasing fairly steadily from 1850 to the early 1990s global emissions began to trend downwards. Emissions in Western Europe and North America as well as Japan had already been trending down since 1970 primarily due to policies to reduce acid rain (Stern, 2005). But this decline was offset by growth in other regions. Following 1990, there was a dramatic reduction in emissions from Eastern Europe and the former Soviet Union. The likelihood that emissions will continue to decline in the future will contribute to future warming. Whereas Stern (2006) uses a combination of previously published data and model estimates, Smith et al. (2011) provide an inventory of sulphur emissions from 1850 to 2005 using a uniform methodology. The results largely confirm Stern’s (2006) findings though the levels are generally lower by a few percent.

References

Houghton, R. A. (2003) Revised estimates of the annual net flux of carbon to the atmosphere from changes in land use and land management 1850-2000, Tellus 55B: 378-390.

Houghton, R. A. (2010) How well do we know the flux of CO2 from land use change? Tellus 62B: 337-351.

Smith, S. J., J. van Ardenne, Z. Klimont, R. J. Andres, A. Volke, S. D. Arias (2011) Anthropogenic sulfur dioxide emissions: 1850-2005, Atmospheric Chemistry and Physics 11: 1101-1116.

Stern D. I. (2005) Beyond the environmental Kuznets curve: Diffusion of sulfur-emissions-abating technology, Journal of Environment and Development 14(1), 101-124.

Stern D. I. (2006) Reversal in the trend of global anthropogenic sulfur emissions, Global Environmental Change 16(2), 207-220.

Stern D. I. and R. K. Kaufmann (1996) Estimates of global anthropogenic methane emissions 1860-1993, Chemosphere 33, 159-176.