Improving Understanding of Future Chemically Active Greenhouse Gases?
Greenhouse gas emissions from fossil fuel combustion contribute to climate warming, but to better estimate the amount of warming, uncertainties about the concentrations and the climate response need to be addressed. Some greenhouse gases are chemically reactive in the atmosphere, have additional uncertainties about their chemical production and destruction, and may be potential targets for short-term mitigation. New DOE research at the University of California at Irvine has taken the first systematic look at the uncertainties in attributing and projecting human-driven increases in greenhouse gases. The Representative Concentration Pathways future emissions scenarios used in the current Intergovernmental Panel on Climate Change assessment have large uncertainties for methane (CH4, 25%) and nitrous oxide (N2O, 50%), and thus do not accurately project future abundances. The new study combines observational and model data with uncertainties that constrain the pre-industrial (natural) and current (natural + anthropogenic) greenhouse gas budgets. These data include pre-industrial abundances, current abundances and trends, lifetimes past and projected, and atmospheric distributions. Statistical methods were applied to assess, for the first time, the current budgets, anthropogenic fractions, and projected abundances with uncertainties. The methane lifetime was found to be 9.1 ± 0.9 years. Anthropogenic emissions contribute 64% of total emissions. N2O and CH4 emissions and abundances, including uncertainties, were also projected and values sometimes deviated from projections given by integrated assessment models. The research helps identify aspects of these chemical systems requiring further research and improves both the projections and mitigation potentials for greenhouse gases.
Prather, M. J., C. D. Holmes, and J. Hsu. 2012. “Reactive Greenhouse Gas Scenarios: Systematic Exploration of Uncertainties and the Role of Atmospheric Chemistry,” Geophysical Research Letters 39, L09803. DOI: 10.1029/2012GL051440.