Abatement of Greenhouse Gases: Does Location Matter? |
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Authors: | Terje Berntsen Jan Fuglestvedt Gunnar Myhre Frode Stordal Tore F Berglen |
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Institution: | 1. CICERO, Center for International Climate and Environmental Research, P.O. Box 1129, Blindern, N-0318, Oslo, Norway 2. Norwegian Institute for Air Research (NILU), Norway 3. Department of Geosciences, University of Oslo, Norway
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Abstract: | Today's climate policy is based on the assumption that the location of emissions reductions has no impact on the overall climate
effect. However, this may not be the case since reductions of greenhouse gases generally will lead to changes in emissions
of short-lived gases and aerosols. Abatement measures may be primarily targeted at reducing CO2, but may also simultaneously reduce emissions of NOx, CO, CH4 and SO2 and aerosols. Emissions of these species may cause significant additional radiative forcing. We have used a global 3-D chemical
transport model and a radiative transfer model to study the impact on climate in terms of radiative forcing for a realistic
change in location of the emissions from large-scale sources. Based on an assumed 10% reduction in CO2 emissions, reductions in the emissions of other species have been estimated. Climate impact for the SRES A1B scenario is
compared to two reduction cases, with the main focus on a case with emission reductions between 2010 and 2030, but also a
case with sustained emission reductions. The emission reductions are applied to four different regions (Europe, China, South
Asia, and South America). In terms of integrated radiative forcing (over 100 yr), the total effect (including only the direct
effect of aerosols) is always smaller than for CO2 alone. Large variations between the regions are found (53–86% of the CO2 effect). Inclusion of the indirect effects of sulphate aerosols reduces the net effect of measures towards zero. The global
temperature responses, calculated with a simple energy balance model, show an initial additional warming of different magnitude
between the regions followed by a more uniform reduction in the warming later. A major part of the regional differences can
be attributed to differences related to aerosols, while ozone and changes in methane lifetime make relatively small contributions.
Emission reductions in a different sector (e.g. transportation instead of large-scale sources) might change this conclusion
since the NOx to SO2 ratio in the emissions is significantly higher for transportation than for large-scale sources. The total climate effect
of abatement measures thus depends on (i) which gases and aerosols are affected by the measure, (ii) the lifetime of the measure
implemented, (iii) time horizon over which the effects are considered, and (iv) the chemical, physical and meteorological
conditions in the region. There are important policy implications of the results. Equal effects of a measure cannot be assumed
if the measure is implemented in a different region and if several gases are affected. Thus, the design of emission reduction
measures should be considered thoroughly before implementation. |
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