Global and regional temperature-change potentials for near-term climate forcers

Abstract

We examine the climate effects of the emissions of near-term climate forcers (NTCFs) from 4 continental regions (East Asia, Europe, North America and South Asia) using results from the Task Force on Hemispheric Transport of Air Pollution Source-Receptor global chemical transport model simulations. We address 3 aerosol species (sulphate, particulate organic matter and black carbon) and 4 ozone precursors (methane, reactive nitrogen oxides (NO_x), volatile organic compounds and carbon monoxide). We calculate the global climate metrics: global warming potentials (GWPs) and global temperature change potentials (GTPs). For the aerosols these metrics are simply time-dependent scalings of the equilibrium radiative forcings. The GTPs decrease more rapidly with time than the GWPs. The aerosol forcings and hence climate metrics have only a modest dependence on emission region. The metrics for ozone precursors include the effects on the methane lifetime. The impacts via methane are particularly important for the 20 yr GTPs. Emissions of NO_x and VOCs from South Asia have GWPs and GTPs of higher magnitude than from the other Northern Hemisphere regions. <br><br> The analysis is further extended by examining the temperature-change impacts in 4 latitude bands, and calculating absolute regional temperature-change potentials (ARTPs). The latitudinal pattern of the temperature response does not directly follow the pattern of the diagnosed radiative forcing. We find that temperatures in the Arctic latitudes appear to be particularly sensitive to BC emissions from South Asia. The northern mid-latitude temperature response to northern mid-latitude emissions is approximately twice as large as the global average response for aerosol emission, and about 20–30% larger than the global average for methane, VOC and CO emissions

Accounting for the climate–carbon feedback in emission metrics

“…Hansen et al, 2005). These two formulas, for AGWP and AGTP, are similar to those given by Collins et al (2013) in their Sect. 5.5, where they implicitly assume that γ r F (t) = δ(t), where is a constant.…”

“…5.5, where they implicitly assume that γ r F (t) = δ(t), where is a constant. Collins et al (2013) therefore assumed that the carbon sinks' response to a pulse of global temperature change was a pulse of size of CO 2 outgassing by the ocean and the terrestrial biosphere, but they did not justify this assumption. The next section investigates whether this assumption holds, and what functional form can be chosen for the dynamical function r F .…”

“…Aware of this limitation, the IPCC made a first attempt at including the climate-carbon feedback into metrics in a consistent manner. This attempt was based on an earlier study by Collins et al (2013), whose main object was not the climate-carbon feedback (but regionalized metrics). Our study is therefore an attempt to assess the robustness of these alternative but tentative metrics proposed by the IPCC (Myhre et al, 2013;Table 8.7).…”

The social cost of atmospheric release

“…Forcing by non-CO 2 emissions includes a component driven by the response of the carboncycle to temperature changes induced by those emissions (as in the calculations for CO 2 itself) based on a reduced carbon uptake of 1 GtC per degree warming (Arora et al 2013;Collins et al 2013b). The uncertainty in this effect is taken to be equal to the magnitude of the effect itself (Collins et al 2013b).…”

“…The uncertainty in this effect is taken to be equal to the magnitude of the effect itself (Collins et al 2013b).…”