The regional temperature implications of strong air quality measures

Borgar Aamaas,Bjørn Hallvard Samset,Terje Koren Berntsen

doi:10.5194/acp-19-15235-2019

Borgar Aamaas, Bjørn Hallvard Samset + Show 1 more

Open Access

https://doi.org/10.5194/acp-19-15235-2019

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Abstract

Abstract. Anthropogenic emissions of short-lived climate forcers (SLCFs) affect both air quality and climate. How much regional temperatures are affected by ambitious SLCF emission mitigation policies is, however, still uncertain. We investigate the potential temperature implications of stringent air quality policies by applying matrices of regional temperature responses to new pathways for future anthropogenic emissions of aerosols, methane (CH4), and other short-lived gases. These measures have only a minor impact on CO2 emissions. Two main options are explored, one with climate optimal reductions (i.e., constructed to yield a maximum global cooling) and one with the maximum technically feasible reductions. The temperature response is calculated for four latitude response bands (90–28∘ S, 28∘ S–28∘ N, 28–60∘ N, and 60–90∘ N) by using existing absolute regional temperature change potential (ARTP) values for four emission regions: Europe, East Asia, shipping, and the rest of the world. By 2050, we find that global surface temperature can be reduced by -0.3±0.08 ∘C with climate-optimal mitigation of SLCFs relative to a baseline scenario and as much as −0.7 ∘C in the Arctic. Cutting CH4 and black carbon (BC) emissions contributes the most. The net global cooling could offset warming equal to approximately 15 years of current global CO2 emissions. On the other hand, mitigation of other SLCFs (e.g., SO2) leads to warming. If SLCFs are mitigated heavily, we find a net warming of about 0.1 ∘C, but when uncertainties are included a slight cooling is also possible. In the climate optimal scenario, the largest contributions to cooling come from the energy, domestic, waste, and transportation sectors. In the maximum technically feasible mitigation scenario, emission changes from the industry, energy, and shipping sectors will cause warming. Some measures, such as those in the agriculture waste burning, domestic, transport, and industry sectors, have large impacts on the Arctic, especially by cutting BC emissions in winter in areas near the Arctic.

Highlights

Poor air quality is an issue of global concern, with health and welfare impacts affecting billions of people (WHO, 2016; Dockery et al, 1993; Di et al, 2017)
Emissions are given for seven short-lived climate forcers (SLCFs): black carbon (BC), organic carbon (OC), sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO), volatile organic compounds (VOC), and methane (CH4)
This study has not analyzed scenarios with CO2 mitigation or measures on SLCFs that will result in emission cuts of CO2

Summary

Introduction

Poor air quality is an issue of global concern, with health and welfare impacts affecting billions of people (WHO, 2016; Dockery et al, 1993; Di et al, 2017). Many of the components that make up air pollution lead to radiative forcing, impacting climate through scattering or absorbing solar radiation or by acting as greenhouse gases (Myhre et al, 2013b; von Schneidemesser et al, 2015). The net and individual climate impacts of present emissions of such short-lived climate forcers (SLCFs) have been extensively studied, but they are still poorly constrained (Stohl et al, 2015; Aamaas et al, 2016; Myhre et al, 2017; Samset et al, 2018). CH4, which is a greenhouse gas and a precursor of O3 and stratospheric water vapor, is the SLCF that gives the largest warming at current emission levels.

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