15: Technologies for Super Pollutants Mitigation
- Page ID
- 41711
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)V. RAMANATHAN UC San Diego, Scripps Institution of Oceanography, DURWOOD ZAELKE UC Santa Barbara and Institute of Governance & Sustainable Development and JONATHAN COLE Mira Costa College
- Explain the importance of rapid action to mitigate super pollutants, also known as short-lived climate pollutants (SLCPS). You will learn how mitigation of black carbon, methane, tropospheric ozone, and hydrofluorocarbons (HFCs) can have a powerful and relatively rapid impact to bend the warming curve because of the large contributions of these climate pollutants to current global warming (>40%) and their short atmospheric lifetimes. You will be able to explain some of the main benefits of immediate action to reduce emissions of these short-lived climate pollutants.
- Describe and evaluate measures to bend the curves of black carbon, methane, and ozone. Next, you will learn about specific measures to mitigate emissions of black carbon and methane. Mitigation of methane will also reduce levels of tropospheric ozone, a potent greenhouse gas. You will be able to describe how reduction of these substances can contribute to human health, food security, and climate justice.
- Describe and evaluate measures to bend the HFC curve, including the Montreal Protocol and other policy instruments. You will learn how the Montreal Protocol, a 1987 international agreement that was designed to protect the stratospheric ozone layer, has also resulted in significantly reduced warming from greenhouse gases such as chlorofluorocarbons (CFCs). You will be able to explain how the 2016 Kigali Amendment to the Montreal Protocol goes further and has the potential to avoid up to 0.5°C of warming by 2100 by mandating the global phasedown of HFCs, a class of powerful greenhouse gases. Finally, you will learn how parallel efforts to improve energy efficiency of air conditioning and other cooling equipment can double the climate benefits of the HFC phasedown.
Overview
This chapter focuses on Solution #9 from the Bending the Curve report, part of the technology-based solutions cluster:
Immediately make maximum use of available technologies and regulations to reduce methane emissions by 50% and black carbon emissions by 90%. Phase out hydrofluorocarbons by 2030 by amending the Montreal Protocol.
The last few chapters have discussed technologies and policies to bend the warming curve by reducing emissions of carbon dioxide (CO2). However, as discussed in Chapter 4, the benefits of CO2 mitigation will not be felt for at least a decade or two, and CO2 mitigation alone will not be enough to keep us below the 2°C threshold of dangerous warming, nor the more prudent 1.5ºC threshold.
Moreover, decreasing CO2 emissions by transitioning away from fossil fuels might have the paradoxical effect of increasing global warming in the short term. Fossil fuels contain sulfur and other impurities. Their combustion results in the formation of sulfate aerosols in the atmosphere. Efforts to reduce sulfates have been under way for several decades because of their damaging effects on human health and natural ecosystems, but these aerosols also reflect sunlight, causing a cooling effect that partly offsets the warming from carbon dioxide. As the use of fossil fuels decreases, the loss of sulfate aerosol cooling will be felt almost immediately, while the warming effects of the emitted CO2 will take decades or even centuries to diminish.
In this chapter, we will explore a complementary solution: reducing a key group of warming agents knows as super pollutants or shortlived climate pollutants (SLCPs) to bend the warming curve quickly (over a few decades) while we pursue CO2 mitigation to bend the curve in the long term (over several decades to centuries). Combined, these efforts, if enacted by 2020, give us a significant chance (about 90% probability) of keeping warming well below 2°C (aiming for 1.5°C) in this century and beyond.
Figure 15.1 summarizes the properties of the four short-lived climate pollutants we’ll be considering: black carbon particles (a major component of soot), the greenhouse gases methane and tropospheric ozone (not to be confused with the beneficial ozone in the stratosphere), and hydrofluorocarbons (HFCs). These four warming agents are called short-lived climate pollutants (SLCPs) because their typical lifetimes in the atmosphere range from about a week to 15 years, compared with hundreds or thousands of years for CO2 (see Box 1.3.1 in Chapter 1 for a discussion of atmospheric lifetimes and warming potentials of greenhouse gases). Reducing emissions of these substances quickly brings down their concentrations in the atmosphere. For example, if all black carbon particle emissions were eliminated today, black carbon would disappear from the atmosphere within a few weeks.
We will mostly use the scientific term SLCPs in the rest of this chapter, but these four climate pollutants are often called super pollutants because of their strong warming effects. It has been recognized since 1975 that these warming agents are much more potent, pound for pound, than CO2. The warming effect of gases is measured in terms of their global warming potential (GWP), which is defined in Box 1.3.1 in Chapter 1. Methane is about 30 times more powerful than CO2, black carbon is 500 to 2,000 times more powerful, and HFCs produce from 1,000 to over 4,000 times more warming on a 100-year time scale.
As detailed later in this chapter, mitigation of these SLCPs, if completed by 2030, can bend the warming curve by up to 0.6°C by 2050 (about 0.4°C from methane mitigation, 0.1°C from black carbon, and 0.1°C from HFCs), cutting the rate of projected warming by about half compared with “business as usual” and reducing the projected sea level rise between 2020 and 2050 by 20%. We can summarize the required emissions reductions as “80/40/100”: an 80% reduction for black carbon; a 40% reduction for methane; and a complete phaseout of high GWP HFCs. By 2100, these measures combined could avoid up to 1.2°C warming. For comparison, aggressive CO2 mitigation would avoid about 0.1ºC to 0.3°C by 2050 and up to 1.9°C by 2100.
| Methane | Black Carbon | HFCs |
|---|---|---|
| Degasification recovery & use | Improve stoves (biomass to LPG/biogas, wood to pellet) |
Low-GWP, high energyefficiency alternatives for refrigeration, air conditioning, and foam blowing |
| Recovery from municipal waste and wastewater treatment | Upgrade brick kilns | Efficacy for cooling technologies |
| Reduce emissions from agriculture | Use particle filters for diesel vehicles | |
| Solutions | Solutions | Solutions |
| 16 measures, including those listed above: |
No "one-size-fits-all" solution | |
| \(\approx-40 \%\) methane, \(\approx-80 \% \mathrm{BC}\) in 2030 (rel. to BAU) | Further R\&D for superefficient and affordable cooling equipment | |
|
No technical breakthroughs needed |
||
| Already implemented in many countries | ||
| Half reductions at low cost or cost-neutral | ||
Figure 15.2 Short-lived climate pollutant measures. BC = black carbon; BAU = business as usual; R&D = research and development. Adapted from the Climate and Clean Air Coalition; data from UNEP and WMO. 2011.
In this chapter, we will describe some of the available measures to produce the required 80/40/100 reductions in emissions of black carbon, methane, and HFCs, some of the most effective of which are highlighted in Figure 15.2. While many more SLCP mitigation measures are possible—a 2011 study by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) examined over 2,000 of them—the key measures discussed in this chapter account for 90% of the avoided warming. These measures are based on existing technologies and do not require new technical breakthroughs.
It’s important to note that the sources of SLCPs as well as the measures for emissions reductions are highly dependent on the region under consideration. For Africa and Asia, the critical measures include reducing black carbon emissions from biomass cookstoves and diesel vehicles as well as reducing methane emissions from coal, oil, and gas production and municipal waste. For North America and Europe, the key mitigation measures include reducing methane emissions from oil and gas production, long-distance natural gas transmission pipelines, and municipal waste as well as reducing black carbon emissions from residential biomass heating, shipping activities, and open agricultural biomass burning.
You may have noticed that we have not discussed mitigation measures for tropospheric ozone emissions. This is because ozone is not directly emitted by human activities; we will see later in this chapter that measures to reduce methane emissions and fossil fuel combustion will significantly decrease ozone as well.
The final sections of this chapter cover the phasedown of HFCs under the Kigali Amendment to the Montreal Protocol, an international treaty signed in 1987 to phase out substances that deplete the ozone layer. Generally considered the world’s most successful environmental treaty, the Montreal Protocol solved the first great threat to the global atmosphere by phasing out chlorofluorocarbons (CFCs) and related fluorinated gases and by putting the ozone layer on the path to recovery in the 2030s. At the same time, because CFCs and other fluorinated gases are also powerful climate pollutants, the success of the Montreal Protocol has avoided warming that would have grown to equal or surpass the warming caused by CO2 today. The success of the Montreal Protocol is continuing with the Kigali Amendment, which was approved in 2016 and entered into force at the beginning of 2019.