Waste management, as a policy, brings the complementary emissions reductions required to reduce global warming, says the Intergovernmental Panel on Climate Change's new report (IPCC AR6 WGI) released on August 9. The statement is a huge step towards reducing emissions and a major departure from previous IPCC reports.
The waste sector emits methane (CH4), a potent greenhouse gas (GHG), through the decomposition of waste in dumps and landfills. While 82 times stronger than carbon dioxide (C02) after 20 years, for being a short-lived gas, methane was incorrectly thought to have a marginal role in global warming. Solutions reducing short-lived gases, such as effective waste management, have not been viewed as critical to mitigate climate change as solutions that reduce long-lived greenhouse gases. That all changed with the recent IPCC Report that places equal importance on limiting long- and short-lived GHGs, including methane.
GHGs effect on global warming - ten years sooner than expected
The new 4,000-page IPCC report breaks the news that human influence on the climate system is now an established fact and that a global temperature increase of 1.5ºC is likely to be reached in the early 2030s, ten years earlier than previously assessed. This reduced timetable factors in an increased concentration of emissions from human activities that more quickly accelerates global warming – by creating a GHG effect that traps excess energy (see Figure 1).
According to the IPCC, global warming is responsible for changes in the climate system, such as "increases in the frequency and intensity of hot extremes, marine heatwaves and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost" (IPCC AR6 WGI, page 20. Fig. 2).
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| Figure 1. The Earth's energy budget and energy loss / IPCC AR6 WGI, p. 1816 / Graphic by IPCC |
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| Figure 2. Possible climate futures |
The importance of near-term time scales & short-lived GHGs in limiting global warming
The IPCC has adamantly stated that reducing emissions is essential to limit global warming and stabilise climate systems. It has, however, focused its attention on reducing emissions with long-term effects on climate, such as CO2, as recommended by long-term time scales.
For scientists in creating their forecast models, metrics and time scales matter when it comes to understanding the effect of a GHG. There are several metrics and time scales. Global Air Temperature Change, for instance, measured over a 100-year period is largely affected by CO2, while in a period of 10 years methane plays a significant role in temperature change (fig. 3). Although 100-year time scales have been most prominently used in previous climate assessments, the new IPCC report leaves it to policymakers to decide which time scale - and emission metric - is most applicable to their needs.
The IPCC report’s invitation to use near-term time scales closely relates to short-lived GHGs or Short-lived Climate Forcers (SLCFs), the GHG group that mostly affects climate over a 10- to 20-year period.
It has taken scientists a while to understand the effects of SCLFs on climate. Previous science thought that SLCFs’ reductions lead to disbenefits for near-term climate change, because aerosols, a SLCF gas, have cooling effects and were believed to drive the overall effect of SLCFs as a multigas. This is no longer the case and the new IPCC report confirms that changes in SLCFs will very likely cause further warming in the next two decades, and that the influence of SLCFs on global temperature is at least as large as that of CO2 (IPCC AR6 WGI, p. 110).
This is an important statement. It means that a previously underrated GHG group has been pointed up as key to limiting warming to 1.5ºC in the near term. And this is where the IPCC report identifies waste management’s increased role in global warming mitigation, through its effectiveness in reducing methane, the main contributor to SLCFs.
SLCFs affect climate and are, in most cases, also air pollutants. They include aerosols, which are also called particulate matter (PM), and chemically reactive gases (methane, ozone, some halogenated compounds, nitrogen oxides, carbon monoxide, non-methane volatile organic compounds, sulphur dioxide and ammonia). Except for methane and some halogenated compounds whose lifetimes are about a decade or more, SLCFs only persist in the atmosphere from a few hours to a couple of months." (IPCC AR6 WGI, p. 1429)
Until the 1950s, the majority of SLCFs emissions originated from North America and Europe. Since the 1990s more than 50% of anthropogenic SLCFs originate from Asia.
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| Figure 3. Global surface temperature change 10 and 100 years after a one year pulse of present day emissions / IPCC AR6 WGI, p. 178 / Graph by IPCC |
Waste management is essential to cut methane emissions
Methane is a powerful short-lived gas that stays in the atmosphere for 12 years. Its global warming potential is highest when the gas enters the atmosphere and sharply declines with time. Methane is so powerful that after 20 years its warming potential is still 82 times greater than carbon dioxide’s (IPCC AR6 WGI, p. 1739).
Methane emissions are growing since 2007 at a growth rate of 7 +/- 3 ppb per year. With an effective radiating forcing (ERF) of 0.54 Wm-2, methane has an attributed contribution to global mean surface air temperature (GSAT) of +0.3ºC (IPCC AR6 WGI, p. 1798).
The main sources of anthropogenic methane are agriculture (livestock production and rice cultivation), fossil fuel production and distribution, waste decomposition in landfills and dumps, and biomass burning (fig. 4).
The waste sector generates 55-77 Tg of CH4 emissions per year, that is, 18% of global anthropogenic methane emissions, a large enough share to help limit global warming if they were to be avoided.
Although the agricultural and fossil fuel sectors offer the largest mitigation potential, they aren’t quite there with full-fledged, viable solutions to cut emissions. The agricultural sector hasn't got a large-scale alternative to the high-polluting meat industry, and the fossil fuel sector needs massive investments that aren't available due to divestment policies. The waste sector, on the contrary, has already proven practices and technologies in place to cut its methane emissions. Practices such as waste management in combination with energy recovery and recycling can end landfills and dumps – the sector main emitters – slash methane emissions, and positively impact climate stabilisation with the co-benefit of improved air quality.
In sum, by phasing out landfill and dumps, the world has a way to reduce methane emissions, which the IPCC report clearly says will lessen the newly-revised – negative – impact of SLCFs and help limit global warming to 1.5ºC.
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| Figure 4. Data by IPCC AR6 WGI, Table 5.2, p. 1189 / Graphic by PS |
