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
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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
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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
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