Short-Lived Pollutants: Why Is It So Crucial To Reduce Their Prevalence?

Methane

Methane is a powerful greenhouse gas emitted by both natural and manmade sources. It remains in the atmosphere for only about 12 years on average but, as previously mentioned, warms the planet 86 times as much as carbon dioxide over a 20-year period. It’s generally considered the second-most important greenhouse gas after carbon dioxide, and emissions are growing at an increasing rate. The Environmental Defense Fund estimates that methane accounts for at least 25% of today’s global warming.

One key variable is whether those increases in methane concentrations have been driven by nature-based sources or manmade processes. Manmade sources of methane include leakage from fossil fuel infrastructure (like pipelines), landfills, various industrial processes, and cattle production. Of these manmade emissions, roughly 35% comes from leaks of methane from fossil fuels, mainly through extraction and transport, 20% comes from waste, and over 40% comes from agriculture.

The latter source—cow burps—is particularly noteworthy. There are about one billion cows around the world, and they collectively generate about 40% of global methane emissions. But methane is also released by natural sources like Arctic permafrost, and many scientists are worried that manmade climate change will induce tipping points like permafrost melt that will amplify methane emissions from these sources in a way that can’t be as easily controlled. Global warming will also quicken the decomposition of organic material, which emits methane if done in water. If tropical wetlands become wetter and warmer, which is a distinct possibility, more methane emissions are possible. Recent research has validated these concerns, showing that biological sources of methane are a primary driver of post-2006 increases in methane emissions.

In essence, by destabilizing natural processes, we are limiting nature’s ability to clean up our mess. Plus, we’re unleashing a degree of uncertainty that challenges our ability to combat the climate crisis, no matter how much technological advancement we achieve over the coming decades. Tipping points related to methane, like permafrost melt, represent just some of the many harrowing examples of this trend.

The World Meteorological Organization (WMO) recently released a sobering study on the same day as a new U.N. report that says the world’s governments haven’t committed to cutting enough carbon emissions, putting the world on track for a 2.5°C increase in global temperatures by the end of the century. According to the WMO report, relative to preindustrial times, carbon dioxide concentrations in 2021 were 49% higher, methane levels were 162% higher, and nitrous oxide levels were 24% higher.

Just before 2021’s COP26 gathering, the United States and European Union took the lead in promoting the Global Methane Pledge, which targets a 30% reduction in atmospheric methane by 2030. It has over 100 signatories representing nearly 50% of global anthropogenic methane emissions and over two-thirds of the global GDP. But there remain many notable holdouts, including China.

The aforementioned WMO report estimates that lowering atmospheric methane levels by 30% by 2030, which is the stated goal of the Global Methane Pledge, could shave 0.2°C off the rise in temperatures that would otherwise take place. Put differently, International Energy Agency Executive Director Fatih Birol has said that cutting global methane emissions from human activities by 30% by the end of the 2020s “would have the same effect on global warming by 2050 as shifting the entire transport sector to net zero CO2 emissions.”

The U.N. estimates that nearly half of the roughly 380 million metric tons of methane released by human activities annually can be cut this decade with available and largely cost-effective methods mostly related to agricultural production and fossil fuel production. Doing so would avoid nearly 0.3°C of warming by the 2040s.

Methane frankly doesn’t get the level of worldwide scrutiny it deserves both as an agent of atmospheric chaos and as a way for us to quickly abate a lot of global warming. And similarly to decarbonization, methane reductions would bring a plethora of ancillary benefits that have nothing to do with the climate crisis.

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Hydrofluorocarbons

Excessive UV radiation poses a number of threats, from skin cancer to immune system suppression to crop damage and widespread environmental harm. In 1985, scientists working in Antarctica made a startling discovery that incited global panic: the stratospheric ozone layer, which protects Earth from excessive UV radiation, was thinning rapidly. The cause of this trend was clear: chlorofluorocarbons (CFCs). These chemicals were present in everything from aerosol cans (like hairspray) to refrigerators to solvents. Left unchecked, scientists worried that CFCs would destroy the ozone layer within a few decades. Their discovery quickly galvanized international negotiations on a global treaty to ban CFCs. This led to the Montreal Protocol, which was agreed upon and opened for signature in 1987 before going into force in 1989.

The Montreal Protocol has often been hailed as the most successful international agreement in history. CFC consumption declined from over 800,000 metric tons per year in the 1980s to an estimated 156 metric tons in 2014. Experts estimate that by 2050, the ozone layer will be as strong as was in 1980.

Since the Montreal Protocol came into effect, global consumption of ozone-depleting substances has fallen mightily. But the global need for what these substances provide - namely heat transfer - hasn’t abated. As such, hydroflurocarbons (HFCs) have largely replaced CFCs. Like CFCs, HFCs are a group of industrial chemicals primarily used for cooling and refrigeration. Many HFCs are powerful greenhouse gases, and even though they only last between 15 and 29 years in the atmosphere, they pack quite a warming punch when they’re high in the skies. The most abundant HFC is 3,790 times more damaging to the climate over a 20-year period than carbon dioxide. That’s not a typo.

While HFCs don’t deplete the ozone layer (since they lack ozone-depleting chlorine), their warming potential nonetheless makes them very dangerous. Nearly 140 countries have ratified the Kigali Amendment to the Montreal Protocol, which calls for a gradual reduction in global HFC use (with more time given to poorer and warmer countries).

HFCs are a sensitive climate topic given the lack of cost-effective alternatives for developing countries that will depend on substances like HFCs both to grow their economies and to mitigate the disproportionate impacts they will suffer from climate change. But alternatives do exist, and global cooperation (and assistance from wealthier countries) could go a long way toward lowering HFC emissions and curtailing the greenhouse effect.

Conclusion

Since SLCPs tend to come from similar sources, the ways to lessen their emissions tend to overlap. For instance, in agriculture, this includes better manure management, banning open-field burning of agriculture waste, and improving field aeration (particularly for rice). In waste, this includes upgrading wastewater treatment and improving waste management by separating and then treating biodegradable municipal waste and collected landfill gas. In the fossil fuel supply chain, this includes reducing leakage from gas pipelines and ensuring recovery and utilization of gas. In residential and industrial areas, this includes transitioning from traditional cooking and heating methods with cleaner biomass and pellet stoves. In transportation, this includes installing particulate filters on-road and off-road vehicles, not to mention moving away from internal combustion engines.

These fixes can provide some breathing room in the fight against the climate crisis. Scientists estimate that immediate action on SLCPs could help prevent 0.4°C of global warming and cut sea level rise by a quarter to a half. As the infamous 1.5°C threshold outlined in the Paris Agreement approaches, SLCPs can help meet this moment to limit warming in combination with long-term adaptation efforts.

Decarbonization rightfully gets the lion’s share of attention in regard to climate solutions. But SLCPs deserve plenty of focus, and reducing their prevalence would be a massive win-win for humans and the planet. A combination of ongoing and nascent SLCP solutions could alleviate a significant amount of global warming while making the world a healthier place for us and for the abundant forms of life we share this planet with.