As Earth's atmosphere heats up, scientists are working hard to determine the best way to keep things cool. While CO2 gets most of the headlines, it's not the only greenhouse gas out there, and many of them are substantially more dangerous pound for pound. Understanding the different atmospheric pollutants and how they stack up against CO2 will let you determine the most impactful way to focus your personal mitigation efforts.
Long-Lived Climate Pollutants (LLCPs)
Every greenhouse gas has its own atmospheric lifespan. Some, like CO2, can stay in the atmosphere for many years before they degrade or are absorbed. Although much of their warming potential comes from their lifespan, several GHGs also have a more potent effect on warming per ton than CO2.
As the most prevalent GHG, CO2 is the baseline comparator for all other gases. It's emitted primarily from burning fossil fuels like coal, natural gas, and oil. In addition, burning solid waste, trees, and other wood products is a large secondary source. Once it's out, CO2 can stay for hundreds of years in the atmosphere as part of an unbalanced carbon cycle.
Since the soil is a massive carbon bank, any disturbance to the land can also release CO2. Therefore, deforestation and soil degradation are high on the list of global warming culprits, while forest regrowth is one of the primary climate remediation strategies.
N2O rarely gets the press of CO2, but it is a potent enemy when human intervention has unbalanced the nitrous oxide budget. Like CO2, it can come from burning fossil fuels. In addition, it's emitted through many agricultural processes, particularly involving fertilizer. Since it's so potent, N2O wreaks havoc when soil erodes, and nitrogen plays a massive role in water pollution. On average, it stays in the atmosphere for about 100 years and is almost 275 times as potent as CO2 when it comes to Global Warming Potential (GWP)
Gases with fluorine are often emitted through industrial manufacturing, but they also find their way into the atmosphere through household and commercial aerosols and other chemicals. There are many fluorinated gases, but the most common are hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
Unfortunately, the prevalence of these gases comes from their original use as a replacement for chlorofluorocarbons, which deplete the ozone. As a result, their atmospheric impacts vary considerably, with some staying in the air for several days and others persisting for thousands of years. Moreover, some have a much more potent warming effect than CO2, most notably sulfur hexafluoride, which has a GWP of 25,200.
Short-Lived Climate Pollutants (SLCPs)
There are several potent GHGs that leave the atmosphere relatively quickly. Since they have such a high impact, but their mitigation can take effect quickly, many believe we should focus more on reducing them where possible.
Part of the reason people often disregard short-lived climate pollutants is that GWP is usually measured for a 100-year timeframe. However, SLCPs only last for a short time, and artificially stretching their impact that far gives an impression that they are not as dangerous as they actually are.
Methane (CH4) is the most common SLCP, and it has a 12-year atmospheric lifespan. Using the 100-year GWP, one ton of methane has the same global warming capacity as 21 tons of CO2. However, over 20 years, it's the same as 75 tons of CO2. To put it in perspective, methane currently causes about 30% of the warming that CO2 does, but accounts for a much smaller amount of GHG. Methane emissions come primarily from animal agriculture and refining fossil fuels.
As mentioned above, HFCs are fluorinated gasses, some of which clear out of the atmosphere within a few weeks. On average, this subgroup has a 15-year lifespan, but the GWPs can vary from 1,300 to 14,000. Perhaps most alarming is the fact that HFCs are the fastest-growing GHG, and their emissions rate will likely double within the next ten years. Their primary use is in refrigeration and aerosols, so technological advances that lead to alternative products or reliable reclamation will help reduce their impact.
Tropospheric ozone is not an immediate byproduct of industry or agriculture. Instead, it naturally forms from other pollutants that act as precursors. These gases include methane, carbon monoxide, and various nitrogen-based gases. Tropospheric ozone can change evaporation rates, cloud formation, and precipitation, while adversely affecting agricultural production. Although it remains present in the atmosphere only for a few days, it is responsible for the same amount of global warming as 20% of atmospheric CO2.
Black carbon is not a GHG. It is a particulate matter (PM) that comes from the incomplete burning of biomass and fossil fuels. The particles stay in the atmosphere for up to a few days, absorbing heat, causing health problems, and speeding up polar ice melt. For all its brief time in the air, black carbon is over 1,000 times as potent an atmospheric warmer as CO2.
Short and Long-Term Warming Threats Persist, but We Have the Tools to Fight Them
It is challenging to keep up with all the different atmospheric pollutants. Everyone is familiar with CO2, but many others are unfamiliar to most people. Unfortunately, a lower profile does not correlate to a lower climate impact, and the full range of short-lived and long-lived climate pollutants speeding the rate of global warming. Fortunately, awareness is growing, and many clever alternatives and reclamation strategies are available to help us do our part for a sustainable future.
Stay Insulated – HFCs and other fluorinated gases are common in refrigeration, cooling, foams, and aerosols. Of course, ensuring you have up-to-date and efficient appliances helps, but you can also use them as sparingly as possible to conserve energy and preserve coolant.
Big Picture – Global warming is complicated. Even if you have a newfound respect for SLCPs and want to do your best, don't forget that CO2 is still responsible for more warming than any other gas – and it can stay in the atmosphere for an incredibly long time. So don't lose sight of lowering carbon emissions, too!
Avoid Inefficient Fuels – Black carbon is nasty stuff that warms the planet and causes many serious health problems. Avoid burning fossil fuels whenever possible, and upgrade your car to an EV as soon as you can.