Decades ago, had we gotten a handle on our CO2, our additional methane emissions might not have mattered — but those days are gone.
Human-caused methane emissions — the majority of which stem from food and agriculture waste, cow burps, and oil and gas operations — are responsible for half of the planet’s warming and are likely to cause temperatures to overshoot Paris targets in the coming decades. Recent UN research flags the importance of mitigating this greenhouse gas for stabilizing climate in the short term while potentially adding another, much-needed .5°C of wiggle room for warming from CO2.
But those days are gone. Continuously rising CO2 levels have pushed methane emissions above a threshold where the short-term warming they’ll cause could have dangerous impacts; there’s about two-and-a-half times more methane in the atmosphere now than before the Industrial Revolution.
Levels of the extra-potent greenhouse gas have thrown a wrench in the plans of climate scientists, as they’re seeing greater climate impacts from methane even at temperatures lower than predicted — “and that’s partially because the CO2 bathtub is so high now that there’s increased importance on the [methane] layer that’s on top,” Reinhardt said. “The really important point here is that cutting methane over the next few decades is really our only way of bringing temperatures down.”
According to the IPCC’s Sixth Assessment Report, human greenhouse gas emissions have caused the world to warm about 1.1° C. Methane — though with orders of magnitude less atmospheric concentration than CO2 — is responsible for half a degree of that warming. While it only hangs around in the atmosphere for 10-12 years, methane has about 30 times more warming force than CO2. Nonetheless, as long as anthropogenic methane emissions remain steady or increase, methane will continue to spend its short lifespan in the atmosphere making the planet hotter.
“CO2 is long lived — as you emit more CO2, the atmospheric impact continues to rise,” Reinhardt explained. “Methane is a bit different — the amount of warming in the atmosphere is more driven by the current rate of emissions of recent periods, rather than the accumulated emissions of decades or centuries.”
Think of it like a bathtub: As long as CO2 is turned on, the bathtub will continue to fill up — but most of the near-term warming will come from methane.
“We have a unique opportunity by mitigating emissions to actually see some of that warming go down, which is critically important to having manageable temperatures over the next century,” Reinhardt said.
One of the largest anthropogenic sources of methane, oil and gas infrastructure is particularly ripe for interventions that can be scaled now. Similarly, other heavy-emitting sectors have their own portfolio of mitigation strategies that should be enacted. But there’s still more to do if we want to fully “de-methanize.” And it needs to happen fast.
The future of methane
Like other greenhouse gases, methane itself isn’t the problem. Natural methane sources include marshland, termites, permafrost and more — it’s a natural product of various biological processes that have been going on as long as life itself. What’s not normal is how quickly we’re pushing ecosystems toward a methane-emitting tipping point.
“We have growing evidence that some of these systems are going to emit more methane than they were,” Reinhardt said. “Even though they’re natural emissions, they’re doing an unnatural thing.”
Scientists have been warning for years about a ticking “methane time bomb” in the thawing Arctic; and changes in temperature and precipitation in tropical wetlands are also being studied closely. Reinhardt urges immediate and sweeping action to eliminate human-caused methane emissions to stave off potentially disastrous cascading effects, as well as secure a half-degree buffer against future warming.
“Given the time sensitivity that we have here, it’s really important that we mitigate what we can with the solutions we have available today while also investing in [further] solution development,” Reinhardt said.
One of those solutions will tackle the problem of aerosols (defined here as a suspension of particles in the atmosphere vs the propellant used in spray cans), which help to mask the effects of climate change. Ironically, as we decarbonize, fewer aerosols will be co-produced — meaning greenhouse gases will have an even greater impact in the future than they do now. Aerosols such as sulfur dioxide are largely co-emitted with CO2. Sulfur dioxide’s lifespan is on the order of days, not decades; so, when aerosols stop being emitted, warming is immediately accelerated. That doesn’t cancel the mandate to decarbonize, Reinhardt asserts; but the world should expect rapidly accelerated warming as masking aerosols stop being emitted.
“People are increasingly worried that the next few years we’re going to be seeing much faster warming than what has happened in the past,” she said.
But removing our methane emissions could help flatten the heating bump as aerosols fizzle out of the atmosphere.
Unfortunately, the methane discussion is still relatively new; so measuring and predicting its effects often gets wedged into metrics optimized for CO2. Reinhardt and others are calling for different ways to measure global warming potential of various greenhouse gases, with separate metrics for long-lived (ex: CO2) and short-lived (ex: methane) gases. Policy wonks and scientists are still debating what kind of a metric should be developed for short-lived gases such as methane; but they agree that we should be setting both long-term and short-term goals as opposed to single, cumulative metrics such as global warming potential (GWP).
“We should be setting separate targets for long-lived and short-lived climate pollutants, so that we can best ensure that we are controlling both and not creating tradeoffs,” Reinhardt said.