The emissions of CO2 and methane continue to rise. Methane is the second most important greenhouse gas after CO2. It is responsible for one third of the warming so far. To limit long-term warming, we must stop net CO2 emissions within a few decades. However, reducing methane emissions has a more immediate effect. This is because methane stays in the atmosphere for much shorter periods than CO2. Recently, we can now see from space, using satellites, where a lot of methane is being emitted. The United Nations uses this information to urge governments and companies responsible for these emissions to seal these methane leaks.

CO2 reduction is crucial for the long term

When it comes to limiting warming, most attention is focused on CO2. There is a good reason for this: CO2, which is released by the combustion of fossil fuels and deforestation, is responsible for the majority of warming. Warming will only stop when we (net) no longer emit CO2, but it takes hundreds to even thousands of years for the amount of CO2 in the atmosphere to return to its natural level with the corresponding lower temperature.

Because the amount of CO2 in the atmosphere reacts so slowly, it takes time for a lower CO2 emission to affect warming. The amount of CO2 in the atmosphere - and thus warming - will only slowly reverse if we reduce emissions. For methane, this is different.

Reduction of methane has a quick effect

Methane is relatively quickly chemically broken down in the atmosphere and therefore remains in the atmosphere for only about 10 years. The amount of methane reacts quite quickly to reduced emissions, unlike CO2. By the way, a residence time of 10 years is still much longer than most forms of air pollution. For example, nitrogen oxides only stay in the air for a few hours before being chemically broken down, and fine particulate matter for a few days or at most weeks before it settles or rains out. The shorter the residence time in the atmosphere, the faster the amount decreases when emissions decrease. If the emissions of nitrogen oxides are suddenly significantly reduced, as happened during the corona lockdowns, the air will be much cleaner the next day. And vice versa: when we start emitting again, the air will quickly become as dirty as it was.

It works the same way for methane, but on a timescale of years – much shorter than for CO2. If we significantly reduce methane emissions, the amount in the atmosphere will noticeably decrease in the following years. And thus, warming will be mitigated much faster than with a comparable reduction in CO2 emissions. And with constant emissions, the amount of methane does not increase anymore and the associated warming stops. With CO2, constant emissions will still cause the amount of CO2 to rise and the associated warming as well. The relationship between emissions and warming of CO2 and methane is schematically represented in Figure 1.