Introduction: The problem with methane
Some stories have come out recently about the melting of permafrost in the Arctic. Of course, one reason we’re worried about thawing permafrost is that the process releases methane into the atmosphere. I’ve written about methane previously, but here’s a summary of the relative impact of methane versus CO2 as a greenhouse gas.
For an equivalent amount of CO2, methane immediately traps at least 100 times as much as CO2. But the methane starts to break down and leave the atmosphere relatively quickly. As more time goes by, and as more of that original ton of methane disappears, the steady warming effect of the CO2 slowly closes the gap. Over 20 years, the methane would trap about 80 times as much heat as the CO2. Over 100 years, that original ton of methane would trap about 25 times as much heat as the ton of CO2.
The upshot is, any increase in methane emissions is a problem. In the next decade or so, an important way to keep the global mean temperature increase at or below 1.5oC is to effectively address methane emissions. Without such efforts, it will be difficult to impossible to meet that goal.
Global Warming and Positive Feedbacks
There have been demonstrated plenty of what are called positive feedbacks in the climate system that exacerbate global warming. Generally, a positive feedback is the amplification of one phenomenon by another phenomenon caused by the first one. Examples in global warming include
- The positive feedback from snowpack laying for less time in the cold season
- The positive feedback from increased evaporation and water vapor content in the atmosphere as the atmosphere warms.
- Water vapor is an effective greenhouse gas, so the increase in temperature is reinforced by the increased water vapor, and the resulting warming further increases atmospheric water vapor.
We already are seeing increases in methane emissions from the Arctic, as discussed in previous Climate Brief diaries. Here’s a list of some of them going back to last summer:
- The People of Siberia Are Choking on Acrid Wildfire Smoke Due to Unrelenting Heatwave
- Methane Knob “Easiest to Turn” To Slow Down Global Warming
- Record Levels of the Greenhouse Gas Methane
- Methane, Wildfires and Drought, Oh My!
- Massive Bursts of Methane Plumes All Over the U.S. With Little Explanation As to Why
Arctic Precipitation and Global Warming
Climate models forced by increased greenhouse gas concentrations have consistently shown that precipitation will increase in the Arctic as a result of greater amounts of water vapor resulting from increased temperatures. Recent Climate Model Intercomparison Project (CMIP) experiments with the newest climate models (CMIP6) increase Arctic precipitation even more than the previous set (CMIP5) ...
...due to greater global warming and poleward moisture transport, greater Arctic amplification and sea-ice loss and increased sensitivity of precipitation to Arctic warming.
Causes of these results are consistent with global warming physics and dynamics. Additionally, the trends noted here are consistent with what has been observed, and what retrospective runs with the CMIP5 and 6 models have shown, from 1980 to 2005. Note that model similarity to observations is a prerequisite for their use in climate projections.
We show the increase in Arctic rainfall as a fraction of total precipitation in each season for the CMIP5 versus CMIP6 by the year 2100 in the table below. This information is from the same article quoted above.
| Experiments | CMIP5 (OLD) | CMIP6 (New) |
|---|---|---|
| winter | 260 | 422 |
| spring | 141 | 261 |
| Summer | 51 | 71 |
| Fall | 192 | 268 |
So what does this mean in terms of permafrost melt?
Increased Rainfall vs Snowfall Melts Permafrost More Quickly
The banner graphic to this diary shows an experiment being run by the Wageningen University (Netherlands) where a wet summer season was simulated by irrigating the permafrost soil with water. What would be the effect of such an experimental simulation?
The scientists expected to see some increase in permafrost melting and some accompanying effects, that would end once the next cold season arrived. Indeed, there was a 35% increase in melt compared to permafrost that wasn’t so treated. However, the effect of an extremely wet summer lasted for several years; even two years after the sprinkler test, the permafrost under the irrigated sites was still thawing faster. This effect was enhanced further during periods of combined heavy rainfall and high air temperatures.
Conclusions
An author of the study put the conclusions quite succinctly:
“If we only take warmer temperatures into account, we will underestimate how much permafrost is thawing as a result of climate change, and how much extra CO2 and methane is being released …. But it is difficult to realistically represent the effect of such precipitation extremes on permafrost thaw and greenhouse gas emissions in climate models.
Scientists working on the global warming problem could underestimate future greenhouse gas emissions caused by permafrost thaw, which in turn could render the 1.5-2oC of global warming under possibly greenhouse gas reduction scenarios too optimistic.
Plans are to address regional variations in sensitivity of permafrost to rain, to help make more reliable estimates of future permafrost thaw.