April 13, 2007

Methane Matters

We all know the story – humans are burning fossil fuels, greenhouse gases are increasing in atmospheric concentration at an alarming rate, the temperature of the earth is soaring upward, the ecosystems are struggling to cope with all the related changes, and if we don’t act now, we will soon push the entire system past the dreaded tipping point. We at World Climate Report have presented evidence from a growing number of scientific papers that challenge this simple but highly popularized and publicized global warming story. Now another recent paper calls into question one of the most basic assumption – the article questions whether the second most important greenhouse gas, namely methane, is continuing to increase in atmospheric concentration.

There is no doubt that fossil fuel burning around the world is causing an increase in atmospheric carbon dioxide (CO2) concentration, and CO2 remains the number one anthropo-generated greenhouse gas. The second most important of these greenhouse gases is methane (CH4), and the greenhouse crusade wants you and everyone else to believe that methane is increasing in atmospheric concentration, various human activities are responsible, and we need policies to reduce emissions from animals, termites, rice paddies, landfills, coal mines, wetlands, and so on.

If you examine the staggering 1.7 million websites that are identified searching for “Methane and Global Warming,” you will discover that methane may be the very gas to push us past the tipping point sometime in the near future. You will be warned that melting permafrost will release enormous quantities of methane gas that will escape from unstable methane hydrate deposits in the Arctic, and when this occurs, the earth will experience a runaway greenhouse effect. You will discover scientists who are far more concerned about methane than CO2. Given all the claims that the permafrost is melting, the release of methane from the Arctic should be well underway.

To add to the scare, you will discover that methane is far more powerful as a greenhouse gas than CO2 – the same mass of methane would warm the earth 23 times more than the same mass of CO2. According to the Intergovernmental Panel on Climate Change (IPCC), methane concentration has increased by 150% (increased by 2.5 times) since 1750 and it accounts for 20% of the total radiative forcing from all the long-lived and globally mixed greenhouse gases. In the overwhelming majority of the IPCC future greenhouse gas scenarios, the methane concentration at the end of this century is presumed to be much greater than it is currently. In the global warming literature, methane is a major player and potentially the grim reaper that someday may destroy the world as we know it.

Well, here is the latest twist to the methane story – methane is not increasing in atmospheric concentration! We have highlighted this fact many times before at World Climate Report, and a new article in Environmental Science and Technology reveals that global methane concentration is not behaving the way the IPCC and the global warming advocates would have us believe. The Khalil et al. team from Portland State University and the Oregon Graduate Institute start the article interestingly noting “Methane concentrations in the atmosphere have more than doubled over the last century, raising concerns that it is contributing to global warming and will continue to do so in the future. Although these past increases were alarmingly rapid, subsequent measurements showed a persistent slowdown in the trends to nearly zero at present.” Notice that in their second sentence, they fully acknowledge what we have been saying for years – the actual data indicate that atmospheric methane concentration is not increasing, despite what many assume in running climate models to simulate future conditions. We can tell a climate model to assume some rate of increase in methane, and the model will undoubtedly tell us that in response, the world warms. The fact that methane is really not increasing is …an inconvenient truth.

The Oregon Graduate Institute has been involved in a project to accurately monitor methane concentrations worldwide for several decades, and the data for the Khalil et al. article come from “weekly flask sampling measurements taken at six strategically located sites, one in each of the polar, middle, and tropical latitudes of both hemispheres (Barrow, Alaska 71.16 N, 156.5 W; Cape Meares, Oregon 45.5 N, 124 W; Mauna Loa 21.08 N, 157.2; Wand Cape Kumukahi 19.3 N, 154.5 W, Hawaii; Samoa 14.1 S, 170.6 W; Cape Grim, Tasmania 42 S, 145 E; and Antarctica including Palmer Station 64.46 S, 64 W and the South Pole 90 S).” They used some statistical wizardry to produce a global average for every month, and the results are presented in Figure 1.

Figure 1. Global monthly methane concentration in parts per billion (ppb).

The research team writes “it is apparent that there are ups and downs, but these are superimposed on a systematically declining rate of accumulation. The slowdown of methane trends has been known and discussed for a long time; however, it is particularly noteworthy that the decrease of the methane trend is not a new phenomenon, but rather it has occurred from the time that systematic measurements were first taken. Most probably it started even before then. Since fluctuations are superimposed on a generally decreasing trend, there have been years in recent times when methane has not increased at all or has even fallen slightly relative to the previous year. This has attracted more interest than in the past when there were similar short-term down turns but on the whole methane still increased over previous years. The recent incursions of the trend into negative territory are therefore part of a much longer term process.”

In describing the implications of their work, they note “it is questionable whether human activities can cause methane concentrations to increase greatly in the future.” Simple and well put.


Khalil, M.A.K., C.L. Butenhoff, and R.A. Rasmussen, 2007. Atmospheric Methane: Trends and Cycles of Sources and Sinks. Environmental Science and Technology, available on-line (10.1021/es061791t).

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