The atmospheric build-up of methane—a major contributor the greenhouse effect—has slowed greatly. If current trends continue, it may reach zero within a few decades.
These findings appear in a remarkable new study by the National Oceanic and Atmospheric Administration (NOAA). Already, they have changed what we know about our global future.
But did this news make worldwide headlines or network broadcasts? Hardly. In fact, you’re probably hearing it here for the first time.
Though it appears in Nature magazine, this significant finding was missed (or more likely, ignored) by the major wire services. Their silence speaks volumes about the slanted coverage of global climate change issues.
Reducing the forecast
If this study is correct, we can reduce by 10 percent the current forecasts of future temperature increases resulting from human influences on the greenhouse.
This 10 percent reduction is equivalent to about two-thirds of the temperature savings that would result by the year 2050 if the whole world were to meet the emission requirements the United States agreed to under the Kyoto Protocol—all without costing a dime!
To date, increases in atmospheric methane concentrations have contributed an estimated 20 percent to the anthropogenic greenhouse effect. As with most greenhouse gases, methane levels have been increasing for more than a century. Anthropogenic sources of the odoriferous methane include landfills, coal mines, oil and natural gas, swamps and wetlands, and bovine flatulence and manure.
Moving toward equilibrium
Inexplicably, in 1992, the typical long-term methane growth rate of about 12 parts per billion (ppb) per year dropped to zero! At that time, scientists had many explanations for this "anomaly"—effects of dust from Mt. Pinatubo, declines in fossil fuel emission and tropical biomass burning, and drops in natural gas production (and methane leakage from pipes) in Russia, among others. Now, six years after Mt. Pinatubo blew its stack and at least three to four years after its atmospheric effects have disappeared, the methane growth rate remains suppressed.
The lead NOAA researcher, Ed Dlugokencky, no longer views this downturn as an anomaly. He suggests in the Nature article that atmospheric methane levels might soon stabilize.
Dlugokencky proposes that methane, which has an average lifetime of less than one decade, may be approaching global chemical equilibrium. This means that the amount of methane being removed from the atmosphere (by chemical reactions) is the same as the amount being added to it (by emissions). The emissions have become relatively constant, while the removal processes have been increasing. The two are expected to be in balance within a couple of decades. Thereafter, the atmospheric methane concentration will remain constant.
This finding could have a large impact on future climate change scenarios because, next to carbon dioxide, methane is the most important anthropogenic greenhouse gas in terms of its contribution to global temperature increases.
Behind the times
Contrast Dlugokencky’s findings with the projections used by the Inter-governmental Panel on Climate Change (IPCC) in their 1995 report. The IPCC, which is said to represent the "consensus of scientists," forecast that methane levels would more than double from the year 1990 to 2100! Dlugokencky’s new finding makes these forecasts seem ridiculous (Figure 1).
Figure 1. The IPCC projects methane concentration will double between now and 2100. But a new study shows methane is likely to level off at a concentration near today's level.
Instead of a projected methane concentration of 3,616 ppb by the year 2100 using the IPCC’s favorite emissions scenario, Dlugokencky suggests that the concentration may level out at about 1,800 ppb—a value of about half the IPCC projection.
Faced with these results, National Center for Atmospheric Research scientist David Schimel—the lead author of the IPCC chapter dealing with future methane concentrations—admitted that the assumptions about methane they were using when preparing the 1995 IPCC report were "based on an understanding of methane that was five to 15 years old." This is a remarkable statement—one that shows the inherent danger in producing science by consensus.
With the publication of one paper, the consensus is toppled.
Over the top
How much have the future scenarios of warming been overestimated because their proponents relied on outdated knowledge? Well, the IPCC projects that, by the year 2100, using their "best guess" emission scenario, the planet’s temperature will be about 2°C warmer than it was in 1990. This warming is supposed to be caused by an anthropogenic increase of effective carbon dioxide concentration (carbon dioxide plus all the other greenhouse gases) that produces an increase in the energy reaching the earth’s surface of 5 Watts per square meter (W/m2). The amount of this increase due to methane was forecast to be about 0.6W/m2 or 12 percent.
What the future holds—or doesn’t
If the methane concentration reaches equilibrium in the near future, methane’s contribution to the increase of energy will be negligible, and the total warming by the year 2100, according to the IPCC, should be only about 1.75°C. As we have discussed before (WCR, Vol. 2, No. 19), new climate models, the results of which were released after the IPCC 1995 report but which still use emission scenarios not incorporating the new methane results, suggest that the warming by the year 2100 will be more in the neighborhood of 1.5°C. Reducing these results by 10 percent nets you only 1.35°C—an amount that may not be far from the "who cares" level.
These results are still being viewed with caution because of the complex issues involved in their determination.
But atmospheric methane expert and IPCC contributor Inez Fung of the University of Victoria in British Columbia says these new findings represent "spectacular data," and that if the current trends hold up for another 10 years, she "would be ecstatic."
Even Schimel calls the findings "definitely good news." How quickly the consensus changes.
References:
Dlugokencky, E.J., et al., 1998, Continuing decline in the growth rate of the atmospheric methane burden. Nature, 393, 447–450.
Houghton, J.T., et al. (eds.), 1996, Climate Change 1995:
The Science of Climate Change. Intergovernmental Panel on Climate Change, Cambridge University Press, 572pp.