From: DOE/LAWRENCE BERKELEY NATIONAL LABORATORY
First direct observations of methane’s increasing greenhouse effect at the Earth’s surface
Scientists have directly measured the increasing greenhouse effect of methane at the Earth’s surface for the first time. A research team from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) tracked a rise in the warming effect of methane – one of the most important greenhouse gases for the Earth’s atmosphere – over a 10-year period at a DOE field observation site in northern Oklahoma.
These findings were published online April 2 in the journal Nature Geoscience in an article entitled “Observationally derived rise in methane surface forcing mediated by water vapour trends.” The paper indicates that the greenhouse effect from methane tracked the global pause in methane concentrations in the early 2000s and began to rise at the same time that the concentrations began to rise in 2007.
“We have long suspected from laboratory measurements, theory, and models that methane is an important greenhouse gas,” said Berkeley Lab Research Scientist Dan Feldman, the study’s lead author. “Our work directly measures how increasing concentrations of methane are leading to an increasing greenhouse effect in the Earth’s atmosphere.”
Gases that trap heat in the atmosphere are called greenhouse gases, in large part because they absorb certain wavelengths of energy emitted by the Earth. As their atmospheric concentrations change, the scientific community expects the amount of energy absorbed by these gases to change accordingly, but prior to this study, that expectation for methane had not been confirmed outside of the laboratory.
The scientists analyzed highly calibrated long-term measurements to isolate the changing greenhouse effect of methane. They did this by looking at measurements over the wavelengths at which methane is known to exert its greenhouse effect and coupled those with a suite of other atmospheric measurements to control for other confounding factors, including water vapor.
This study was enabled by the comprehensive measurements of the Earth’s atmosphere that the DOE has routinely collected for decades at its Atmospheric Radiation Measurement (ARM) facilities, and conversely, would not be possible without such detailed observations.
The DOE ARM program manages and supports three long-term atmospheric observatories – the Southern Great Plains observatory in Oklahoma, the North Slope of Alaska observatory in far-northern Alaska, and the Eastern North Atlantic observatory on the Azores Islands. The program also deploys three ARM mobile facilities and several ARM aerial facilities. Together, these assets enable scientists to perform highly-detailed, targeted investigations to advance the fundamental scientific understanding of the Earth system.
The researchers believe this type of direct field observation can provide a more accurate and complete picture of the relationship between atmospheric greenhouse gas concentrations and their warming effect on Earth’s surface.
The research was funded by the Department of Energy’s Office of Science.
Here is the paper, unfortunately, even though it is funded by tax dollars, it is paywalled, which I consider an abuse of the public trust.
Observationally derived rise in methane surface forcing mediated by water vapour trends
Atmospheric methane (CH4) mixing ratios exhibited a plateau between 1995 and 2006 and have subsequently been increasing. While there are a number of competing explanations for the temporal evolution of this greenhouse gas, these prominent features in the temporal trajectory of atmospheric CH4 are expected to perturb the surface energy balance through radiative forcing, largely due to the infrared radiative absorption features of CH4. However, to date this has been determined strictly through radiative transfer calculations. Here, we present a quantified observation of the time series of clear-sky radiative forcing by CH4 at the surface from 2002 to 2012 at a single site derived from spectroscopic measurements along with line-by-line calculations using ancillary data. There was no significant trend in CH4 forcing between 2002 and 2006, but since then, the trend in forcing was 0.026 ± 0.006 (99.7% CI) W m2 yr−1. The seasonal-cycle amplitude and secular trends in observed forcing are influenced by a corresponding seasonal cycle and trend in atmospheric CH4. However, we find that we must account for the overlapping absorption effects of atmospheric water vapour (H2O) and CH4 to explain the observations fully. Thus, the determination of CH4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH4 and the vertically resolved trends in H2O.
Since the paper is pay-walled, I can’t check the veracity of the claims. but just reading over the press release, and looking at the photo and graph, I can make these observations.
- It’s one point on the globe, one measurement site. All they are doing is saying “this site, using a different measurement method, matches data gathered elsewhere”. Is that significant? Probably not.
- They mention two other ARM sites, but don’t provide data for the other two. Why?
- The photo provided looks like pasture land. How do they know what they’ve measured is representative of global trend, and not a local trend due to land use change, or increase in the number of cows?
- There’s a lot of oil and gas wells in Oklahoma, and fracking has been on the rise, perhaps that accounts for some of the increase in CH4.
- They don’t mention that methane has a short residence time in the atmosphere. The atmospheric residence time of methane is approximately 8 years . They leave the reader to think is is a permanent increase.
- The forcing went down slightly from 2002 to 2007 and then rose from 2007 to 2012. Nobody seems to be able to explain why it went down from 2002 to 2007.
- The study ends in 2012 – with just 10 years of data. Why? They don’t make that clear. Did the data start going down? Did the data source disappear?
- The graph below offers a reason for the increase from 2007 to 2012. It has data to 2015, and projections beyond.
From my viewpoint, the study raises more questions than it answers. However, based on the EIA graph above, we’ll probably hear a lot of caterwauling about methane and greenhouse effects in the future.
UPDATE: Reader Lance Wallace has made the paper and the supplemental data available
Full paper here. Also the Supporting Info with data sources