|Fig. 1 Source: NOAA ESRL|
The sources of CH4 in the atmosphere are not as well known as the sources of CO2 are (Fig. 2), nor are the records as extensive for CH4 (Fig. 1).
The watchers at Moana Loa observatory, in Hawaii, keep records for both of those green house gases (GHG) and are considered to be a standard source of information (Moana Loa CO2).
|Fig. 2 Source NOAA|
Currently, scientists do not have a tool to say with certainty how much, or if any, atmospheric methane comes from hydrates.(The Methane Hydrate / Clathrate Controversy, quoting experts). The official keeper of GHG levels at Moana Loa indicates that it is a ho-hum compared to CO2:
No one can yet say with certainty how the methane release in the Arctic will develop with global warming, either in the ocean or on the land. This research is still in its infancy.
Methane was steadily increasing in the 1980's, it's growth rate slowed in the 1990's, and it has had a near-zero growth rate for the last few years.(NOAA ESRL). At this time competent researchers use inexact language in several categories:
"In this paper we present 2 years of data obtained during the late summer period (September 2003 and September 2004) for the East Siberian Arctic shelf (ESAS). According to our data, the surface layer of shelf water was supersaturated up to 2500% relative to the present average atmospheric methane content of 1.85 ppm, pointing to the rivers as a strong source of dissolved methane which comes from watersheds which are underlain with permafrost. Anomalously high concentrations (up to 154 nM or 4400% supersaturation) of dissolved methane in the bottom layer of shelf water at a few sites suggest that the bottom layer is somehow affected by near-bottom sources. The net flux of methane from this area of the East Siberian Arctic shelf can reach up to 13.7 × 104 g CH4 km− 2 from plume areas during the period of ice free water, and thus is in the upper range of the estimated global marine methane release. Ongoing environmental change might affect the methane marine cycle since significant changes in the thermal regime of bottom sediments within a few sites were registered. Correlation between calculated methane storage within the water column and both integrated salinity values (r = 0.61) and integrated values of dissolved inorganic carbon (DIC) (r = 0.62) suggest that higher concentrations of dissolved methane were mostly derived from the marine environment, likely due to in-situ production or release from decaying submarine gas hydrates deposits. The calculated late summer potential methane emissions tend to vary from year to year, reflecting most likely the effect of changing hydrological and meteorological conditions (temperature, wind) on the ESAS rather than riverine export of dissolved methane. We point out additional sources of methane in this region such as submarine taliks, ice complex retreat, submarine permafrost itself and decaying gas hydrates deposits."(Sharkova). Arctic methane research is increasing rapidly, so tools and methods should improve over time, so that more exact language can be used.
The research into this potentially dangerous area is not as mature, by any stretch of the imagination, as sea level change (SLC) research is.
Tidal gages have been used for over a hundred years, satellites of all sorts (e.g. GRACE, Cryosat-2, etc.) have measured the sources of sea level rise (SLR) and sea level fall (SLF), and they are well known without controversy.
Those who rant on about the "non-issue" of SLC but "the human species destroying methane danger" will be seen, and should be seen, as kooks by public infrastructure managers.
That is because SLC is a known clear and present danger (a must-read for that perspective: You Are Here - 5).
An expert on SLC addresses those issues (which are relatively hidden in plain sight) in one video below (Mitrovica), and an expert on Arctic methane release does the same in the other video (Sharkova).
The previous post in this series is here.