This is the difference in the atmospheric methane of a given year compared to the previous year. We call it an ‘increase’ because in recent history, most years have had more methane in the atmosphere than the previous year; however, several years have had a negative value, which means there was a decrease.
Methane has a large warming effect, considering its much higher Global Warming Potential (GWP) than CO2, but it only acts for a relatively brief period compared to CO2. Methane breaks down quickly in the atmosphere, and a reduction in emissions can cause a rapid decline in its levels and impact.
The yearly methane increase depends on the processes that emit methane into the atmosphere and on methane sinks, like atmospheric breakdown and soil reactions.Wikipedia: Atmospheric Methane
The primary unit here is parts per billion (ppb), which describes the increase in the concentration of atmospheric methane per year. The secondary unit here is a megatonne, which describes the weight of the increase of atmospheric methane per year. We show this to be able to relate to emissions, which are commonly expressed in megatonnes.Wikipedia: Parts-per notation
In the long term, there is an average yearly increase in atmospheric methane largely due to human emissions. There are still many uncertainties about the causes of the fluctuations. Since the 1980s there has been a reduction in the increase in atmospheric methane, and between 2000 and 2006 there was even a period of almost no increase. These reductions were partly due to the Mount Pinatubo volcanic eruption and the reduction of emissions in the oil and gas sectors. The high increase from 2014 to 2019 is thought to be partly due to prolonged El Niño conditions.
NOAA has reported a record increase in atmospheric methane during 2021: “For the second year in a row, NOAA scientists observed a record annual increase in atmospheric levels of methane, a powerful, heat-trapping greenhouse gas that’s the second biggest contributor to human-caused global warming after carbon dioxide.”NOAA News: Increase in atmospheric methane set another record during 2021
The data is from several sources linked to the National Oceanic and Atmospheric Administration (NOAA). National Centers for Environmental Information has data from ice core studies where we average the extrapolated yearly increases of the individual studies. That is used for the time period prior to 1984 and highlights the long term trend, but does not show actual yearly fluctuations. Since 1983 NOAA has measured methane at a globally distributed network of air sampling sites.
Global Monitoring Laboratory provides annual methane mole fraction increase (ppb) from Jan 1 through Dec 31. For the current year we compare the available months to those a year earlier.NOAA GML: Trends in Atmospheric Nitrous Oxide
Globally averaged marine surface annual mean growth rates dataCredits: Ed Dlugokencky, NOAA/GML (gml.noaa.gov/ccgg/trends/trends_ch4/)Update cycle: annualDelay: ~ 3 months
Globally averaged marine surface monthly mean dataCredits: Ed Dlugokencky, NOAA/GML (gml.noaa.gov/ccgg/trends/trends_ch4/)Update cycle: monthlyDelay: ~ 3 months
Law Dome Ice Core 2000-Year CO2, CH4, and N2O DataCredits: MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins. 2006. The Law Dome CO2, CH4 and N2O Ice Core Records Extended to 2000 years BP. Geophysical Research Letters, Vol. 33, No. 14, L14810 10.1029/2006GL026152.
ReferencesReference: Original references for Law Dome Ice Core 2000-Year CO2, CH4, and N2O Data
Reference: Law Dome CO2 and CH4 records of the last 1000 years first published in Etheridge et al., 1996 and 1998. Newer results which fill in gaps, extend record to 2000 BP and include N2O, were published and explained in detail in MacFarling Meure et al. 2006 and MacFarling Meure 2004. Some new CH4 results were also published in Ferretti et al. 2005.
Reference: Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M. Barnola, and V.I. Morgan. 1996. Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn. Journal of Geophysical Research, 101, 4115-4128.
Reference: Etheridge, D.M., L.P. Steele, R.J. Francey, and R.L. Langenfelds. 1998. Atmospheric methane between 1000 A.D. and present: evidence of anthropogenic emissions and climatic variability. Journal of Geophysical Research, 103, 15979-15996.
Reference: MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins. 2006. The Law Dome CO2, CH4 and N2O Ice Core Records Extended to 2000 years BP. Geophysical Research Letters, Vol. 33, No. 14, L14810 10.1029/2006GL026152.
Reference: MacFarling Meure, C. 2004. The natural and anthropogenic variations of carbon dioxide, methane and nitrous oxide during the Holocene from ice core analysis. PhD thesis, University of Melbourne.
Reference: Ferretti, D.F., J.B. Miller, J.W.C. White, D.M. Etheridge, K.R. Lassey, D.C. Lowe, C.M. MacFarling Meure, M.F. Dreier, C.M. Trudinger, and T.D. van Ommen. 2005. Unexpected Changes to the Global Methane Budget over the Last 2,000 Years. Science, 309 (5741): 1714-1717.