Summary: Methane is a powerful greenhouse gas, and a favorite hobbyhorse of alarmists. It’s also an example of how they’ve abandoned the IPCC — the “gold standard” of climate science consensus. The IPCC’s most recent report, AR5’s Working Group I, is quite clear that methane levels in the atmosphere have grown more slowly than projected by their models — and that the risk posed by methane is real but not yet extreme. This is a follow-up to Some good news about our changing climate. Enjoy it, for it might not last long.
The report of Working Group I of the IPCC’s AR5 is quite explicit about the risk of methane emissions.
- Models’ projections of the growth in methane levels range from small to large.
- These projections have come down in each IPCC report.
- Methane levels have increased more slowly than in any of their projections.
You can read a hundred alarmist articles about methane and global warming — and never see this information from the IPCC.
Such complex stories are typical of many key questions about climate change (it’s science, not accounting), which is why we need the IPCC to put these things in a context understandable by laypeople. It’s not that the consensus is always right (it’s not), but rather that the science is not settled.
Let’s start with figure 1.6 from Chapter 1. This shows methane levels in the atmosphere in parts per billion (i.e., very small amounts), over time — compared with several generations of models’ projections.
Observed globally and annually averaged CH 4 concentrations in parts per billion (ppb) since 1950 compared with projections from the previous IPCC assessments. Estimated observed global annual CH4 concentrations are shown in dark blue. The shading shows the largest model projected range of global annual CH4 concentrations from 1950 to 2035 from FAR ( IPCC, 1990); SAR (1996); TAR (IPCC, 2001); and from AR4 (2007). The bars at the right-hand side of the graph show the full range given for 2035 for each assessment report.
The full story is told in Chapter 2 (citations omitted; red emphasis added):
Globally averaged CH4 in 1750 was 722 ± 25 ppb (after correction to the NOAA-2004 CH4 standard scale), although human influences on the global CH4 budget may have begun thousands of years earlier than this time that is normally considered ‘pre-industrial’.
In 2011, the global annual mean was 1803 ± 2 ppb. Direct atmospheric measurements of CH4 of sufficient spatial coverage to calculate global annual means began in 1978 and are plotted through 2011 in Figure 2.2a.
This time period is characterized by a decreasing growth rate (Figure 2.2b) from the early 1980s until 1998, stabilization from 1999 to 2006, and an increasing atmospheric burden from 2007 to 2011. Assuming no long-term trend in hydroxyl radical (OH) concentration, the observed decrease in CH4 growth rate from the early 1980s through 2006 indicates an approach to steady state where total global emissions have been approximately constant at ~550 Tg (CH4) yr–1.
Superimposed on the long-term pattern is significant interannual variability; studies of this variability are used to improve understanding of the global CH4 budget (Chapter 6). The most likely drivers of increased atmospheric CH4 were anomalously high temperatures in the Arctic in 2007 and greater than average precipitation in the tropics during 2007 and 2008.
Observations of the difference in CH4 between zonal averages for northern and southern polar regions (53° to 90°) suggest that, so far, it is unlikely that there has been a permanent measureable increase in Arctic CH4 emissions from wetlands and shallow sub-sea CH4 clathrates.
For More Information
(a) Reference Pages about climate on the FM sites:
- My posts
- Important things to know about climate change
- Studies & reports, by subject
- The history of climate fears
(b) Posts about the IPCC and climate change:
- “Climate Change: what do we know about the IPCC?”, 27 June 2010
- Hidden history about Madrid 1995: a look at the conference that changed the world, 11 September 2012 — About the writing of AR2
- The IPCC gets better. Climate alarmists freak-out., 19 December 2012
- The IPCC gives us straight talk about Extreme Weather, 4 October 2013
- The IPCC rebukes the climate doomsters. Will we listen?, 15 October 2013
- A summary of the state of climate change and extreme weather, 12 December 2013
- The IPCC releases its advice on “Impacts, Adaptation and Vulnerability”. To be attacked from both sides., 31 March 2014