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Does global warming lag or lead a rise in greenhouse gas concentration? (Rev #9)

Contents

Does global warming lag or lead a rise in greenhouse gas concentration? refers to a comparision of earth temperatures to concentrations of Green house gases (GHG). This page documents a discussion about the corresponding findings.

Discussion

In a comment in the Azimuth Forum John Baez mentioned the article:

• Ole Humlum, Kjell Stordahl, Jan-Erik Solheim, The phase relation between atmospheric carbon dioxide and global temperature, Global and Planetary Change 100 (2013), 51–69, http://www.sciencedirect.com/science/article/pii/S0921818112001658.

which claims to show temperature changes precede changes in carbon dioxide concentration.

The article has a response on the blog realclimate:

El Nino’s effect on CO2 causes confusion about CO2′s role for climate change — rasmus @ 11 September 2012

which critizeses the findings.

Charts

The article by Ole Humluma et al. provides the following chart

humlum co2 temperature phase

which was sort of reproduced by realclimate:

realclimateimage

Where Diff12 seems to be defined as the forward difference of two time dependend values differing by a year (here the values are the annual means of CO2 and temperature anomalies).

The US based “National climatic data center NOAA” provides the following chart in this context:

Temperature change and carbon dioxide change

NOAA chart temperature vs co2

which displays that co2 concentrations are sometimes lagging behind and sometimes precede temperature changes.

The data is here however not directly measured (since the data goes back to 450 000 ys), which may explain why the the “lagging behind” or “preceding” looks as being sometimes in the range of 10000-30000 years.

In this context it was pointed out that it would also be interesting to see charts of other green house gases vs. temperature. In particular the co2 concentration seems to be connected with the methane concentrations. On the wikipedia page: Atmospheric methane it was pointed out (23.02.2013) that:

Methane is created near the Earth’s surface, primarily by microorganisms by the process of methanogenesis. It is carried into the stratosphere by rising air in the tropics. Uncontrolled build-up of methane in the atmosphere is naturally checked — although human influence can upset this natural regulation — by methane’s reaction with hydroxyl radicals formed from singlet oxygen atoms and with water vapor. It has a net lifetime of about 10 years, (39) and is primarily removed by conversion to carbon dioxide and water.

where the reference (39) is:

see also Lifetime of Methane in the atmossphere in the Azimuth project.

Over half of the methane seems to be converted into co2, citation from p. 3 of Boucher et al:

This gives a lower bound of 0.51… and an upper bound of 1.0 for the fraction of methane that is converted to carbon dioxide.

However these findings are sofar somewhat in contradiction with information from other sources.

Methane and temperature

Following the above discussion about the decay of methane into CO2 I wanted to investigate the diff12 values of methane in comparision with temperature CO2. Unfortunately there is not much so much fine grain methane data available. In fact I found sofar only usable data from NOAA. In an email Ed Dlugokencky who has been in charge for the methane measurements at NOAA Mauna Loa pointed out that besides the systematic measurements of CH4 at the global scale from NOAA which started in 1983 there are measurements from UC Irvine, but which are infrequent and random spatial coverage (Blake et al.) and there is data from ice cores, firn air, and archive samples from Etheridge et al., 1998 JGR).

The diff12 of methane values can be compared in an interactive diagram at our personal website with the diff12 values of CO2 and Temperature anomalies from HADCRUT. The findings of Humlum et al. are recovered. Moreover it looks to me that methane diff12 values precede temperature diff12 values (and thus diff12 CO2 values, which could be due to the decay of methane into CO2). That is I find it looks indeed a bit as if most of the temperature diff12 peaks lag behind the methane peaks by approximately 1/2-1 a year 1). It would be good to compare this also with other temperature data, in particular with raw local temperatures and other locations. And apart from the fact that there might be a bug in the code - it is of course scientifically rather shaky to infer causal relations from such findings and thus it would be way too unsolid to infer from the above that methane might be a bigger driving force of global warming than CO2 - however it is suggestive to look for further evidence into that direction.

1)update 06122013: There was actually a bug (!) in the offsets in the drawing routines in the interactive applet which had been corrected by now. The lag doesn’t look anymore that big, but it still looks like there is a lag. Furthermore the new methane measurements are now included they go now until 12,2012.

Here a current screenshot of the interactive applet, where the red bar had been placed onto the most distinct peak for comparision:

screenshotApplet

Further discussions about this topic can be found at the Forum thread Temperature vs GHG concentrations and methane. In particular the role of precipitation and wetlands for cooling and methane emissions has been raised there.