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Blockbuster: Planetary temperature controls CO2 levels — not humans

Posted By Joanne Nova On August 5, 2011 @ 12:46 am In Global Warming | Comments Disabled

There goes another “fingerprint”…

It’s not just that man-made emissions don’t control the climate, they don’t even control global CO2 levels.

Judging by the speech gave at the Sydney Institute, there’s a blockbuster paper coming soon.

Listen to the speech: “Global Emission of Carbon Dioxide: The Contribution from Natural Sources”

Professor Murry Salby is Chair of Climate Science at Macquarie University. He’s been a visiting professorships at Paris, Stockholm, Jerusalem, and Kyoto, and he’s spent time at the Bureau of Meterology in Australia.

Over the last two years he has been looking at C12 and C13 ratios and CO2 levels around the world, and has come to the conclusion that man-made emissions have only a small effect on global CO2 levels. It’s not just that man-made emissions don’t control the climate, they don’t even control global CO2 levels.

CO2 variations do not correlate with man-made emissions. Peaks and falls correlate with hot years (e.g. 1998) and cold years (1991-92). No graphs are available from Salby's speech or paper yet. This graph comes from Tom Quirk's related work (see below).

The higher levels of CO2 in recent decades appear to be mostly due to natural sources. He presented this research at the IUGG conference in Melbourne recently, causing great discussion and shocking a few people. Word reached the Sydney Institute, which rushed to arrange for him to speak, given the importance of this work in the current Australian political climate.

The ratio of C13 to C12 (two isotopes of carbon) in our atmosphere has been declining, which is usually viewed as a signature of man-made CO2 emissions. C12 makes up 99% of carbon in the atmosphere (nearly all atmospheric carbon is in the form of CO2). C13 is much rarer — about 1%. Plants don’t like the rarer C13 type as much; photosynthesis works best on the C12 -type -of-CO2 and not the C13-type when absorbing CO2 from the air.

Prof Salby points out that while fossil fuels are richer in C12 than the atmosphere, so too is plant life on Earth, and there isn’t a lot of difference (just 2.6%) in the ratios of C13 to C12 in plants versus fossil fuels. (Fossil fuels are, after all, made in theory from plants, so it’s not surprising that it’s hard to tell their “signatures” apart). So if the C13 to C12 ratio is falling (as more C12 rich carbon is put into the air by burning fossil fuels) then we can’t know if it’s due to man-made CO2 or natural CO2 from plants.

Essentially we can measure man-made emissions reasonably well, but we can’t measure the natural emissions and sequestrations of CO2 at all precisely — the error bars are huge. Humans emits 5Gt or so per annum, but the oceans emit about 90Gt and the land-plants about 60Gt, for a total of maybe 150Gt. Many scientists have assumed that the net flows of carbon to and from natural sinks and sources of CO2 cancel each other out, but there is no real data to confirm this and it’s just a convenient assumption. The problem is that even small fractional changes in natural emissions or sequestrations swamp the human emissions.

UPDATE Inserted: E.M.Smith covered this point well in 2009


“It is often asserted that we can measure the human contribution of CO2 to the air by looking at the ratio of C12 to C13. The theory is that plants absorb more C12 than C13 (by about 2%, not a big signature), so we can look at the air and know which came from plants and which came from volcanos and which came from fossil fuels, via us. Plants are ‘deficient’ in C13, and so, then, ought to be our fossil fuel derived CO2.

The implication is that since coal and oil were from plants, that “plant signature” means “human via fossil fuels”. But it just isn’t that simple. Take a look at the above chart. We are 5.5 and plants are putting 121.6 into the air each year (not counting ocean plants). There is a lot of carbon slopping back and forth between sinks and sources. Exactly how closely do we know the rate of soil evolution of CO2, for example?”

Chiefio also found some interesting quotes pointing out that corn (a C4 plant) absorbs more C13, and our mass fields of corn might just muck up the stats… (it’s a good post).

The sources of CO2 don’t seem to be industrialized areas

Suspiciously, when satellites record atmospheric CO2 levels around the globe they find that the sources don’t appear to be concentrated in the places we’d expect — industry or population concentrations like western Europe, the Ohio Valley, or China. Instead the sources appear to be in places like the Amazon Basin, southeast Asia, and tropical Africa — not so much the places with large human emissions of CO2!

But CO2 is a well mixed gas so it’s not possible to definitively sort out the sources or sinks with CO2 measurements around the globe. The differences are only of the order of 5%.

Instead the way to unravel the puzzle is to look at the one long recording we have (at Mauna Loa, in Hawaii, going back to 1959) and graph the changes in CO2 and in C13 from year to year. Some years from January to January there may be a rise of 0 ppmv (ie no change), some years up to 3 ppmv. If those changes were due to man-made CO2 then we should see more of those rapid increases in recent times as man-made emissions increased faster.

What Salby found though, was nothing like what was expected

The largest increases year-to-year occurred when the world warmed fastest due to El Nino conditions. The smallest increases correlated with volcanoes which pump dust up into the atmosphere and keep the world cooler for a while. In other words, temperature controls CO2 levels on a yearly time-scale, and according to Salby, man-made emissions have little effect.

The climate models assume that most of the rise in CO2 (from 280 ppmv in1780 to 392 ppmv today) was due to industrialization and fossil fuel use. But the globe has been warming during that period (in fact since the depths of the Little Ice Age around 1680), so warmer conditions could be the reason that CO2 has been rising.

Salby does not dispute that some of the rise in CO2 levels is due to man-made emissions, but found that temperature alone explains about 80% of the variation in CO2 levels.

The up and coming paper with all the graphs will be released in about six weeks. It has passed peer review, and sounds like it has been a long time coming. Salby says he sat on the results for six months wondering if there was any other interpretation he could arrive at, and then, when he invited scientists he trusted and admired to comment on the paper, they also sat on it for half a year. His speech created waves at the IUGG conference, and word is spreading.

A book will be released later this year: Physics of the Atmosphere and Climate.

Roy Spencer wrote along similar lines last year

Could the Ocean, Rather Than Mankind, Be the Reason?” and Part II


...In Fig. 5 we see that the yearly-average CO2 increase at Mauna Loa ends up being anywhere from 0% of the human source, to 130%. It seems to me that this is proof that natural net flux imbalances are at least as big as the human source. [Roy Spencer

“…   the human source represents only 3% (or less) the size of the natural fluxes in and out of the surface.  This means that we would need to know the natural upward and downward fluxes to much better than 3% to say that humans are responsible for the current upward trend in atmospheric CO2.  Are measurements of the global carbon fluxes much better than 3% in accuracy??  I doubt it.”

Roy Spencer

Tom Quirk in Australia has been asking these questions for years

Tom Quirk showed that while most man-made CO2 is released in the Northern Hemisphere, and the southern Hemisphere stations ought to take months to record the rises, instead there did not appear to be any lag… (ie. the major source of the CO2 is global rather than from human activity).

Over 95% of [man-made emissions of] CO2 has been released in the Northern Hemisphere…

“A tracer for CO2 transport from the Northern Hemisphere to the Southern Hemisphere was provided by 14C created by nuclear weapons testing in the 1950’s and 1960’s.The analysis of 14C in atmospheric CO2  showed that it took some years for exchanges of CO2 between the hemispheres before the 14C was uniformly distributed…

“If 75% of CO2 from fossil fuel is emitted north of latitude 30 then some time lag might be expected due to the sharp year-to-year variations in the estimated amounts left in the atmosphere. A simple model, following the example of the 14Cdata with a one year mixing time, would suggest a delay of 6 months for CO2 changes in concentration in the Northern Hemisphere to appear in the Southern Hemisphere.

“A correlation plot of …year on year differences of monthly measurements at Mauna Loa against those at the South Pole [shows]… the time difference is positive when the South Pole data leads the Mauna Loa data. Any negative bias (asymmetry in the plot) would indicate a delayed arrival of CO2 in the Southern Hemisphere.

“There does not appear to be any time difference between the hemispheres. This suggests that the annual increases [in atmospheric carbon dioxide] may be coming from a global or equatorial source.”

Tom has done  a lot of work on this:

The constancy of seasonal variations in CO2 and the lack of time delays between the hemispheres suggest that fossil fuel derived CO2 is almost totally absorbed locally in the year it is emitted. This implies that natural variability of the climate is the prime cause of increasing CO2, not the emissions of CO2 from the use of fossil fuels.

‘Sources and Sinks of Carbon Dioxide’, by Tom Quirk, Energy and Environment, Volume 20, pages 103-119.  http://www.multi-science.co.uk/ee.htm

More info from Tom Quirk: SOURCES AND SINKS OF CARBON DIOXIDE  [17 page PDF]

But what about the ice cores?

The Vostok ice core record suggests CO2 levels have not been this high in the last 800,000 years, but if Salby is right, and temperature controls CO2, then CO2 levels ought to have been higher say, 130,000 years ago when the world was 2 – 4 degrees warmer than it is now.

Salby questions the ice core proxy and points out that in the ice cores, as temperature rises, C13 falls, much as it has been in the last 50 years. If it was also responding that way hundreds of thousands of years ago, then the C13 to C12 ratio can hardly be called a fingerprint of human emissions.

On the nature of science

According to Salby, science is about discourse and questioning. He emphasized the importance of debate: “Excluding discourse is not science”. He felt that it was not his position to comment on policy, saying the scientists that do are more activist than scientist.

After speaking in carefully selected phrases, he  finished his presentation saying that “anyone who thinks the science is settled on this topic, is in fantasia”.

Salby was once an IPCC reviewer, and comments, damningly, that if these results had been available in 2007, “the IPCC could not have drawn the conclusion that it did.” I guess he’s also giving them an out.


Prof Murry Salby has worked at leading research institutions, including the US National Center for Atmospheric Research, Princeton University, and the University of Colorado, and is the author of Fundamentals of Atmospheric Physics, and Physics of the Atmosphere and Climate, due out in 2011. [Thanks to Andrew Bolt]

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