Guest essay by Rud Istvan
Dr. Murry Salby has been getting substantial attention in the climate blogosphere, for two reasons. First is his theory that at least 2/3 of the observed increase in atmospheric CO2 is natural and temperature induced. Second are the circumstances surrounding his departure from U. Colorado and later termination from Macquarie University. This post covers the first and not the second, and is motivated by a very recent WUWT post on the mysteries of OCO-2, where the Salby theory was raised yet again in comments.
Dr. Salby developed a substantial scientific reputation for work on upper atmosphere wave propagation and stratospheric ozone. He has published two textbooks, Atmospheric Physics (1996) and Physics of the Atmosphere and Climate (2012). His new theory that most of the increase in atmospheric CO2 is naturally temperature induced (NOT anthropogenic) is not published. He explicated it in a Hamburg lecture 18 April 2013, and a London lecture 17 March 2015. Both are available on YouTube. (Search his name to find, view, and critique them before reading on if you want to deep dive.) This post does not reproduce or critique his arguments in detail. (There are fundamental definitional, mathematical, and factual observation errors. Perhaps a more detailed companion post will follow detailing them with footnotes if this does not suffice.) This post only addresses whether his conclusions are supported by observations; it is a macro Feynman test rather than a Salby details deep dive.
Controversial CO2 Atmospheric Concentration Theory
The core of Salby’s theory is derived using CO2 data from MLO’s Keeling Curve since 1958, and satellite temperature data since 1979. (His few charts reaching back to 1880 contain acknowledged large uncertainties.) His theory builds off a simple observation, that in ‘official’ estimates of Earth’s carbon cycle budget, anthropogenic CO2 is only a small source compared to large natural sources and sinks. This is illustrated by IPCC AR4 WG1 figure 7.3.
He then deduces there must be rapidly responding temperature dependent natural CO2 net sources much greater than anthropogenic sources. This is a very questionable argument on short decadal time frames. Gore got it wrong, and Salby got it wrong. The ice core based CO2 lagged change to temperature is about 800 years, common sensically corresponding to the thermohaline circulation period. (For rigorous calculations on Salby’s decadal time scales using residency half-lives and efold times, see Eschenbach’s post at http://www.wattsupwiththat.com/2015/04/19/the-secret-life-of-half-life/
He observationally bolsters his conclusion by ‘showing’ that highest CO2 concentrations are over relatively uninhabited/unindustrialized regions like the Amazon basin, so must have natural origins. The following ‘observational’ figure is from his Hamburg lecture. Except it is completely disproved by OCO-2.
As Feynman said, observation trumps theory.
First, if Salby is right, the rise in atmospheric CO2 concentrations should have slowed or stopped because of the ‘pause’. They haven’t. They bear no short or long term relationship to one another. Since 2000, CO2 has increased about 35% on the 1958 Keeling curve base; temperatures haven’t (the pause). The seasonality of the northern hemisphere terrestrial photosynthetic sink is apparent in the Keeling curve, as is the temperature/CO2 discrepancy disproving Salby.
Second, satellites have NOT generally observed higher CO2 concentrations over uninhabited/ unindustrialized regions in past two decades. (The following NASA charts use AIRS IR sensors on various satellites to estimate gridded CO2 concentrations from peak CO2 OLR absorption wavelengths. The new OCO-2 data is even more stark.)
Third, Salby’s theory requires that land and/or sea serve as the temperature dependent CO2 net sources that ‘overwhelm’ anthropogenic CO2 emissions from fossil fuels and cement production. That is NOT true either; both land and sea have been serving as net sinks.
Terrestrial biomass (net primary productivity, NPP) is an increasing sink. This has been observed in multiple ways, including NASA AVHRR (1982-2009) and MODIS (2000-2009) ‘normalized difference vegetative index’ (NDVI). NDVI has been ground truthed by sampling NPP including both ‘roots and shoots’ by ecosystem. The terrestrial net biological sink has increased since 1980. It is not a source. The most recent paper is NASA’s 14% greening in 30 years, published 4/16/2016 and previously remarked at WUWT.
That leaves oceans. Biologically, oceans are a net carbon sink through photosynthesis and calcification. Satellites detect this through planktonic chlorophyll concentrations.
But there are certainly large ocean zones that are relatively barren (mainly from lack of iron fertilization in the form of dust). Those large blue barren swaths are where ocean water pCO2 and pH are monitored, precisely to minimize confounding biological sink influences recently explained on WUWT by Dr. Jim Steele. Could those also be a net source?
Barren ocean regions are mainly influenced Henry’s Law and Le Chatellier’s Principle. The first says partial pressures of ocean dissolved CO2 and atmospheric CO2 will equilibrate. The second partly says colder water stores more dissolved CO2. ARGO suggests the oceans are warming. Could Le Chatellier be stronger than Henry, in which case oceans could provide Salby’s requisite rapidly temperature dependent net natural source? There are two stations, Aloha 100 km north of Oahu (maintained by University of Hawaii and WHOI) and BATS off Bermuda (maintained by WHOI) where the hypothesis can be tested by observations. Both show even barren oceans are a net carbon sink since 1980. Barren ocean pH declines as pCO2 increases.
If there are no observational temperature dependent natural CO2 sources, and temperature dependent sinks (NH temperate terrestrial vegetation) increase with temperature, then Salby’s natural carbon dioxide theory cannot be true. It is falsified. Even before detailing his definitional, mathematical, and factual errors.