I've been looking into so-called smoking gun of greenhouse gas absorption: Harries et al 2001, and came across a rather hard to obtain, obscure 2003 follow-up paper by Harries co-authored with Brindley that basically nullifies the 2001 finding.
The paper is called Observations of the Infrared Outgoing Spectrum of the Earth from Space: The Effects of Temporal and Spatial Sampling by Brindley and Harries (hereafter B & H 2003).
Turns out sampling limitations (etc) in the later 1997 IMG instrument gave rise to errors that effectively nullify the following graph (as depicted on the SkS website):
|screenshot taken 27 Nov 2015|
In the 2001 Harries paper it is claimed that greenhouse gas heat-trapping was observed. But B & H 2003 shows that the difference is likely from other factors, such as water vapour, clouds, spatial and temporal variations in earth's spectrum of emission, and the aforementioned sampling errors.
Hence the desirability for "clear sky" measurements.
A huge admission is made in B & H 2003 that the May and June portions of the April-Jun sample period of Harries 2001 are compromised by clouds. Only the April data have a clear enough sky to be considered valid.
B & H 2003 investigates these issues which were not properly investigated in Harries 2001.
The measurement period for the Harries 2001 paper included all three months of April, May and June. But the April-only clear-sky measurements tell a very different story from Harries 2001.
It shows that between 1970 IRIS and 1997 IMG, despite atmospheric CO2 rising 37ppm during that time, CO2 has basically had no heat-trapping effect:
|Figure 9a from B & H 2003. IMG 1997 (dark line) IRIS 1970 (light line)|
|Figure 10a from B & H 2003. April 1997 spectrum minus April 1970 spectrum, as measured by two different satellites over a patch of Pacific Ocean (roughly 150W to 180W by 10S to 10N). Dotted lines are error bars from sampling (0.3K)|
There's supposed to be a much deeper absorption (a more negative value) near wavenumber 700 right at the left of the graph. But it's hardly below the line at all. The smoking gun's more like a smoking pea shooter:
If anything the foregoing disproves the CO2 heat-trapping theory.
Team Consensus loves to hide graphs like these B & H 2003 ones in a filing cabinet in a disused lavatory with a sign of "beware of the leopard" on the door...in other words they don't want you to see it because it ruins their narrative.
Professor Emeritus John E. Harries is a staunch member of Team Consensus [1, 2]. Perhaps that's why he so carefully worded his 2003 paper; very careful not to let on how devastating to the case of the 2001 paper it was. So much so that as late as the IPCC's 2007 AR4 still regarded it as significant.
But by the 2013 AR5, all mention of all Harries' spectral analysis papers quietly faded away from the IPCC publication, as they should. For the smoking gun had become more like a broken pea shooter.
Update: 28 Nov 2015: The B & H 2003 conclusion states:
The ﬁndings suggest that the sampling of IMG in particular is too coarse to provide an accurate representation of the atmospheric state....
...The question as to whether such a change could be considered to be representative of a climatic response to a given forcing, or was itself a natural ﬂuctuation, would require further detailed analysis.
And in that last paragraph is the real problem. We have no way of knowing whether the change Earth's emission spectrum is due to trace gases like CO2 or due to natural changes, which can produce similar spectral effects to CO2.
So you can't get a smoking gun of greenhouse gas absorption via these methods because CO2 can't be separated from water vapour & other greenhouse gases as well as other natural effects.
No wonder the excitement for Harries has fizzled since the initial buzz around 2001.
If they really had a smoking gun don't you think NASA etc would be heralding it from the roof-tops? Of course they would. But they keep their mouth shut because they know there is no smoking gun of change in earth's emission spectrum.
Update 21 Jun 2016: CO2 rose about 37 ppm in that time as seen here:
Here are all six relevant Harries papers. All five papers subsequent to the 2001 one in my opinion either invalidate or throw serious doubt on the 2001 result.
Harries et al 2001
Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997
Harries Brindley 2003
Observations of the Infrared Outgoing Spectrum of the Earth from Space: The Effects of Temporal and Spatial Sampling
Griggs, J. A., & Harries, J. E. (2004)
Comparison of spectrally resolved outgoing longwave data between 1970 and present.
Griggs, J. A., & Harries, J. E. (2005)
Comparison of spectrally resolved outgoing longwave radiation between 1970 and 2003: The ν4 band of methane
Griggs, Harries 2007
Comparison of Spectrally Resolved Outgoing Longwave Radiation over the Tropical Pacific between 1970 and 2003 Using IRIS, IMG, and AIRS
Chen, Harries et al 2007
Spectral signatures of climate change in the Earth’s infrared
spectrum between 1970 and 2006