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David Middleton

The “residency time” of CO2 is on the order of 5-7 years, however that’s not really relevant. While humans are a relatively insignificant source of CO2 on an annual basis, we take carbon out of geologic sequestration and put back into the active carbon cycle. Little by little, we have increased the total “pool” of carbon in the cycle. There is a cumulative effect. It will take the Earth time to move that carbon back into geologic sequestration… Anywhere from 30 to 500 years… No one really knows for sure.

Regarding the “abnormality” of the modern atmospheric CO2 concentration (~400 ppm). Fossil plant stomata and Greenland ice cores clearly indicate that 300-350 ppm has not been unusual during the Holocene, with possible excursions to the 400 ppm vicinity. Apart from the DE08 ice core from Law Dome, all of the other Antarctic ice cores are incapable of resolving short-duration CO2 shifts, most have resolutions coarser than 100 years. If Law Dome was reduced to the resolution of the Vostok core, the modern rise in CO2 would not be resolved, and barely detectable.
This is a composite CO2 chronology from multiple Antarctic ice cores:

[Image: no-smooth.png]
-51-1800 yr BP:’

Law Dome (Rubino et al., 2013)

1.8-2 kyr BP:

Law Dome (MacFarling Meure et al., 2006)

2-11 kyr BP:

Dome C (Monnin et al., 2001 + 2004)

11-22 kyr BP:

WAIS (Marcott et al., 2014) minus 4 ppmv (see text)

22-40 kyr BP:

Siple Dome (Ahn et al., 2014)

40-60 kyr BP:

TALDICE (Bereiter et al., 2012)

60-115 kyr BP:

EDML (Bereiter et al., 2012)

105-155 kyr BP:

Dome C Sublimation (Schneider et al., 2013)

155-393 kyr BP:

Vostok (Petit et al., 1999)

393-611 kyr BP:

Dome C (Siegenthaler et al., 2005)

612-800 kyr BP:
Dome C (Bereiter et al., 2014)

These ice cores are of vastly different resolutions. Petit et al., 1999 indicate that the CO2 resolution for Vostok is 1,500 years. Lüthi et al., 2008 suggest a CO2 resolution of about 500 years for Dome C. The Hockey Stick blade (368 ppm spike) is from Law Dome DE08. It appears that the high resolution Law Dome DE08 core was just spliced on to the lower frequency older ice cores.

If I use a 500-yr smoothing filter (Dome C resolution), the Hockey Stick loses its blade completely:

[Image: 500-smooth.png]


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