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The Great Channel 4 Swindle. Robin Hogan Thanks to: Jonathan Gregory, Giles Harrison and Peter Stott. Return. Overview. The following claims were made in “The Great Global Warming Swindle” produced by Martin Durkin: “Concentrations of CO 2 are too small to be important”

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the great channel 4 swindle

The Great Channel 4 Swindle

Robin Hogan

Thanks to: Jonathan Gregory, Giles Harrison and Peter Stott


  • The following claims were made in “The Great Global Warming Swindle” produced by Martin Durkin:
    • “Concentrations of CO2 are too small to be important”
    • “CO2 doesn’t match 20th century temperature record”
    • “It can all be explained by sunspots”
    • “The troposphere isn’t warming”
    • “Volcanoes emit far more CO2 than humans”
concs of co 2 300ppmv are too small
“Concs of CO2 (~300ppmv) are too small”
  • But the “per-molecule” absorption cross-section of CO2 is hugely greater than N2 and O2 in the infrared

Carbon dioxide absorption in the middle of the infrared spectrum

…a daft comment anyway: 300 ppmv of HCN is lethal, so why shouldn’t 300 ppmv of CO2 be important?

whoever said only co 2 affects climate
Whoever said only CO2 affects climate?

Anthropogenic forcings

Carbon dioxide and other gases

Tropospheric aerosol emissions

Land use changes

Natural forcings with an established mechanism

Stratospheric aerosol (volcanoes)

Solar irradiance changes

Changes to Earth’s orbit (Milankovic cycles) (~20 kyr)

Solar cycle effect on ozone via UV modulation (11 yr)

Possible natural forcings lacking an established mechanism

Cosmic ray effects on clouds (11 or 22 yr?)

Solar system and galactic spiral arms (~0.5 Gyr)

And natural variability!




Official NASA data have an earlier upturn

from the independent
From The Independent
  • Source of Channel 4 temperature plot
    • 1998 article in “Medical Sentinel” by known climate sceptics
    • From NASA but “Northern hemisphere land” (<1/3 of globe)
    • Ended in the early-1980s so underplayed recent warming
    • Martin Durkin admitted that his graphics team changed the scale so that it extended to 2000!
  • Durkin quotes on the matter
    • “there was fluff there”
    • “the original Nasa data was very wiggly-lined and we wanted the simplest line we could find”
Shape of temperature rise can be calculated by considering natural and anthropogenic forcings
  • “Post-war economic boom” led to aerosol emissions, initially offsetting the CO2 forcing



Pinatubo 1991

El Chichon


more recently ipcc 2007
More recently: IPCC 2007

Solar irradiance + volcanoes

Carbon dioxide + aerosols


friis christensen lassen 1991
Friis-Christensen & Lassen (1991)

Smoothed solar-cycle length

Un-smoothed points (end of time series as of 1991)

When the new data became available: Lassen and Friis-Christensen 2000

Corrected by Damon and Laut (2004)

Solar cycle length clearly cannot explain the last 50 years of warming
  • But discredited data still used in C4 programme!
  • Note that we can predict temperature change due to CO2, but cosmic ray link is currently just a correlation: mechanism is uncertain

Upturn previously used to explain recent warming now looks like a blip!

Damon and Laut (2004)

longer periods
?Longer periods…
  • Problems with fitting:
    • Maunder minimum “filled in” with perfectly correlated data
    • Two temperature series were “spliced together” at 1870, but lowering the second by 0.1 degrees!
    • The result looks less convincing when these effects are corrected
but lots of temperatures to chose from
But lots of temperatures to chose from!
  • Note that changes to the solar irradiance are important at certain times (e.g. beginning of 20th century), but these are correlated to sunspot number so we must be very careful in attribution of correlations of temperature with solar activity
  • Key point: no change in solar activity has been observed that could explain the warming in the last few decades
troposphere should warm faster than surface
“Troposphere should warm faster than surface”
  • This is consistent with recent analysis of satellite Microwave Sounding Unit (MSU)

Christy and Spencer (2003) analysis indicated troposphere warming slower than surface

Mears and Wentz corrected for diurnal drift of satellite: there is now consistency with theory

ipcc verdict
IPCC verdict
  • IPCC 2007:
    • “New analyses of balloon-borne and satellite measurements of lower- and mid-tropospheric temperature show warming rates that are similar to those of the surface temperature record and are consistent within their respective uncertainties, largely reconciling a discrepancy noted in the TAR*.”

*TAR = Third Assessment Report, IPCC 2001

volcanoes emit more co 2 than humans
Pinatubo 1991

Agung 1963

El Chichon 1982

“Volcanoes emit more CO2 than humans”
  • Steady outgassing: up to 0.2 GtC/yr (Morner and Etiope 2002), but IPCC 2001 has < 0.1 (cf. anthropogenic: 6 GtC/yr)
  • How much is emitted in a volcanic eruption?


Mauna Loa is itself a volcano!

useful links
Useful links


John Houghton’s site

The Independent

Point-by-point rebuttal

The graphs from the programme