AC Osborn
“Apples with apples” comparison between the statistically indistinguishable early 20thC and late 20thC warming cycles: 1910-1940 and 1970-2000, using HadCRUT4, Mauna Loa after 1958 and Siegenthaler et al. ice core data prior to 1958.
Linear dT
1910 to 1940 = 0.4C
1970 to 2000 = 0.5C
CO2
1910 = 299 ppmv
1940 = 309 ppmv
1970 = 324 ppmv
2000 = 369 ppmv
ASS-U-ME that IPCC estimate for 2xCO2 TCR of 1.8C is correct
Early 20thC cycle
ln (309 / 299) = 0.0329
ln (2) = 0.6931
dT from CO2 = 1.8 * 0.0329 / 0.6931 = 0.09C
dT from other causes = 0.4 – 0.09 = 0.31C
CO2 “caused” 21% of warming
Late 20thC cycle
ln (369 / 324) = 0.1301
dT from CO2 = 1.8 * 0.1301 / 0.6931 = 0.34C
dT from other causes = 0.5 – 0.34 = 0.16C
CO2 “caused” 68% of warming
Over both warming cycles CO2 “caused” 48% of the warming
If a lower estimate for 2xCO2 TCR of 1.0C is correct:
(Early 20thC cycle) dT from CO2 = 0.05C; dT from others = 0.35C
CO2 “caused” 12% of warming
(Late 20thC cycle) dT from CO2 = 0.19C; dT from others = 0.31C
CO2 “caused” 38% of warming
Over both warming cycles CO2 “caused” 27% of the warming
So it all depends on what you ASS-U-ME for 2xCO2 TCR.
Max