For over 40 years (1961-2002), the Greenland ice sheet cooled, thickened, and gained mass just as anthropogenic CO2 emissions were sharply rising.
Image Source: Mikkelsen et al., 2018
According to Greenland ice sheet instrumental records, there was a dramatic cooling trend during summer months from the late 1980s to early 2000s (Chylek et al., 2004).
“The average temperature of the warmest month and the summer average (June, July and August) temperature show a decreasing trend of 3.0 and 2.2°C/decade between 1987 and 2001.”
Image Source: Chylek et al., 2004
Greenland had been gaining +40 Gt of ice per year during 1961-1990 (Fettweis et al., 2017).
Coincident with the cooling, the ice sheet was still thickening and gaining mass – +11 Gt (gigatons) per year – as recently as 1992-2002 (Zwally et al., 2005).
Annual anthropogenic CO2 emissions rates tripled during this 41-year period, and atmospheric CO2 rose by nearly 60 parts per million (317 ppm to 375 ppm).
Image(s) Source: Johannessen et al., 2005, Zwally et al., 2005, Fettweis et al., 2017
After 2002, the Greenland ice sheet began losing mass as the ice sheet temperatures warmed.
This warming and mass loss trend have often been attributed to the rise in CO2 emissions by those promoting anthropogenically-driven global warming (AGW).
But if rising CO2 emissions are the causal mechanism for the post-2002 warming and mass loss, why did the Greenland ice sheet cool and gain about 1.35 trillion metric tons of ice for the duration of 41 years as CO2 emissions rates tripled from ~2.5 GtC/yr (gigatons of carbon per year) to ~7.5 GtC/yr?
Succinctly, why would an ice sheet both lose and gain mass as CO2 rises?