Annual carbon dioxide (CO2) and methane (CH4) change rates lag behind changes in sea ice extent by 7 months and 5 months, respectively. This robust correlation is consistent with the conclusion that CO2 (and CH4) changes are responsive to temperature, not the other way around.
It is commonly believed that the annual “squiggle” of the Mauna Loa CO2 cycle variations are driven by hemispheric seasonal contrasts in terrestrial photosynthesis.
But scientists (Hambler and Henderson, 2022) instead find it is variation high latitude temperatures affecting sea ice extent changes that dominate as drivers of the CO2 (and methane) annual fluxes, not photosynthesis.
They affirm temperature (T) changes lead CO2 change rates by about 7-10 months, suggesting the causality direction is T→CO2, and not CO2→T.
Temperature also drives sea ice peak melt vs. accumulation rates. This cause-effect directionality can also be clearly seen in analyses of sea ice flux vs. annual CO2 rate changes.
“The phase relationship between temperature and carbon dioxide has been examined to help elucidate the possible direction of causality and the lags we find between timeseries are consistent with carbon dioxide being the response variable.”
“Carbon dioxide is very strongly correlated with sea ice dynamics, with the carbon dioxide rate at Mauna Loa lagging sea ice extent rate by 7 months. Methane is very strongly correlated with sea ice dynamics, with the global (and Mauna Loa) methane rate lagging sea ice extent rate by 5 months. Sea ice melt rate peaks in very tight synchrony with temperature in each Hemisphere.”