Background: The seasonal cycle of atmospheric carbon dioxide is usually ascribed to the seasonality of Northern Hemisphere vegetation, and the seasonal cycle of methane is usually ascribed to seasonal removal by the hydroxyl radical.
Objective: We test an alternative, that the cycles of these greenhouse gases might be linked to sea ice dynamics.
Method: Time-series analysis of carbon dioxide, methane, sea ice parameters, vegetation greenness (NDVI), and temperature. We consider a variable that lags another can not be causal of the leading variable.
Results: 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. The very high synchrony of the two gases is most parsimoniously explained by a common causality acting in both Hemispheres.
Conclusion: Time lags between variables indicate primary drivers of the gas dynamics are due to solar action on the polar regions, not mid-latitudes as is conventionally believed. Our results are consistent with a proposed role of a high-latitude temperature-dependent abiotic variable such as sea ice in the annual cycles of carbon dioxide and methane. If sea ice does not drive the net flux of these gases, it is a highly precise proxy for whatever does. Potential mechanisms should be investigated urgently.
