The covariation of Northern Hemisphere summertime CO2 with surface temperature in boreal regions

We analyze interannual variability in the strength of the seasonal cycle drawdown in northern midlatitudes from measurements of CO₂ made by the Total Carbon Column Observing Network (TCCON) and from the Greenhouse Gases Observing Satellite (GOSAT). We find that the variability correlates with surface temperature in the boreal regions. The XCO₂ seasonal cycle minima in TCCON data increases by 1.2 × 0.7 ppm/K. Assimilations from CarbonTracker 2011 and CO₂ simulations using the Simple Biosphere exchange Model (SiB3) transported by GEOSChem underestimate this covariation, but suggest that both atmospheric transport and biospheric activity contribute to the observed covariation. The slope of the correlation in both the data and in the models near western Europe is systematically smaller than those at other locations in the northern mid-latitudes. This may reflect, in part, the role of local fossil fuel fluxes.