Fig. 2.

Lagged correlations between interannual variations of the atmospheric CO₂ growth rate and tropical (24° S to 24° N) climate variables, including land surface temperature, land precipitation (reversed in sign), and the MEI. Positive time lags indicate that the climate variables lead the CO₂ growth rate. To facilitate comparisons with the findings of previous studies (3, 9), also shown here are the lagged correlations of CO₂ growth rate with land temperatures in northern latitudes (30° N to 70° N), southern latitudes (70° S to 30° S), and over the globe (90° S to 90° N). A time window of 42 y is applied to the time series so they have the same data length and the correlations have the same degrees of freedom. All the land-based climate variables are aggregated only over vegetated areas. The critical values for the correlations at 95% significance levels (i.e., P < 0.05) are estimated through two independent methods including Monte Carlo experiments with 10,000 samples (Data and Methods).