In response to global warming, climate models predict a weakening of the Walker Circulation (WC). This is supported by long-term sea level pressure observations over the 20th century. However, my work shows that the observations and multiple reanalyses yield a WC intensification from 1979 to the present,  opposite to what model predicts. Atmosphere-only simulations (AMIP) simulate this observed intensification, whereas coupled model simulations (CMIP) do not. Thus, the recent WC intensification is related to real-world SST evolution. Assume that the observed SSTs can be decomposed into a forced and an unforced component. Idealized CAM5 simulations driven by the unforced component of SSTs (CAM5 UFSST) yield significant WC strengthening, whereas negligible WC changes occur when driven by the forced component of SSTs (CAM5 FSST). Although coupled climate models may be deficient in their tropical response to anthropogenic warming, our results suggest natural SST variability, and in particular, a La Niña-like SST pattern is primarily responsible for the strengthening of the WC since 1979. (Zhao, X. and Allen, R.J. 2019. Environmental Research Communications,)