Do climate models ever simulate stratospheric water vapour changes comparable to the post-2000 drop?

Observations show a step-wise ~20% decrease in tropical lower stratospheric water vapour (SWV) after 2000. This may have contributed to decadal variability in global surface temperature. It is therefore important that global coupled climate models can capture such extreme anomalies in water vapour entry into the stratosphere. This study examines multi-year to decadal variability in tropical stratospheric water vapour as simulated in CMIP5 models. We examine pre-industrial control and historical scenarios to evaluate both internal and forced variations in tropical lower stratospheric water vapour in the current generation of climate models. The models do not simulate changes in SWV which are comparable in terms of magnitude or persistence to the observed post-2000 decrease. The largest multi-year changes occur in the historical simulations following large tropical volcanic eruptions. The implications for decadal variations in the global energy budget in models will be discussed.