<p>El Niño–Southern Oscillation (ENSO) has major impacts on the weather and climate across many regions of the world. Understanding how these teleconnections may change in the future is therefore an important area of research. Here, we use simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate future changes in ENSO teleconnections in the North Pacific/North America sector.</p><p>Precipitation over the equatorial Pacific associated with ENSO is projected to shift eastwards under global warming as a result of greater warming in the east Pacific, which reduces the barrier to convection as the warm pool expands eastwards. As a result, there is medium confidence (IPCC AR5 report) that ENSO teleconnections will shift eastwards in the North Pacific/North America sector. In the CMIP6 models, the present day teleconnection is relatively well simulated, with most models showing an anomalously deep Aleutian low and associated positive temperature anomalies over Alaska and northern North America in El Niño years. In the future warming simulations (we use abrupt-4xCO2, in which CO2 concentrations are immediately quadrupled from the global annual mean 1850 value), in agreement with the IPCC AR5 report, the North America teleconnection and associated circulation change is shifted eastwards in most models. However, it is also significantly weaker, with the result that the positive temperature anomalies in El Niño years over North America are much reduced. This weakening is seen both in models with a projected increase and projected decrease in the amplitude of future El Niño events. The mechanisms related to these projected changes, along with potential implications for future long range predictability over North America, will be discussed.</p>

<p>Projections of future West African monsoon (WAM) precipitation change in response to increased greenhouse gases are uncertain, and an improved understanding of the drivers of WAM precipitation change is needed to help aid model development and better inform adaptation policies in the region. Here, we address two of these drivers: the direct radiative effect of increased CO<sub>2</sub> (referring to the impact of increased CO<sub>2</sub> in the absence of SST changes), and the impact of a uniform SST warming. Atmosphere only models are used to investigate the response, finding that these two drivers have opposing impacts on WAM precipitation. In response to the direct radiative effect, an increase in precipitation is caused by a northward shift and a weakening of the shallow meridional circulation over West Africa, advecting less dry air into the monsoon rainband. In contrast, the uniform SST warming causes a decrease in precipitation due to a strengthening of the shallow meridional circulation and enhanced moisture gradients between the moist monsoon airmass and the dry desert airmass. These changes in the shallow meridional circulation are shown to be caused by large scale temperature changes as well as the more localised impact of a soil moisture feedback mechanism over the Sahel. It is then shown that the processes discussed are relevant to the intermodel uncertainty in WAM projections across a range of CMIP6 models.</p>

No abstract

No abstract

No abstract