Abstract
The atmospheric circulation response to global warming is important for accurate prediction of climate change on regional scales. For the midlatitudes, shifts in the extratropical jet streams have important consequences for precipitation, blocking, and extreme events. It has proven to be a challenge, however, to predict. For example, the North Atlantic jet stream plays a vital role in the climate of eastern North America and Europe; in the last intercomparison of state‐of‐the‐art climate models, the models did not even agree on the sign of its wintertime response to global warming. Perhaps this should not come as a surprise, as we also lack a comprehensive theory for the impact of warming on the midlatitude circulation. In a recent study, Tan et al. (2019, https://doi.org/10.1029/2018MS001492) constructed models of simpler atmospheres to explore the response of the midlatitude jet to global warming. Their idealized atmospheres highlight the difficulty of developing a comprehensive theory for the midlatitude circulation but also provide pathways to improve models of Earth's atmosphere. Models of simpler atmospheres allow one to isolate the impact of specific atmospheric processes and connect theoretical understanding with comprehensive climate prediction systems. Such models can also be used to explore very different atmospheric regimes, from Earth's past to distant planets.
Highlights
Key Points: The atmospheric circulation response to global warming is both a challenge to predict and to understand Models of idealized atmospheres allow a process-oriented investigation of the circulation response A growing number of models of simpler atmospheres are being developed and shared
On Earth, the key players in the infrared, water vapor and carbon dioxide, only interact with certain frequency bands due to their molecular structure, which has a significant impact on how radiative heating and cooling are distributed throughout the atmospheric column
The overall opacity, or thickness of the atmosphere to radiation, is comparable to Earth's atmosphere but exhibits no temporal variation. This is because even though the planet has the equivalent of a hydrological cycle, its condensible “water vapor” is transparent to radiation, and there are no clouds, which would interact with both the outgoing terrestrial and the incoming solar radiation
Summary
Tan et al (2019) were not motivated by recent discoveries of exoplanets: Understanding the response of the storm tracks on these hypothetical worlds has direct relevance to climate change on Earth. We have little confidence in our climate model projections of the atmospheric circulation response to global warming, for the midlatitude jet streams and storm tracks (e.g., Shepherd, 2014; Vallis et al, 2015). This is a big problem for regional climate prediction: We know from observations that shifts in the jet stream impact precipitation and extreme events (e.g., Thompson & Wallace, 2001). The response of the jets in Coupled Model Intercomparison Project 5 models to quadrupled CO2 varies substantially in different seasons and between the North Atlantic and the North Pacific (Grise & Polvani, 2016). Narrowing down the climate sensitivity of our planet may not necessarily improve our ability to project circulation changes
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