Research Highlights

Recent and ongoing research shows that atmospheric radiative feedbacks depend on changes in sea-surface temperature patterns (“pattern effect”) and global mean temperature (“feedback temperature dependence”). This implies that feedbacks can change as warming patterns and global temperature evolve over time, counter to what has been assumed for decades. This realization has led to a proliferation of feedback definitions and methods to estimate equilibrium climate sensitivity (ECS). In a recent Geophysics Research Letters paper, Rugenstein and Armour contrast the equilibrium, effective, and differential feedback parameter definitions and discuss their physical interpretations and applications. Importantly, these feedback definitions imply different values of effective or equilibrium climate sensitivity.

Densely populated regions located at the mid-latitude Northern Hemisphere have been hit by extreme winter weather in recent years. In a recent paper by Yin and Zhao, the authors use a state-of-the-art global weather/climate modeling system with high resolution to better understand the role of the AMOC in the US extreme cold weather.

From 2013-2016, northeast Pacific Ocean experienced an extreme marine heatwave extending from Gulf of Alaska to Baja California. During this time, California suffered from a multi-year drought. Will these compound extremes occur more frequently in the future under global warming? A new study by Shi et al. shows that such events along the West Coast were unusual in the past and in the future, similar conditions will increase.

Continued increases in concentrations of well-mixed greenhouse gases in the atmosphere has led to a net gain of energy by Earth. Most of this excess energy warms the ocean, with the remainder heating the land, melting snow and ice, and warming the atmosphere. This Earth energy imbalance (EEI) is responsible for the unprecedented changes in surface temperature, sea level, precipitation patterns, and extreme weather that have been observed in recent decades. A new study by Loeb and co-authors reveals that both satellite observations and in situ planetary heat uptake measurements independently show an approximate doubling of EEI from mid-2005 to mid-2019.

How does a rapidly warming Arctic affect mid-latitude climate now and future years? Literature on this subject shows contrasting results, in part due to differences in protocols when modeling the climate response to Arctic sea-ice loss. Recommended by PAMIP, a common practice to smooth out noise of atmospheric variability (a major source of uncertainty in response to sea-ice loss) is to run ensembles (>100 ensemble members) of simulations. However, a recent study by Peings et al. shows that having 100 ensemble members in fact does not guarantee a robust assessment of the response.