Interests

climate change, climate variability, predictability, sea ice, ocean overturning, and ice-ocean-atmosphere interactions

Current Projects

Response of global ocean overturning to orbital forcing

Environmental Science and Engineering, California Institute of Technology

with Andrew ThompsonEmily Newsom, and Jess Adkins

Understanding how the general ocean circulation reconfigures itself due to orbital forcing is important for interpreting past behavior, especially during glacial cycles. Here, we are using a fully-coupled climate model that was forced with a range of greenhouse-gas concentrations and different combinations of obliquity and precession to study the equilibrium structure of ocean circulation after experiencing large changes in external forcing.

ocean overturning

Constraints on the loss of Arctic sea ice

Environmental Science and Engineering, California Institute of Technology

with Tapio Schneider, Ian Eisenman, and Robert Wills

Projections of Arctic sea ice remain uncertain. In order to reduce this uncertainty, the processes that constrain the long-term evolution of sea ice need to be better understood. Using an ensemble of fully-coupled global climate models we are studying the physical processes that govern the evolution of Arctic sea ice, with a particular focus on processes that cause the spread in climate model projections.

sea ice, climate change

Transient and equilibrium responses of ocean heat transport and overturning to warming

Environmental Science and Engineering, California Institute of Technology

with Andrew Thompson, Emily Newsom, Shantong Sun, and Maria Rugenstein

Understanding how ocean overturning responds to increasing greenhouse gas concentrations is important for predicting future changes. Recent work has  renewed interest in the role of inter-basin heat exchange in controlling global ocean overturning. Here, we are using a suite of fully-coupled climate models that were forced with a range of greenhouse-gas concentrations to study the transient and equilibrium responses of ocean heat transport and circulation to warming.

ocean overturning, climate change

Uncertainty in projections of Arctic sea ice

Environmental Science and Engineering, California Institute of Technology

with Flavio Lehner and Marika Holland

Arctic sea ice has declined rapidly over the past few decades and is projected to continue declining in the coming decades. However, internal climate variability can mask human-induced sea-ice loss on decadal timescales, meaning it must be properly accounted for when considering observations and understanding projections. Using a suite fully-coupled global climate model ensembles that represent different realizations of internal climate variability, we are studying how internal variability confounds estimates of Arctic sea ice loss in the coming decades.

sea ice, climate change, predictability

Previous Projects

Influence of the Pacific Ocean on Arctic sea ice 

Department of Atmospheric Sciences, University of Washington 

with Ed Blanchard-Wrigglesworth

Our understanding of atmospheric teleconnections is derived from the temporally-limited observational record, which means we are only seeing a glimpse of these patterns. Using an ensemble of fully-coupled global climate models, we studied how a relationship between the Pacific Ocean and Arctic sea ice evolves in time and showed that this relationship is non-stationary in time. In the context of observed Arctic sea ice, when this mode shifts in the future, we can expect significant changes to the magnitude of sea ice loss (see Bonan and Blanchard-Wrigglesworth, 2020).

sea ice, ice-ocean-atmosphere interactions, predictability

Regional predictions of Arctic sea ice

Geophysical Fluid Dynamics Laboratory (GFDL), National Oceanic and Atmospheric Administration (NOAA)

with Mitch Bushuk and Mike Winton

Accurately predicting Arctic sea ice is of interest to many stakeholders, including indigenous communities, fisheries, and the shipping industry. Using an ensemble of fully-coupled global climate models and a simple linear regression model, we demonstrated that there is a robust springtime predictability barrier across dynamical models, which suggests there is a fundamental limit on accurate forecasts of regional Arctic sea ice and a physical mechanism universal to all global climate models (see Bonan et al., 2019 and Bushuk et al., 2020).

predictability, sea ice 

Response of the hydrologic cycle to global warming

Department of Atmospheric Sciences, University of Washington 

with Kyle Armour, Gerard Roe, and Nick Siler

Idealized models allow us to better understand the behavior of comprehensive global climate models. Recent studies have shown that a simple model that makes an assumption about how atmospheric heat transport behaves is remarkably successful at emulating the response of climate models to an increase of CO2. Through the lens of this simple model, we characterized the spread in the predicted patterns of evaporation and precipitation made by climate models under global warming.

climate change

Uncertainty in the spatial pattern of warming

Department of Atmospheric Sciences, University of Washington

with Kyle ArmourGerard Roe, Nick Siler, and Nicole Feldl

As global climate models have increased in complexity, the number of physical processes representing the climate system has also increased. A central goal of climate science is to understand how uncertainty in these physical processes translates into uncertainty in the forced response. Within climate models, though, it is a challenge to disaggregate the individual factors contributing to uncertainty and explore each in a systematic way. To circumvent this problem, we used a simple model —  which describes how energy is transported from the tropics to the poles — to study uncertainty in the spatial pattern of warming (see Bonan et al., 2018 and this EOS spotlight).

climate change 

Glacier trends and natural variability in the climate system

Department of Earth and Space Sciences, University of Washington

with Knut Christianson and John Christian

Glacier retreat is an iconic symbol of climate change. Mass loss from any particular glacier, however, is the result of both anthropogenic and natural changes. Using a statistical method known as dynamical adjustment, we studied how circulation anomalies affect seasonal glacier mass-balance trends to quantify the influence of natural variability on glacier mass loss in the North Atlantic (see Bonan et al., 2019).

climate variability, ice-ocean-atmosphere interactions

Effects of orography on large-scale atmospheric and oceanic circulation 

Department of Atmospheric Sciences, University of Washington

with Dargan Frierson and Rachel White 

Mountains play an important role in shaping the Earth's climate. Not only do these features modulate the circulation of the atmosphere, but they also control the strength of circulation in the ocean through changes in precipitation and wind patterns. By running idealized experiments in which mountains were removed from specific geographic regions in global climate models, we studied the influence of orography on large-scale oceanic and the atmospheric circulation.

ocean circulation, ocean overturning, atmospheric circulation