Interests
climate dynamics, internal variability, predictability, sea ice, ocean overturning, ice-ocean-atmosphere interactions, feedbacks
Current Projects
Response of global ocean overturning to orbital forcing
Environmental Science and Engineering, California Institute of Technology
with Andrew Thompson, Emily 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-interglacial 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, general ocean circulation
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, feedbacks
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, general ocean circulation, climate change
Previous Projects
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. Internal variability of the climate system can mask human-induced sea-ice loss on decadal timescales, meaning it must be properly accounted for when interpreting observations and characterizing projections. Using a suite of fully-coupled global climate model ensembles that represent different realizations of internal variability, we studied how internal variability confounds estimates of Arctic sea ice loss in the coming decades.
sea ice, internal variability, climate change, predictability
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, internal variability, 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, feedbacks
Uncertainty in the spatial pattern of warming
Department of Atmospheric Sciences, University of Washington
with Kyle Armour, Gerard 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, feedbacks
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 and the 2020 Graham Cogley Award shortlist).
climate variability, internal 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.
general ocean circulation, ocean overturning, atmospheric circulation