About

The faculty, staff and students in the Department of Atmospheric and Climate Science at the University of Washington are engaged in the study of a broad range of atmospheric phenomena and processes, using methods ranging from mathematical analysis to field experimentation. Research projects range in size from small studies involving individual scientists to large national and international programs involving teams of scientists. Research groups in the department are concerned with Atmospheric Chemistry, Atmospheric Dynamics, Boundary Layer Processes, Cloud and Aerosol Research, Glaciology and Planetary Atmospheres, Cloud Dynamics, Precipitation Processes, Storms, Weather Analysis and Forecasting, Climate, Global change, Airflow over mountains, and other topics. Some groups maintain special research facilities for the use of their students. In some of these activities, there is close cooperation with the University of Alaska Fairbanks, Oregon State University and the National Oceanic and Atmospheric Administration (NOAA) Regional Center through the Cooperative Institute for Climate, Ocean and Ecosystem Studies. Faculty members often have interests in more than one area, and research projects frequently involve questions of broad scope which do not fall neatly into a single category. This is particularly true of research projects directed toward understanding the chemical and physical modification of the environment by human activities.

Research topics

• Climatology
• Geology
• Oceanography
• Atmospheric sciences
• Geography
• Environmental science
• Meteorology

Selected publications

• Understanding AMOC changes resulting from varying historical radiative forcings

  2026-03-14

  articleOpen access

  A potential Atlantic Meridional Overturning Circulation (AMOC) slowdown, possibly caused by external forcings, is widely debated, and its historical drivers and future evolution remain uncertain. Here we disentangle the effects of greenhouse gases and anthropogenic aerosols on the AMOC and on other relevant processes in the high-latitude North Atlantic (NA) over 1850–2014. We analyze a multi-model ensemble of experiments from the Large Ensemble Single Forcing Model Intercomparison Project, specifically: hist-GHG (varying concentrations of greenhouse gases, other forcings constant) and hist-aer (same as hist-GHG, but for anthropogenic aerosols), and we compare these to the respective CMIP6 historical simulations (all forcings varying) and observational datasets.Robust AMOC weakening under hist-GHG and strengthening under hist-aer is found across the respective multi-model ensembles with various accompanying changes, exhibiting a high degree of spatial antisymmetry. In both sets of experiments, the same causal pathway (yet with opposite sign) occurs. We describe the key role of subpolar upper-ocean salinity and connect its variations to changes in sea ice and air–sea heat fluxes. Our results indicate that the primitive radiative forcing directly impacts sea-ice mass, and thereby drives upper-ocean salinity variations, while accompanying changes in surface freshwater fluxes further modulate salinity. The resulting variations in salinity induce changes in upper-ocean density and stratification in the subpolar NA that, in turn, determine the simulated AMOC trends. We further discuss key mechanisms in play, including the positive AMOC–salinity and AMOC–evaporation feedbacks, describing the dominant processes of the causal pathway.By offering insights onto the respective roles of external forcings in the context of climate change and by advancing our understanding of key NA ocean–atmosphere interactions, our results also highlight models limitations in the representation of coupled processes that are critical for reliable projections.

  PublisherDOI

• Global hotspots of large precipitation extremes

  Research Square · 2025-09-16

  preprintOpen access
  PublisherOA PDFDOI

• Linking carbon cycling to climate feedbacks in a simple climate model for decarbonization

  2025-03-14

  preprintOpen access

  Complex models of the Earth system are increasingly able to represent processes that make up the carbon-climate system, but a variety of simple climate models (SCMs) use parameterized representations of the Earth system, which make them easily deployed tools for climate mitigation assessment and accessible tools for conceptual understanding. However, SCMs vary in their approach to simplifying the Earth system, especially in their representation of the carbon cycle. We examine how two distinct carbon cycle structures within one SCM, FaIR, produce differing constrained projections of future climate under idealized decarbonization. We find that differences in carbon cycle structure lead to differences in the timescales of carbon uptake, which do not directly lead to or explain differences in warming under the same decarbonization emissions scenario. Differences in the metrics of warming are instead primarily explained by assumptions about climate feedbacks and non-carbon cycle forcing, which are parameterized separately from carbon cycling. When we introduce a physically-motivated link reflecting the connection between ocean circulation and energy balance, we see a change in the set of climate feedbacks necessary to explain our observed carbon-climate system. The result is a shift in TCRE, ZEC, and consequent necessary mitigation.

  PublisherDOI

• Increasing boreal fires reduce future global warming and sea ice loss

  Proceedings of the National Academy of Sciences · 2025-06-03 · 10 citations

  articleOpen accessSenior author

  Biomass burning can affect climate via the emission of aerosols and their subsequent impact on radiation, cloud microphysics, and surface and atmospheric albedo. Biomass burning emissions (BBEs) over the boreal region have strongly increased during the last decade and are expected to continue increasing as the climate warms. Climate models simulate aerosol processes, yet historical and future Coupled Model Intercomparison Project (CMIP) simulations have no active fire component, and BBEs are prescribed as external forcings. Here, we show that CMIP6 used future boreal BBEs scenarios with unrealistic near-zero trends that have a large impact on climate trends. By running sensitivity experiments with ramped up boreal emissions based on observed trends, we find that increasing boreal BBEs reduces global warming by 12% and Arctic warming by 38%, reducing the loss of sea ice. Tropical precipitation shifts southward as a result of the hemispheric difference in boreal aerosol forcing and subsequent temperature response. These changes stem from the impact of aerosols on clouds, increasing cloud droplet number concentration, cloud optical depth, and low cloud cover, ultimately reducing surface shortwave flux over northern latitudes. Our results highlight the importance of realistic boreal BBEs in climate model simulations and the need for improved understanding of boreal emission trends and aerosol-climate interactions.

  PublisherOA PDFDOI

• Why Do CO₂ Quadrupling Simulations Warm More Than Twice as Much as CO₂ Doubling Simulations in CMIP6?

  Geophysical Research Letters · 2024-05-17 · 3 citations

  articleOpen access

  Abstract We compare abrupt CO 2 ‐quadrupling (abrupt‐4xCO2) and ‐doubling (abrupt‐2xCO2) simulations across 10 CMIP6 models. Two models (CESM2 and MRI‐ESM2‐0) warm substantially more than twice as much under abrupt‐4xCO2 than abrupt‐2xCO2, which cannot be explained by the non‐logarithmic scaling of CO 2 forcing. Using an energy balance model, we show that increased warming rates within these two models are driven by both less‐negative radiative feedbacks and smaller global effective heat capacity under abrupt‐4xCO2. These differences are caused by a decrease in low cloud cover and shallower ocean heat storage, respectively; both are linked to smaller fractional declines in the Atlantic Meridional Overturning Circulation (AMOC) under abrupt‐4xCO2 (relative to abrupt‐2xCO2). On a global scale, higher climate sensitivity under larger forcing can be explained by a feedback‐temperature dependence; however, we find that forcing‐dependent spatial warming patterns due to AMOC decline are an important physical mechanism which reduces warming in a way that is not captured by a global‐mean framework.

  PublisherOA PDFDOI

• Increasing boreal fires reduce future global warming and sea ice loss

  Research Square · 2024-12-04

  preprintOpen accessSenior author
  PublisherDOI

• Atmosphere and ocean energy transport in extreme warming scenarios

  PLOS Climate · 2024-02-01 · 3 citations

  articleOpen accessCorresponding

  Extreme scenarios of global warming out to 2300 from the SSP5-8.5 extension scenario are analyzed in three state-of-the-art climate models, including two models with climate sensitivity greater than 4.5°C. The result is some of the largest warming amounts ever seen in simulations run over the historical record and into the future. The simulations exhibit between 9.3 and 17.5°C global mean temperature change between pre-Industrial and the end of the 23rd century. The extremely large changes in global temperature allow exploration of fundamental questions in climate dynamics, such as the determination of moisture and energy transports, and their relation to global atmosphere-ocean circulation. Three models performed simulations of SSP5-8.5 to 2300: MRI-ESM2-0, IPSL-CM6A-LR, and CanESM5. We analyze these simulations to improve understanding of climate dynamics, rather than as plausible futures. In the model with the most warming, CanESM5, the moisture content of the planet more than doubles, and the hydrologic cycle increases in intensity. In CanESM5 and IPSL-CM6A-LR nearly all sea ice is eliminated in both summer and winter in both hemispheres. In all three models, the Hadley circulation weakens, the tropopause height rises, and storm tracks shift poleward, to varying degrees. We analyze the moist static energy transports in the simulations using a diffusive framework. The dry static energy flux decreases to compensate for the increased moisture transport; however the compensation is imperfect. The total atmospheric transport increases but not as quickly as expected with a constant diffusivity. The decrease in eddy intensity plays an important role in determining the energy transports, as do the pattern of cloud feedbacks and the strength of ocean circulations.

  PublisherOA PDFDOI

• A New Method for Calculating Instantaneous Atmospheric Heat Transport

  Journal of Climate · 2024-05-20

  articleSenior author

  Abstract Atmospheric heat transport (AHT) is an important piece of our climate system but has primarily been studied at monthly or longer time scales. We introduce a new method for calculating zonal-mean meridional AHT using instantaneous atmospheric fields. When time averaged, our calculations closely reproduce the climatological AHT used elsewhere in the literature to understand AHT and its trends on long time scales. In the extratropics, AHT convergence and atmospheric heating are strongly temporally correlated suggesting that AHT drives the vast majority of zonal-mean atmospheric temperature variability. Our AHT methodology separates AHT into two components (eddies and the mean meridional circulation) which we find are negatively correlated throughout most of the mid- to high latitudes. This negative correlation reduces the variance in the total AHT compared to eddy AHT. Last, we find that the temporal distribution of the total AHT at any given latitude is approximately symmetric.

  PublisherDOI

• Increasing boreal fires reduce future global warming and sea ice loss

  Research Square · 2024-11-22

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Trends in Atmospheric Heat Transport Since 1980

  Journal of Climate · 2023-12-22 · 8 citations

  article

  Abstract We investigate the linear trends in meridional atmospheric heat transport (AHT) since 1980 in atmospheric reanalysis datasets, coupled climate models, and atmosphere-only climate models forced with historical sea surface temperatures. Trends in AHT are decomposed into contributions from three components of circulation: (i) transient eddies, (ii) stationary eddies, and (iii) the mean meridional circulation. All reanalyses and models agree on the pattern of AHT trends in the Southern Ocean, providing confidence in the trends in this region. There are robust increases in transient-eddy AHT magnitude in the Southern Ocean in the reanalyses, which are well replicated by the atmosphere-only models, while coupled models show smaller magnitude trends. This suggests that the pattern of sea surface temperature trends contributes to the transient-eddy AHT trends in this region. In the tropics, we find large differences between mean-meridional circulation AHT trends in models and the reanalyses, which we connect to discrepancies in tropical precipitation trends. In the Northern Hemisphere, we find less evidence of large-scale trends and more uncertainty, but note several regions with mismatches between models and the reanalyses that have dynamical explanations. Throughout this work we find strong compensation between the different components of AHT, most notably in the Southern Ocean where transient-eddy AHT trends are well compensated by trends in the mean-meridional circulation AHT, resulting in relatively small total AHT trends. This highlights the importance of considering AHT changes holistically, rather than each AHT component individually.

  PublisherDOI

Recent grants

• Local and Remote Influences on the Intertropical Convergence Zone in a Hierarchy of Models

  NSF · $369k · 2014–2018

• Hemispheric Energy Balance and Tropical Precipitation Shifts: The Impacts of Forcing Location

  NSF · $594k · 2017–2022

• The Effect of Moist Processes on Midlatitude Static Stability

  NSF · $329k · 2010–2014

• CAREER: The Effect of Latent Heating on the Hadley Circulation

  NSF · $576k · 2009–2015

Frequent coauthors

• Yen‐Ting Hwang

  National Taiwan University

  17 shared

• Jacob Scheff

  University of North Carolina at Charlotte

  17 shared

• Gerard H. Roe

  University of Washington

  16 shared

• Sarah M. Kang

  Ulsan National Institute of Science and Technology

  15 shared

• Aaron Donohoe

  University of Washington

  14 shared

• Adam H. Sobel

  13 shared

• David S. Battisti

  University of Washington

  13 shared

• Kyle C. Armour

  12 shared

Awards & honors

• Department of Atmospheric Sciences Annual Teaching Award, 20…
• NSF CAREER Faculty Early Career Development Award, 2009-2014
• University of Washington Royalty Research Fund Award, 2009-2…
• NOAA Climate and Global Change Postdoctoral Fellowship, 2005…
• National Science Foundation Graduate Research Fellowship, 20…