About

Cecilia Bitz is a professor and chair in the Department of Atmospheric Sciences at the University of Washington. Her research focuses on climate and climate change in the high latitudes on Earth, especially involving the cryosphere. She employs a variety of models for her research, ranging from simple reduced models to sophisticated earth-system models. She has worked with several astrobiology students to teach them about climate modeling and conduct simulations relevant for Earth's deep past and exoplanet climates. Her work contributes to understanding the effects of climate dynamics, orbital configurations, and stellar energy distribution on planetary habitability and climate stability, which are relevant for astrobiology and the study of exoplanets.

Research topics

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

Selected publications

• The Strength of Coupling to the Southern Ocean Modulates Tropical Eastern Pacific Variability and Forced Response

  Journal of Climate · 2026-02-04

  article

  Abstract Despite rising global-mean temperatures, large parts of the Southern Ocean and tropical eastern Pacific Ocean have cooled during the satellite era. These regions may be linked by teleconnections, with Southern Ocean cooling contributing to tropical eastern Pacific cooling. We demonstrate that, on average, state-of-the-art Earth system models (ESMs) underestimate the magnitude of interaction between the Southern Ocean and tropical eastern Pacific Ocean. The strength of the teleconnection is shown to be mediated by the magnitude of the positive cloud–sea surface temperature (SST) feedback in the subtropical eastern Pacific Ocean and the strength of the wind–evaporation–SST (WES) feedback. We link excessive precipitation in the tropical Pacific south of the equator to the strength of the Southern Ocean–eastern Pacific teleconnection. This model bias, known as the double intertropical convergence zone (ITCZ), is shown to be related to erroneous convection south of the equator, weakened cross-equatorial trade winds, and unfavorable meteorological conditions for marine boundary layer subtropical clouds. We postulate there is a two-way interaction, in which a double-ITCZ occurs with weaker cloud–SST and WES feedbacks, which in turn impact local SSTs and amplify the double-ITCZ. Models with a stronger Southern Ocean to tropical Pacific teleconnection tend to exhibit more multidecadal variability in the Walker circulation, ITCZ, and west–east equatorial SST gradient, as well as greater delayed warming in the tropical eastern Pacific Ocean resulting from delayed Southern Ocean warming under greenhouse gas forcing. These results provide insight into why ESMs struggle to replicate observed tropical Pacific temperature trend patterns and point to ITCZ location as a key target for improvement in future model development. Significance Statement The key advancement of this study is to demonstrate that, on average, state-of-the-art Earth system models underestimate the magnitude of interaction between the Southern Ocean and tropical east Pacific. As a result, historical cooling in the Southern Ocean may explain a larger fraction of observed east Pacific cooling than previously appreciated. Initial evidence suggests unrealistic precipitation simulated by models in the southeast equatorial Pacific may result in a “blocking” of high latitude influence due to its impact on the magnitude of the cloud–SST feedback and response of easterly trade winds. These results improve our understanding of the processes controlling the Southern Ocean–eastern Pacific teleconnection and provide a guide for future model development and climate trend attribution.

  PublisherDOI

• Regime-dependence when constraining a sea ice model with observations: lessons from a single-column perspective

  2025-06-17

  preprintOpen accessSenior author

  Abstract. A substantial body of work has explored the use of sea ice concentration (SIC) and sea ice thickness (SIT) observations to initialize modeled estimates of the unobserved Arctic sea ice state via data assimilation (DA). While many recent studies have highlighted the particular value of incorporating SIT observations to this end, the influence of local sea ice conditions on the efficacy of assimilating various observation types has not been sufficiently evaluated. This work utilizes a single-column sea ice model to represent three common Arctic sea ice regimes: pack ice, seasonal ice, and first-year ice. An ensemble data assimilation framework is then used to assimilate synthetic observations of SIC, SIT, and two types of sea ice freeboard in each regime. Results demonstrate substantial variation in observation efficacy across observation types and sea ice conditions. In particular, SIT and laser altimeter freeboard observations are found to have a broadly positive impact in thick ice regimes, while SIC effectively constrains thinner, more marginal sea ice regimes. A need for regime-tailored DA strategies and further experimentation with underutilized sea ice observation types is strongly implied.

  PublisherOA PDFDOI

• Sea ice in Earth System Models

  2025-08-06

  other
  PublisherDOI

• Linking the evolution of floe-scale ice characteristics to its deformation history using satellite observations

  2025-03-14

  preprintOpen access

  Arctic sea ice is a mosaic of ice floes whose distribution and thicknesses greatly impact the interaction of sea ice with the atmosphere and the ocean. However, we are still lacking knowledge of the physics to describe the complex interplay of ice floes that are a key characteristic of sea ice. In our contribution, we outline a framework to characterize sea-ice deformation at the floe-scale from observational data by studying the mechanical interaction of multiple identifiable floes. We use Sentinel SAR imagery and ICESat-2 data acquired during the MOSAiC expedition to map ice floes and their thickness in the larger area around Polarstern. This combination of data products allows us to describe the floe-size distribution of floe diameters from tens of kilometers down to tens of meters. With the repeated coverage of SAR imagery, ice motion is tracked and deformation estimates are derived. By combining both floe-size estimates and deformation rates we provide insights into how the floe composition changes in regions that were exposed to deformation and highlight ice fracture as a major source of the power-law distribution of floe sizes. Finally, we present a parameterization of this relationship between floe sizes and ice fracture for large-scale continuum sea-ice models.

  PublisherDOI

• Supplementary material to "Sea Ice Albedo Bounded Data Assimilation and Its Impact on Modeling: A Regional Approach"

  2025-08-08

  articleOpen access

  Adaptive Inflation for Sea Ice DA in QCEFFThe introduction of a bounded DA scheme complicates the use of classical inflation techniques.In traditional ensemble DA, multiplicative inflation is often applied to artificially increase model spread, enhancing the ensemble's ability to capture observed variability (Anderson and Anderson, 1999).However, this approach becomes problematic when applied to bounded variables, which must remain within strict physical limits.For example, during the melt season, SIC within a grid cell can approach zero.When is near zero, inflating the spread by a factor intended for Gaussian distributions can produce ensemble members that fall below zero-an unphysical state-or expand the distribution in a way that still fails to include nearby observed values.If, after inflation, the observation still falls outside the ensemble's acceptable range (here defined as within 2 of the mean), the DA framework may reject it as inconsistent with the model prior.This mismatch highlights the challenge of using symmetric inflation schemes for variables with hard physical bounds and skewed distributions near those bounds.Observation rejections can also occur even when values are not near physical bounds.These rejections stem from insufficient ensemble spread rather than model limitations, especially during rapid changes when diverges from the true model-generated observation.This issue is especially common during the melt season, when fast transitions often associated with albedo feedback and driven by melt-ponding, refreezing, or snowfall introduce variability that bounded ensemble systems struggle to accommodate.To address these challenges, we apply a temporally varying adaptive inflation scheme available in DART, which enforces a minimum model spread (El Gharamti, 2018).This scheme models inflation factors as inverse-gamma distributed random variables.Inflation values evolve over time alongside the ensemble state, with their means and variances updated based on observational input.In our implementation within the QCEFF (Quantile Conserving Ensemble Filter Framework), the adaptive inflation diverges from its original formulation.Rather than enforcing strict bounds through priors or hard constraints-as in traditional bounded inflation schemes-the QCEFF-compatible version emphasizes physical consistency and conservation across the ensemble.This reformulation decouples inflation from rigid statistical boundaries and instead aligns it with the QCEFF's diagnostic balance principles (Anderson, 2022(Anderson, , 2023)).This adaptive inflation framework ensures stability and consistency by preserving the integrity of the initial ensemble spread introduced during the spin-up phase.We fix the minimum inflation factor at 1.0, maintaining the original ensemble spread prior to data assimilation.The upper bound is set at 50.0, although this limit is rarely approached due to the physical constraints imposed by the bounded DA scheme.To regulate how inflation evolves over time, we constrain the standard deviation of the inverse gamma distribution used to sample the inflation factor.Specifically, the distribution's standard deviation must be no smaller than 0.6, ensuring a minimum level of ensemble variability, and the distribution's width is restricted such that the inflation standard deviation cannot grow or shrink by more than a factor of 1.05 per time step.These constraints, informed by

  PublisherDOI

• No longer polar opposites? Similarities in recent Arctic and Antarctic sea ice change

  2025-11-04

  articleOpen access

  Until recently, trends in sea-ice cover in the Arctic and Antarctic seemed to follow opposite pathways. While Arctic sea ice showed a strong and prolonged decrease, Antarctic sea ice displayed a small but significant increase. Yet, in 2015, Antarctic sea ice experienced a sharp decline to an unprecedented summertime low in 2016 and a subsequent year-round minimum in 2023. These series of events have suggested the start of a sustained decline in Antarctic sea ice, similar to that in the Arctic. Meanwhile, the Arctic sea ice is transitioning towards a seasonal regime that resembles that of the Antarctic sea ice. These ongoing changes motivated the workshop on {\it The Role of Sea Ice and its Variability in the Climate System}, which brought together the Arctic and Antarctic research communities in July 2024 at the Abdus Salam International Centre for Theoretical Physics (ICTP) in Trieste, Italy. Here, we synthesize the discussions that took place during the workshop on changes in sea-ice properties as well as on oceanic and atmospheric drivers of these changes. We acknowledged that understanding these drivers requires enhanced observations of sea-ice parameters, such as thickness, improved process representation in models, such as ocean mesoscale eddies, and a more integrated approach to studying both polar regions. Our ability to predict sea ice changes, and hence assess future climate risks, depends on this refined understanding.

  PublisherOA PDFDOI

• Fast, flexible, focused: the case for a single-column sea ice data assimilation framework

  2025-03-15

  preprintOpen accessSenior author

  Assimilating sea ice observations into numerical sea ice and climate models has garnered increasing interest, driven by a demand for more comprehensive sea ice records and forecasts in response to a rapidly changing cryosphere. The development of data assimilation (DA) techniques targeted specifically for sea ice, however, has been comparatively limited.  The computational requirements and structure of many modern sea ice models, the physical characteristics of key sea ice variables, and the uncertainty and relatively limited scope of assimilated sea ice observations all pose significant challenges for the development and tuning of sea ice DA systems. This work presents a new, lightweight framework for sea ice DA development that couples a flexible ensemble DA software to a single-column, multi-category sea ice model, and reviews several recent applications. Key results include the variable impact of common sea ice observation kinds across different sea ice regime types; the benefits of tailoring DA algorithms to the physical and modeled characteristics of sea ice; and the efficacy of assimilating new kinds of observations, including the ice thickness distribution and sea ice albedo. Collectively, these results highlight the ease of experimentation proffered by this new framework, which enables both novel research and more accessible development in sea ice state estimation and forecasting contexts.

  PublisherDOI

• Sea Ice Albedo Bounded Data Assimilation and Its Impact on Modeling: A Regional Approach

  2025-08-08

  preprintOpen accessCorresponding

  Abstract. We conducted a perfect model experiment using Icepack, a one-dimensional single-column sea ice model, to assess the potential of data assimilation (DA) to improve predictions of the mean sea ice state through the incorporation of sea ice albedo (SIAL) observations. One ensemble member is designated as the TRUTH, and synthetic observations drawn from it are assimilated into the remaining ensemble members. DA is carried out using the Data Assimilation Research Testbed (DART) with a bounded Quantile Conserving Ensemble Filtering Framework (QCEFF), which accounts for the bounded nature of sea ice variables. Icepack ensembles were spun-up for four Arctic locations based on small perturbations to atmospheric forcing. Results show that assimilating SIAL yields comparable or superior performance to more commonly assimilated observables such as sea ice concentration (SIC) and thickness (SIT) in three-quarters of the Arctic regions studied, and across all regions when observational uncertainty in SIAL is reduced below estimates from the current literature. These findings underscore the value of leveraging existing SIAL observations and expanding their temporal and spatial coverage in the Arctic. Furthermore, the study highlights the critical need to better constrain the observational uncertainty of SIAL. Enhanced observational networks would provide the necessary validation data, enabling more accurate uncertainty characterization and improved sea ice forecasts in a rapidly evolving polar climate.

  PublisherOA PDFDOI

• Artificial Flooding Leads to Thicker and Brighter Arctic Sea Ice

  Earth s Future · 2025-12-12

  articleOpen access

  Abstract We describe and present results from a 2024/2025 field campaign that is the first to test and observe the impact of flooding and meltwater draining on Arctic sea ice over the winter growth and spring melt seasons. The campaign was conducted in Cambridge Bay, Nunavut, Canada. A 1 by 1 km fieldwork site was used, comprising three control areas, which were never flooded, and eight test areas. In these, flooding treatments were carried out by pumping seawater onto the sea ice. Some test areas were flooded once (in December or January), while others were flooded twice (in December and February, or January and February). The total area flooded was 0.25 . Additionally, one control area was used for a melt pond drainage experiment during spring. By mid May, prior to melt, flooded test areas were up to 32 cm thicker than control areas, with snow cover that was 1–13 cm thinner. Areas flooded twice exhibited greater thickening than those flooded once. During the melt period, sea ice in the flooded areas appeared brighter and showed slower melt rates, remaining thicker than that in the control areas. The drained melt pond site also brightened markedly within 1 week of borehole drilling. Comparison with a historical sea ice thickness record from Cambridge Bay indicates that a 30 cm increase corresponds to roughly the magnitude of long‐term thinning observed over the past 50 years.

  PublisherDOI

• Dark land surfaces allow for habitable land that could support  photosynthetic life on the surface of Snowball Earth

  2025-02-21

  preprintOpen access

  Photosynthetic eukaryotic algae survived the Neoproterozoic Snowball Earth events, indicating that liquid-water refugia existed somewhere on the surface. We examine the potential for refugia at the coldest time of a snowball event, before CO 2 had risen and with high-albedo ice on the frozen ocean, before it became darkened by dust deposition. We use the Community Earth System Model to simulate a “modern” Snowball Earth (i.e., with continents in their current configuration), in which the ocean surface has frozen to the equator as “sea glaciers”, hundreds of meters thick, flowing like ice shelves. Despite global mean surface temperatures below -60°C, some areas of the land surface reach above-freezing temperatures because they are darker than the ice-covered ocean. With low CO 2 (10 ppm) and land-surface albedo characteristic of bright sand-deserts (0.4), 0.1 percent of the land surface could host liquid water seasonally; this increases to 12 percent for darker land of albedo characteristic of polar deserts (0.2). Given a water source to these locations, such as a narrow bay intruding from the ocean like the modern Red Sea, photosynthetic life could survive on warm, bare land. The abundance of habitable land and consequently potential refugia increases more strongly in response to reducing the land albedo than to higher CO 2, for the same global radiative forcing.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Polar Amplification and High-Latitude Climate Sensitivity in Global Climate Models

  NSF · $293k · 2003–2007

• Deciphering the Antarctic MSA-sea Ice Link with a Combined Regional Forecast and Atmospheric Chemistry Model

  NSF · $375k · 2008–2012

• Short-term predictability of Arctic climate

  NSF · $308k · 2009–2013

• The Mutual Interaction Between Ice Production and Ocean Heat Transport in a Greenhouse Warming Scenario

  NSF · $324k · 2005–2009

• Collaborative Research: Rapic Climate Change due to Sea Ice Dynamics in the North Atlantic and Arctic Oceans

  NSF · $352k · 2005–2009

Frequent coauthors

• Edward Blanchard‐Wrigglesworth

  University of Washington

  61 shared

• Kyle C. Armour

  43 shared

• Marika M. Holland

  40 shared

• David S. Battisti

  University of Washington

  39 shared

• Lettie A. Roach

  Columbia University

  36 shared

• Martin Vancoppenolle

  Sorbonne University Abu Dhabi

  32 shared

• François Massonnet

  UCLouvain

  30 shared

• Eric J. Steig

  University of Washington

  24 shared

Education

• Ph.D., Atmospheric Sciences

  University of Washington

  1994

• M.S., Atmospheric Sciences

  University of Washington

  1991

• B.S., Atmospheric Sciences

  University of California, Berkeley

  1988