Lettie Roach, PhD

Polar climate scientist


About Me

I am an Associate Research Scientist at the Center for Climate Systems Research, Columbia University based at NASA Goddard Institute for Space Studies (GISS) in New York City.

I am broadly interested in Earth's climate system, with a focus on the polar regions. My research aims to better understand the physics of coupled interactions between ice and climate. I typically work with climate models of varying levels of complexity, in combination with observations, aiming to improve climate projections.


Pancake sea ice floes in the marginal ice zone

Marginal ice zone physics

The marginal ice zone is a dynamic region between dense interior sea ice and the open ocean. I previously developed a model for the sea ice floe size distribution that allowed interactions between sea ice and ocean surface waves to be represented in climate models for the first time. I am interested in further investigating the complex interactions between ocean surface waves and sea ice in this region, which may lead to enhanced melting and retreat of sea ice in a warming climate.

Related publications: Roach, Horvat et al. (2018), Roach, Bitz et al. (2019)

Historical and future sea ice change

The latest climate models suggest that the Arctic will become practically sea-ice-free before 2050. Future changes in Antarctic sea ice are much more uncertain, as models differ from satellite observations over the recent historical period where observations are available. I have led efforts evaluating Antarctic sea ice in climate models compared to observations. Recent work nudging winds towards values from reanalysis reveals successes and biases in the simulation of historical Arctic and Antarctic sea ice.

Related publications: Roach, Dean et al. (2018), Roach, Doerr et al. (2020), Blanchard-Wrigglesworth, Roach et al. (2021), Roach and Blanchard-Wrigglesworth (2022)

September Arctic sea ice in CMIP6 climate models

The Ross Ice Shelf, Antarctica, 2017

Ice sheet-climate coupling

Freshwater from the melt of ice sheets on Greenland and Antarctica is a key contributor to sea level rise and impacts global ocean circulation. I am working on validating and testing a coupled ice sheet configuration for the NASA GISS climate model.

Fundamental drivers of sea ice seasonality

The time taken for sea ice to retreat from its maximum area to its minimum area each year is significantly longer in the Arctic than the Antarctic. Our recent work using an idealized climate model shows that the explanation for the fast seasonal retreat of Antarctic sea may be simpler than previously thought.

Related publications: Roach et al. (2022)

Drone operations on the PIPERS cruise

Integrating observations and models

I am interested in integrating observations with models to better understand and predict polar change. I have been fortunate to participate in fieldwork in the Arctic and Antarctic, both great learning experiences that led to new collaborations.

Related publications: Roach, Smith et al. (2018), Ackley et al. (2020)


Also see Google Scholar

[26] Roach, L. A. and Meier, W.N. (2024). Sea ice in 2023. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-024-00542-0. [Download paper]

[25] Roach, L. A., Mankoff, K., Romanou, A., Blanchard-Wrigglesworth, E., Haine, T., and Schmidt, G. A. (2023). Winds and meltwater together lead to Southern Ocean Surface cooling and sea ice expansion. Geophysical Research Letters, 50, e2023GL105948. https://doi.org/10.1029/2023GL105948

[24] Schmidt, G. A., Romanou, A., Roach, L. A., Mankoff, K., Li, Q., Rye, C. D., Kelley, M., Marshall, J. C. and Busecke, J. J. M. (2023). Anomalous meltwater from ice sheets and ice shelves is a historical forcing. Geophysical Research Letters, 50, e2023GL106530. https://doi.org/10.1029/2023GL106530

[23] Roach, L. A., Eisenman, I., Wagner, T. J. and Donohoe, A. (2023). Asymmetry in the seasonal cycle of zonal-mean surface air temperature. Geophysical Research Letters 50, e2023GL103403. https://doi.org/10.1029/2023GL103403

[22] Goosse, H., Allende Contador, S., Bitz, C. M., Blanchard-Wrigglesworth, E., Eayrs, C., Fichefet, T., Himmich, K., Huot, P.-V., Klein, F., Marchi, S., Massonnet, F., Mezzina, B., Pelletier, C., Roach, L. A., Vancoppenolle, M., and van Lipzig, N. P. M. (2023). Modulation of the seasonal cycle of the Antarctic sea ice extent by sea ice processes and feedbacks with the ocean and the atmosphere. The Cryosphere, 17, 407–425. https://doi.org/10.5194/tc-17-407-2023

[21] Roach L. A., Blanchard-Wrigglesworth, E., Ragen, S., Cheng, W., Armour, K. C., and Bitz, C.M. (2022). The impact of winds on AMOC in a fully-coupled climate model. Geophysical Research Letters 49, e2022GL101203. https://doi.org/10.1029/2022GL101203

[20] Cooper V. T., Roach L. A., Thomson J., Brenner S. D., Smith M. M., Meylan M. H., and Bitz C. M. (2022). Wind waves in sea ice of the western Arctic and a global coupled wave-ice model. Phil. Trans. R. Soc. A. 380:20210258. http://doi.org/10.1098/rsta.2021.0258. [Download paper]

[19] Roach, L. A., Eisenman, I., Wagner, T. J., Blanchard-Wrigglesworth, E., and Bitz, C. M. (2022). Asymmetry in the seasonal cycle of Antarctic sea ice due to insolation. Nature Geoscience. https://doi.org/10.1038/s41561-022-00913-6. [Download paper]. [Download Supplementary]

[18] Roach, L. A. and Blanchard-Wrigglesworth, E. (2022). Observed winds crucial for September Arctic sea ice loss. Geophysical Research Letters, 49, e2022GL097884. https://doi.org/10.1029/2022GL097884. [Download paper]

[17] Montiel, F., Kohout, A., and Roach, L. A. (2022). Physical drivers of wave attenuation in the marginal ice zone. Journal of Physical Oceanography, 52(5), 889-906. https://doi.org/10.1175/JPO-D-21-0240.1. [Download paper]

[16] Horvat, C. and Roach, L. A. (2022). WIFF1. 0: A hybrid machine-learning-based parameterization of Wave-Induced sea-ice Floe Fracture. Geoscientific Model Development 15(2), 803-814 https://doi.org/10.5194/gmd-15-803-2022

[15] Blanchard-Wrigglesworth, E., Donohoe, A., Roach, L. A., DuVivier, A., and Bitz, C. M. (2021). High-frequency sea ice variability in observations and models. Geophysical Research Letters, 48, e2020GL092356. https://doi.org/10.1029/2020GL092356

[14] Hosekova, L., Malila, M. P., Rogers, W. E., Roach, L. A., Eidam, E., Rainville, L., Kumar, N., and Thomson, J. (2020). Attenuation of ocean surface waves in pancake and frazil sea ice along the coast of the Chukchi Sea. Journal of Geophysical Research: Oceans, 125, e2020JC016746. https://doi.org/10.1029/2020JC016746

[13] Blanchard-Wrigglesworth, E., Roach, L. A., Donohoe, A., and Ding, Q. (2021). Impact of winds on Antarctic sea ice trends and variability. Journal of Climate, 1-47. https://doi.org/10.1175/JCLI-D-20-0386.1

[12] Kohout, A., Smith, M., Roach, L. A., Williams, G., Montiel, F., and Williams, M. (2020). Observations of exponential wave attenuation in Antarctic sea ice during the PIPERS campaign. Annals of Glaciology, 1-14. https://doi.org/10.1017/aog.2020.36

[11] Ackley, S. F., Stammerjohn, S., Maksym, T., Smith, M. M., Cassano, J., Guest, P., Tison, J.-L., Delille, B., Loose, B., Sedwick, P., DePace, L., Roach, L. A., and Parno, J. (2020). Sea ice production and air-ice-ocean-biogeochemistry interactions in the Ross Sea during the PIPERS 2017 autumn field campaign. Annals of Glaciology, 1-15. https://doi.org/10.1017/aog.2020.31

[10] Bracegirdle, T. J., Krinner, G., Tonelli, M., Haumann, F. M., Naughten, K. A., Rackow, T., Roach, L. A., and Wainer, I. (2020). Twenty first century changes in Antarctic and Southern Ocean surface climate in CMIP6. Atmospheric Science Letters, e984. https://doi.org/10.1002/asl.984

[9] Roach, L. A., Dörr J., Holmes, C. R., Massonnet, F., Blockley, E. W., Notz, D., Rackow, T., Raphael, M. N., O’Farrell, S. P., Bailey, D. A., and Bitz, C. M. (2020). Antarctic sea ice area in CMIP6. Geophysical Research Letters, 47, e2019GL086729. https://doi.org/10.1029/2019GL086729. [Download paper]. [Download Supplementary].

[8] Sea Ice Modelling Intercomparison Project Community [30 co-authors inc. Roach, L. A.] (2020). Arctic sea ice in CMIP6. Geophysical Research Letters, 47, e2019GL086749. https://doi.org/10.1029/2019GL086749

[7] Horvat, C., Flocco, D., Rees Jones, D. A., Roach, L. A., and Golden, K. M. (2020). The effect of melt pond geometry on the distribution of solar energy under first‐year sea ice. Geophysical Research Letters, 47. https://doi.org/10.1029/2019GL085956

[6] Roach, L. A., Bitz, C. M., Horvat, C., and Dean, S. M. (2019). Advances in modelling interactions between sea ice and ocean surface waves. Journal of Advances in Modeling Earth Systems, 11, 4167– 4181. https://doi.org/10.1029/2019MS001836

[5] Horvat, C., Roach, L. A., Tilling, R., Bitz, C. M., Fox-Kemper, B., Guider, C., Hill, K., Ridout, A., and Shepherd, A. (2019). Estimating the sea ice floe size distribution using satellite altimetry: theory, climatology, and model comparison. The Cryosphere, 13, 2869–2885. https://doi.org/10.5194/tc-13-2869-2019

[4] Roach, L. A., Horvat, C., Dean, S. M., and Bitz, C. M. (2018). An emergent sea ice floe size distribution in a global coupled ocean–sea ice model. Journal of Geophysical Research: Oceans, 123(6), 4322-4337. https://doi.org/10.1029/2017JC013692

[3] Roach, L. A., Smith, M. M., and Dean, S. M. (2018). Quantifying growth of pancake sea ice floes using images from drifting buoys. Journal of Geophysical Research: Oceans, 123(4), 2851-2866. https://doi.org/10.1002/2017JC013693

[2] Roach, L. A., Dean, S. M., and Renwick, J. A. (2018). Consistent biases in Antarctic sea ice concentration simulated by climate models. The Cryosphere, 12(1), 365-383. https://doi.org/10.5194/tc-12-365-2018

[1] Roach, L. A., Tett, S. F. B., Mineter, M. J., Yamazaki, K., and Rae, C. D. (2018). Automated parameter tuning applied to sea ice in a global climate model. Climate Dynamics, 50(1-2), 51-65. https://doi.org/10.1007/s00382-017-3581-5

Code & Data


I came across sea ice and climate science during an undergraduate degree in Mathematical Physics at the University of Edinburgh. My undergraduate research experience motivated me to do a PhD in sea ice modelling, at Victoria University of Wellington and NIWA in New Zealand. Following that, I moved to the US in 2019 for a postdoctoral appointment in the Ice Climate Group (led by Prof. Cecilia Bitz) at the University of Washington in Seattle.

  • 2021- Associate Research Scientist, NASA GISS and Columbia University, NYC, US
  • 2019-2021 Postdoc, Atmospheric Sciences, University of Washington, US
  • 2016-2019 Geophysics PhD, Victoria University of Wellington and NIWA, NZ
  • 2011-2015 Mathematical Physics MPhys, University of Edinburgh, UK


Feel free to reach out!