Gretchen Keppel-Aleks

Carbon Cycle Research Group

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Our research group is interested in understanding links between the climate system and the carbon cycle

How will carbon sinks in the ocean and terrestrial ecosystems interact with changing atmospheric composition and climate?

How can we best use atmospheric and remote sensing observations to improve our ability to predict the evolution of the climate system on timescales of decades to centuries?

How can we employ remote sensing observations to understand global biogeochemistry?

How will human activity interact with longer term climate changes to affect the carbon cycle?

Remote sensing observations for carbon cycle science

Remote sensing observations of atmospheric composition and land surface processes provide global information about the Earth system. Our group employs novel analysis methodology to harness these observations towards understanding underlying ecosystem processes and for testing insights from these observations againt models. We use total column observations from the TCCON network, and observations of CO2, CH4, and Chlorophyll fluorescence from from NASA's OCO-2 satellite and Japan's . GOSAT satellite to understand global carbon dynamics. More recently, we have gotten involved in NASA's Soil Moisture Active Passive (SMAP) mission to link the carbon, water and energy cycles.

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CO2 absorption spectrum measured by ground-based Fourier Transform Spectrometry

Using short term variability to estimate long-term carbon-climte feedbacks

Almost 50% of human-emitted CO2 is taken up by the oceans or terrestrial ecosystems, although interannual varibility in climate can cause short term changes in the fraction of CO2 that remains in the atmosphere. We are investigating links between observed changes in the atmospheric CO2 growthrate, climate drivers such as temperature and precipitation, and fire -- which is controlled both by climate and by human land use and land management decisions. Using both simple models with generalized surface fluxes and Earth system models, we are determining where climate-carbon feedbacks are robust and may be good predictors of long-term evolution and where more observations are needed to disentangle climate effects.

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Interannual variability in atmospheric CO2 measured by NOAA's cooperative flask sampling network

Benchmarking Earth system models against atmospheric observations

Earth system models (ESMs) predict the evolution of atmospheric CO2 concentrations based on feedbacks in ocean- and terrestrial ecosystem- carbon storage as climate evolves, tackling one of the biggest uncertainties in the extent of global climate change for a given anthropogenic emissions trajectory. We develop rigorous ways to analyze output from these models against different types of observations to determine model performance on seasonal, interannual, and decadal timeseries. We also work with the Community Earth System Model (CESM), a fully coupled model, to simulate future climate-carbon interactions.

Atmospheric Tracer Transport

Fluxes of carbon, water vapor, and energy between the surface and the atmosphere are all linked. Energy fluxes at the surface help determine the vertical structure of the atmosphere, which in turn impacts our interpretation of atmospheric carbon observations. Our group seeks to understand better how to improve vertical mixing and tracer transport parameterizations so that we can better use models for interpreting atmospheric observations. We are further interested in understanding how changing atmospheric dynamics will affect -- and be affected by -- changing terrestrial ecosystems.