Active Projects

Title: Natural Climate Solutions for the United States
Principal Investigator:
Joe Fargione, Peter Ellis, Bronson Griscom (The Nature Conservancy)
Co-Principal Investigator:
Christopher A. Williams (Clark University)

Dr. Williams is involved in a scientific collaboration with The Nature Conservancy’s Science Director for North America focused on land management and land use solutions to mitigate climate change.  Williams’ team is providing detailed estimates of the carbon emissions that could be avoided by slowing or halting deforestation in the United States, along with high resolution maps of where forests are being lost and what they are being replaced by.  This work is soon to be published in a leading science journal.

Title: Translating Forest Change to Carbon Emissions/Removals Linking Disturbance Products, Biomass Maps, and Carbon Cycle Modeling in a Comprehensive Carbon Monitoring Framework
Principal Investigator: Christopher A. Williams (Clark University)
Co-Principal Investigators: G. James Collatz (NASA GSFC, Biospheric Sciences); Jeffrey G. Masek (NASA GSFC, Biospheric Sciences); Gretchen Moisen (US Forest Service)
Funding Source: NASA Carbon Monitoring System

Forests are a globally-significant store of carbon, but this store is vulnerable to release from disturbance processes such as harvesting or fires that oxidize forest carbon, releasing it to the atmosphere as CO2 and contributing to global warming. At the same time, intact forests serve as a major offset to rising CO2 concentrations as forest growth becomes stimulated by rising CO2 levels, enabling forests to absorb about one third of annual carbon emissions from fossil fuels and land use change. The balance of these processes is constantly changing and it varies widely from region to region. This project aims to quantify how much carbon is being released and taken up by each process over the entire United States, providing a new method for US reporting to the United Nations Framework Convention on Climate Change.

Historical forest clearing is responsible for about one third of all human-caused carbon emissions to date, with the rest coming from the combustion of fossil fuels. Avoiding further losses and protecting carbon uptake are both critical components of mitigating climate change. National and international policies aimed at protecting forest carbon storage rely heavily on high quality, accurate reporting (called “Tier 3”) that earns the greatest financial value of carbon credits and hence incentivizes forest conservation and protection. But methods for Tier 3 Measuring, Reporting, and Verification (MRV) are still in development.

This project will offer a new approach to Tier 3 MRV, involving a combination of direct remote sensing, ground based inventorying, and computer modeling methods to track forest carbon emissions and removals at a 1 km scale across the US. Few existing approaches seek to combine all of these sources of information. Another major advantage of our approach is its specificity about the underlying processes driving carbon flows. This enables the framework to be used as a decision support tool to help test the relative benefits of various land management strategies and to examine how today’s carbon sources and sinks will trend over time.


Title: Quantification of the regional impact of terrestrial processes on the carbon cycle using atmospheric inversions
Principal Investigator: Ken Davis (Penn State Atmospheric Sciences)
Co-Investigators: Christopher A. Williams (Clark University); G. James Collatz (NASA GSFC, Biospheric Sciences); Tristram West (Pacific Northwest National Lab); Stephen Ogle (Colorado State University Natural Resource Ecology Lab); Andrew Schuh (Colorado State University Atmospheric Sciences); Natasha Miles (PSU); Scott Richardson (PSU); Thomas Lauvaux (PSU); Martha Butler (PSU)
Funding Source: NASA Carbon Cycle Science

This project is examining the carbon balance of the southeastern US by adding new precision measurements of atmospheric CO2 concentrations in a regional network to inform advanced inverse modeling that can infer sinks and sources of carbon dioxide from measured concentrations in the atmosphere. This top-down approach will be combined with measurements and modeling of carbon fluxes from the ground up to examine consistency and explore possible biases in the various data sources.

Forests of the southeastern US are important for the North American carbon balance because the region is highly productive, is vigorously managed with intensive timber harvest, is sensitive to climate change, and is periodically inundated by severe storms that kill trees. The region also contains a pockets of intensive agricultural lands along with a range of urban and suburban hotspots of emissions. By combining a range of measurement and modeling approaches, this project will improve quantification of these carbon sources and sinks.


Title: Post-clearcut carbon, water, and energy fluxes and associated climate forcing
Principal Investigator: Christopher A. Williams (Clark University Geography)
Co-Investigators: Richard MacLean (Clark University Geography);
Funding Source: Clark University with additional support from NSF LTER through Harvard Forest

Ecological disturbances such as the clear cutting of forests are known to perturb ecosystem-atmosphere exchanges of water, carbon and energy in profound ways. However, the degree, character, and persistence of such perturbations are largely unknown but have important long-term implications for a host of ecosystem services such as carbon sequestration, wildlife habitat, and climate regulation. This project’s main objective is to quantify the full climate impacts of forest disturbances including the net ecosystem carbon balance, and energy and water forcings on atmospheric warming.

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Title: Attributing Regional Carbon Fluxes to Underlying Processes as part of RECCAP
Leads: Christopher A. Williams (Clark University Geography); Nicolas Gruber (ETH Zurich, Switzerland); Stephen Sitch (University of Exeter, UK); Pep Canadell (Global Carbon Project, Australia); Philippe Ciais (IPSL – LSCE – CEA – CNRS, France)
Funding Source: N/A

The international carbon cycle research community is undertaking its most ambitious effort ever to provide detailed regional understanding of the global carbon budget: the Regional Carbon Cycle Assessment and Processes initiative (RECCAP).  The primary goals are (1) to provide higher spatial resolution to analyses of the global carbon balance with the aim of improving the quantification and understanding of its drivers, and (2) to improve capacity for quantifying and monitoring the evolution of carbon fluxes at a regional to national level.  By assembling and comparing direct observations, model results, and atmospheric inversions, RECCAP is establishing the most comprehensive and detailed  carbon budgets ever produced for ten land and four ocean regions all using a common framework.

Professor Williams is leading one of five high-level syntheses seeking to explain the importance of different processes contributing to each region’s carbon balance.  Some of the processes being examined are enhanced plant growth from fertilization by elevated carbon dioxide and nitrogen, ozone inhibition of plant growth, effects of changes in sunlight quality and quantity, forest harvest and deforestation, and the changing climate (warming/cooling, wetting/drying).

Attribution is critically important because the future evolution of regional fluxes as well as the potential for carbon management as a climate mitigation option both depend on which mechanisms are contributing to the unexplained net carbon uptake taking place today.

Such a detailed and comprehensive attribution of the present day carbon balance has never before been attempted at a regional scale, or even globally.  With its interdisciplinary approach to using a wide range of information sources, the project is expected to build confidence in regional knowledge of carbon sources and sinks and reveal inconsistencies to guide the research agenda for the next decade. To learn more visit

Title: Albedo Trends Related to Land Cover Change and Disturbance: A Multi-sensor Approach
Principal Investigator: Jeffrey Masek (NASA GSFC Biospheric Sciences)
Co-Investigator: Feng Gao, Yanmin Shuai (Earth Resources Technology, Inc.)
Co-Is / Institutional PIs: Crystal Schaaf (Boston University Geography); Christopher A. Williams (Clark University Geography)
Funding Source: NASA The Science of Terra and Aqua

Numerous papers have highlighted how land-cover change and ecosystem disturbance can alter the surface energy balance through changes in albedo, surface roughness, and evapotranspiration. In some cases, these surface changes may constitute a larger radiative forcing than those arising from related carbon emissions. Past studies on post-disturbance albedo have been limited by the resolution of available MODIS data (500m), which is significantly coarser than the characteristic scales of ecosystem disturbance and human land use. Our project addresses this issue by creating high-resolution (30m) albedo maps through the fusion of Landsat TM/ETM+ directional reflectance with MODIS BRDF/Albedo (MCD43A) data. These maps permit trends in albedo to be evaluated at the characteristic scale of vegetation change (~1 ha).

Two algorithms are proposed to retrieve Landsat-resolution albedo: a “concurrent approach” which depends on overlapping MODIS and Landsat observations from the 2000-2010 period, and an “extended approach”, which uses an a priori BRDF table to extend retrievals back to the 1980’s. These fused products will be validated using in-situ Baseline Surface Radiation Network (BSRN) data. We will then evaluate the albedo trajectories for characteristic types of land cover conversion and disturbance across the globe. Specifically, we will (i) assemble a regional library of albedo values for IGBP land cover types; (ii) assemble time series of post-disturbance albedo from a latitudinal distribution of typical forest disturbance types (fire, insect damage, harvest); (iii) evaluate decadal trends in landscape albedo for “hotspots” of vegetation change; and (iv) assess the radiative forcing associated with historical (since 1700) and future (scenario-based) global land-cover change.

The outcome of the investigation will be an improved quantification of recent and historical albedo changes associated with land cover change and forest disturbance. Such information is needed to reduce uncertainties present in the current IPCC WG1 radiative forcing budget, and to forecast the effects of land management and land cover conversion on future climate.


Recently Completed Projects

Title: Impacts of Disturbance History on Carbon Fluxes and Stocks in North America
Principal Investigator: G. James Collatz (NASA GSFC, Biospheric Sciences)
Co-Principal Investigators: Jeffrey G. Masek (NASA GSFC, Biospheric Sciences), Christopher A. Williams (Clark University)
Funding Source: NASA Terrestrial Ecology

Forests of North America are thought to constitute a significant long term sink for atmospheric carbon but the relative importance of underlying mechanisms is poorly understood. This project seeks to clarify mechanisms and quantify spatial and temporal variability in forest carbon sinks. The work extends a previously NASA-funded project that involved the development of a new modeling framework characterizing carbon consequences of forest disturbance and regrowth based on Forest Inventory and Analysis (FIA) data and remote sensing (Landsat) of forest disturbances. Prior results quantify with greater certainty the regrowth carbon sink in the conterminous US, indicating that it is about half of what is generally quoted. This current research project continues to develop and advance the modeling framework by delving deeper into the mechanisms and intensity of documented disturbances using the improved NAFD products, the Monitoring Trends in Burn Severity fire data set, and forest insect damage data sets. In addition, we are engaged in a broader synthesis on the subject by integrating perspectives from flux towers, forest inventories, satellite remote sensing, ecosystem carbon modeling, and atmospheric inversions. We are exploring: (1) mechanistic attribution of forest carbon sinks to disturbance legacies versus growth enhancements; (2) spatial patterns of the continent’s process-specific sources and sinks; (3) interannual fluctuations in forest carbon sources and sinks; and (4) implications for managing forests to sequester carbon. From this new work we will provide more accurate estimates of the carbon fluxes and stocks and their implications on current and future atmospheric CO2 concentrations.


Title: Carbon Dioxide and Water Flux Response to Extreme Weather and Climate Anomalies: A Fluxnet Syntheses
Principal Investigator: Christopher Williams
Funding Agency: National Science Foundation

In this project researchers will perform a synthesis motivated by findings at individual flux tower sites that extreme weather and climate events (e.g., droughts, floods, hurricanes, and ice-storms) lead to pronounced and protracted anomalies in key components of the measured local carbon and water budgets. The PIs will assess the degree of commonality across flux tower sites in the response of the ecosystem to extreme events, derive a coherent description of these responses, and use remote sensing data to extrapolate spatially coherent and persistent impacts on ecosystems, specifically on vegetation, that subsequently may impact carbon and water balances and climate trajectories on a larger spatial scale. The PIs will also assess the ability of land surface models spanning a wide range of complexity to simulate the observed response of terrestrial state variables and fluxes to extreme events when driven by observed meteorology. The project is composed entirely of a team of early-career scientists.

This work is supported under the NSF Carbon and Water in the Earth System solicitation, an interdisciplinary funding opportunity from the Directorate of Geosciences.