Are Land-use Emissions Scalable with Increasing Corn Ethanol Mandates in the United States?

In response to the Renewable Fuel Standard, the U.S. transportation sector now consumes a substantial amount (13.3 billion gallons in 2010) of ethanol. A key motivation for these mandates is to expand the consumption of biofuels in road transportation to both reduce foreign oil dependency and to reduce greenhouse gas (GHG) emissions from the consumption of fossil fuels in transportation. In this paper, we present the impacts of several biofuels expansion scenarios for the U.S. in which scaled increases in the U.S. corn ethanol mandates are modeled to explore the scalability of GHG impacts. The impacts show both expected and surprising results. As expected, the area of land used to grow biofuel crops increases with the size of the policy in the U.S., and some land-use changes occur abroad due to trade in agricultural commodities. Because the land-use changes happen largely in the U.S., there is an increase in U.S. land-use emissions when natural lands are converted to agricultural use in the policy scenarios. Further, the emissions impacts in the U.S. and the rest of the world in these scenarios, including land-use emissions, scale in direct proportion to the size of the U.S. corn ethanol mandates. On the other hand, the land-use emissions that occur in the rest of the world are disproportionately larger per hectare of change due to conversions of more carbon-rich forests to cultivate crops and feed livestock.We gratefully acknowledge the financial support for this work from the U.S. Department of Energy, Office of Science under DE-FG02-94ER61937, the U.S. Environmental Protection Agency under XA-83600001-1 and XA-835055101-2, and other government, industry, and foundation sponsors of the Joint Program on the Science and Policy of Global Change

Interactions between carbon and nitrogen dynamics in estimating net primary productivity for potential vegetation in North America

We use the terrestrial ecosystem model (TEM), a process-based model, to investigate how interactions between carbon (C) and nitrogen (N) dynamics affect predictions of net primary productivity (NPP) for potential vegetation in North America. Data on pool sizes and fluxes of C and N from intensively studied field sites are used to calibrate the model for each of 17 non-wetland vegetation types. We use information on climate, soils, and vegetation to make estimates for each of 11,299 non-wetland, 0.5° latitude × 0.5° longitude, grid cells in North America. The potential annual NPP and net N mineralization (NETNMIN) of North America are estimated to be 7.032 × 1015 g C yr−1 and 104.6 × 1012 g N yr−1, respectively. Both NPP and NETNMIN increase along gradients of increasing temperature and moisture in northern and temperate regions of the continent, respectively. Nitrogen limitation of productivity is weak in tropical forests, increasingly stronger in temperate and boreal forests, and very strong in tundra ecosystems. The degree to which productivity is limited by the availability of N also varies within ecosystems. Thus spatial resolution in estimating exchanges of C between the atmosphere and the terrestrial biosphere is improved by modeling the linkage between C and N dynamics. We also perform a factorial experiment with TEM on temperate mixed forest in North America to evaluate the importance of considering interactions between C and N dynamics in the response of NPP to an elevated temperature of 2°C. With the C cycle uncoupled from the N cycle, NPP decreases primarily because of higher plant respiration. However, with the C and N cycles coupled, NPP increases because productivity that is due to increased N availability more than offsets the higher costs of plant respiration. Thus, to investigate how global change will affect biosphere-atmosphere interactions, process-based models need to consider linkages between the C and N cycles

Green House Gas Mitigation Policy, Bio-fuels and Land-use Change- a Dynamic Analysis

Research and Development/Tech Change/Emerging Technologies, Resource /Energy Economics and Policy,

Insights and issues with simulating terrestrial DOC loading of Arctic river networks

Author Posting. © Ecological Society of America, 2013. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 23 (2013): 1817-1836, doi:10.1890/11-1050.1.Terrestrial carbon dynamics influence the contribution of dissolved organic carbon (DOC) to river networks in addition to hydrology. In this study, we use a biogeochemical process model to simulate the lateral transfer of DOC from land to the Arctic Ocean via riverine transport. We estimate that, over the 20th century, the pan-Arctic watershed has contributed, on average, 32 Tg C/yr of DOC to river networks emptying into the Arctic Ocean with most of the DOC coming from the extensive area of boreal deciduous needle-leaved forests and forested wetlands in Eurasian watersheds. We also estimate that the rate of terrestrial DOC loading has been increasing by 0.037 Tg C/yr2 over the 20th century primarily as a result of climate-induced increases in water yield. These increases have been offset by decreases in terrestrial DOC loading caused by wildfires. Other environmental factors (CO2 fertilization, ozone pollution, atmospheric nitrogen deposition, timber harvest, agriculture) are estimated to have relatively small effects on terrestrial DOC loading to Arctic rivers. The effects of the various environmental factors on terrestrial carbon dynamics have both offset and enhanced concurrent effects on hydrology to influence terrestrial DOC loading and may be changing the relative importance of terrestrial carbon dynamics on this carbon flux. Improvements in simulating terrestrial DOC loading to pan-Arctic rivers in the future will require better information on the production and consumption of DOC within the soil profile, the transfer of DOC from land to headwater streams, the spatial distribution of precipitation and its temporal trends, carbon dynamics of larch-dominated ecosystems in eastern Siberia, and the role of industrial organic effluents on carbon budgets of rivers in western Russia.This study was supported, in part, by the U.S. National Science Foundation under grants ARC-0531047, ARC-0531082, ARC-0531119, ARC-0554811, and ARC- 0652838; the U.S. Environmental Protection Agency under grant R833261; the U.S. Department of Energy under grant DE-FG02-08ER64597; and the U.S. National Aeronautics and Space Administration under grant NNX09A126G

Nitrogen attenuation of terrestrial carbon cycle response to global environmental factors

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 23 (2009): GB4028, doi:10.1029/2009GB003519.Nitrogen cycle dynamics have the capacity to attenuate the magnitude of global terrestrial carbon sinks and sources driven by CO2 fertilization and changes in climate. In this study, two versions of the terrestrial carbon and nitrogen cycle components of the Integrated Science Assessment Model (ISAM) are used to evaluate how variation in nitrogen availability influences terrestrial carbon sinks and sources in response to changes over the 20th century in global environmental factors including atmospheric CO2 concentration, nitrogen inputs, temperature, precipitation and land use. The two versions of ISAM vary in their treatment of nitrogen availability: ISAM-NC has a terrestrial carbon cycle model coupled to a fully dynamic nitrogen cycle while ISAM-C has an identical carbon cycle model but nitrogen availability is always in sufficient supply. Overall, the two versions of the model estimate approximately the same amount of global mean carbon uptake over the 20th century. However, comparisons of results of ISAM-NC relative to ISAM-C reveal that nitrogen dynamics: (1) reduced the 1990s carbon sink associated with increasing atmospheric CO2 by 0.53 PgC yr−1 (1 Pg = 1015g), (2) reduced the 1990s carbon source associated with changes in temperature and precipitation of 0.34 PgC yr−1 in the 1990s, (3) an enhanced sink associated with nitrogen inputs by 0.26 PgC yr−1, and (4) enhanced the 1990s carbon source associated with changes in land use by 0.08 PgC yr−1 in the 1990s. These effects of nitrogen limitation influenced the spatial distribution of the estimated exchange of CO2 with greater sink activity in high latitudes associated with climate effects and a smaller sink of CO2 in the southeastern United States caused by N limitation associated with both CO2 fertilization and forest regrowth. These results indicate that the dynamics of nitrogen availability are important to consider in assessing the spatial distribution and temporal dynamics of terrestrial carbon sources and sinks.We also acknowledge the financial support of the National Aeronautics and Space Administration Land Cover and Land Use Change Program (NNX08AK75G)

Land carbon sequestration within the conterminous United States : regional- and state-level analyses

Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 120 (2015): 379–398, doi:10.1002/2014JG002818.A quantitative understanding of the rate at which land ecosystems are sequestering or losing carbon at national-, regional-, and state-level scales is needed to develop policies to mitigate climate change. In this study, a new improved historical land use and land cover change data set is developed and combined with a process-based ecosystem model to estimate carbon sources and sinks in land ecosystems of the conterminous United States for the contemporary period of 2001–2005 and over the last three centuries. We estimate that land ecosystems in the conterminous United States sequestered 323 Tg C yr−1 at the beginning of the 21st century with forests accounting for 97% of this sink. This land carbon sink varied substantially across the conterminous United States, with the largest sinks occurring in the Southeast. Land sinks are large enough to completely compensate fossil fuel emissions in Maine and Mississippi, but nationally, carbon sinks compensate for only 20% of U.S. fossil fuel emissions. We find that regions that are currently large carbon sinks (e.g., Southeast) tend to have been large carbon sources over the longer historical period. Both the land use history and fate of harvested products can be important in determining a region's overall impact on the atmospheric carbon budget. While there are numerous options for reducing fossil fuels (e.g., increase efficiency and displacement by renewable resources), new land management opportunities for sequestering carbon need to be explored. Opportunities include reforestation and managing forest age structure. These opportunities will vary from state to state and over time across the United States.This work was supported by NSF grants 104918, 1137306, and 1237491; EPA grant XA-83600001-1; and DOE grant DE-FG02-94ER61937.2015-08-2

Correction to “Importance of carbon-nitrogen interactions and ozone on ecosystem hydrology during the 21st century”

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 114 (2009): G03009, doi:10.1029/2009JG001083

Future nitrogen availability and its effect on carbon sequestration in Northern Eurasia

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Kicklighter, D. W., Melillo, J. M., Monier, E., Sokolov, A. P., & Zhuang, Q. Future nitrogen availability and its effect on carbon sequestration in Northern Eurasia. Nature Communications, 10, (2019): 3024, doi: 10.1038/s41467-019-10944-0.Nitrogen (N) availability exerts strong control on carbon storage in the forests of Northern Eurasia. Here, using a process-based model, we explore how three factors that alter N availability—permafrost degradation, atmospheric N deposition, and the abandonment of agricultural land to forest regrowth (land-use legacy)—affect carbon storage in the region’s forest vegetation over the 21st century within the context of two IPCC global-change scenarios (RCPs 4.5 and 8.5). For RCP4.5, enhanced N availability results in increased tree carbon storage of 27.8 Pg C, with land-use legacy being the most important factor. For RCP8.5, enhanced N availability results in increased carbon storage in trees of 13.4 Pg C, with permafrost degradation being the most important factor. Our analysis reveals complex spatial and temporal patterns of regional carbon storage. This study underscores the importance of considering carbon-nitrogen interactions when assessing regional and sub-regional impacts of global change policies.This research was supported by the US National Aeronautics and Space Administration (NASA) Land-Cover and Land-Use Change (LCLUC) Program grant NNX14AD91G. The Joint Program on the Science and Policy of Global Change is funded by a number of federal agencies and a consortium of 40 industrial and foundation sponsor (for the complete list see http://globalchange.mit.edu/sponsors)