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Impact of Emissions, Chemistry, and Climate on Atmospheric Carbon Monoxide: 100-year Predictions from a Global Chemistry-Climate Model

The possible trends for atmospheric carbon monoxide in the next 100 yr have been illustrated using a coupled atmospheric chemistry and climate model driven by emissions predicted by a global economic development model. Various model runs with different assumptions regarding emissions or model parameters have been carried out to investigate the impacts of model and emission uncertainties on the predictions. We have found complicated interactions among emissions, atmospheric chemistry, and climate regarding the distributions and evolution of CO in the atmosphere. Based on the predicted emissions of methane and carbon monoxide, the model predicts an increasing trend of carbon monoxide in the next century with a tropospheric mole fraction of CO in 2100 double its present-day value. Methane emissions are found to have the most important effect on the future atmospheric CO budget. High methane emissions cause significant depletion of tropospheric OH, increase of CO concentrations, and lengthening of lifetimes of many chemical species including CO and CH4. The global average atmospheric lifetime of CO is predicted in our reference model run to be about 0.6 month longer than its present value (~2 months). The predicted emissions of CO increase only slightly over the next century, so the impact of CO emissions on the predicted CO abundance appears to be less important than that of methane. Consequently, maintaining the emissions of CH4 at their current levels can prevent significant future changes in tropospheric chemistry, while similar controlling emissions of CO cannot achieve the same result. This study also indicates that climate variations, especially those causing changes in H2O concentrations, can influence atmospheric trends of carbon monoxide. A two-way interaction between chemistry and climate regarding CO is evident. Specifically, the budget of atmospheric CO affects the destruction of methane and the production of CO2, ozone, and sulfate aerosols and thus affects climate, while the resultant changes in climate modify the budget of CO-CH4 in turn through their effects on H2O and temperature.

Impact of Sulfur and Carbonaceous Emissions from International Shipping on Aerosol Distributions and Direct Radiative Forcing

We describe in this report an effort using the MIT/NCAR three-dimensional aerosol-climate model to study the impact of ship emissions on chemical composition and radiative forcing of aerosols. Our results indicate that international shipping can be a non-negligible factor in determining the radiative forcing of aerosols over specific regions with intensive ship activities. These places include the European, eastern Asian, and American coastal regions. The global mean aerosol radiative forcing caused by the ship emissions ranges from -12.5 to -23 mW/m2, depending on whether the mixing between black carbon and sulfate is included in the model. However, over the aforementioned places, the radiative forcing resulting from ship emissions can be much more important in the total regional aerosol forcing.

Impacts of Greenhouse Gas Mitigation Policies on Agricultural Land

Greenhouse gas (GHG) emissions are widely acknowledged to be responsible for much of the global warming in the past century. A number of approaches have been proposed to mitigate GHG emissions. Since the burning of fossil-based fuels is an important source of GHGs, the policies on GHG-mitigation encourage the replacement of fossil-based energy with biomass energy. However, a large-scale development of biomass energy may lead to changes in agricultural land use, which are important sources of GHG emissions, and therefore undermine the effectiveness of GHG-mitigation policies. In this research, I analyze the impacts of GHG-mitigation policies on five types of agricultural land (cropland, managed forestry land, pasture land, un-managed forestry land, and un-managed grassland) as well as carbon stored in such land during the 21st century. The scholars in the MIT Joint Program of Science and Policy on Global Change use the Integrated Global Systems Model (IGSM) to simulate changes in climate in response to GHG-mitigation policies, while the researchers at the U. S. Marine Biological Laboratory (MBL) apply the Terrestrial Ecosystem Model (TEM) to simulate land productivities. Based on the predictions of land characteristics affecting land-use decisions, I develop an econometric model to predict the land use affected by climate, GHGs, and tropospheric ozone at the grid-cell scale of 0.5 * 0.5 longitude by latitude. I use the Emissions Prediction and Policy Analysis (EPPA) model to capture the regional land use driven by economic forces. Then, I develop the downscaling methods to link these two land-use effects. I conduct this research in two scenarios: in the baseline, I assume that there are no policies to mitigate GHG emissions during the 21st century; in the policy scenario, I assume that there are specific policies to limit GHG emissions during the 21st century. I confirm the hypothesis that biomass-energy production would lead to the conversion of the five types of agricultural land, and the carbon stored in such land would decrease; the GHG-mitigation policies, leading to more production of biomass energy and conversion of agricultural land, would cause an even more severe loss of the carbon stored in agricultural land. Although the GHG-mitigation policies would generally reduce the atmospheric GHG emissions by using more energy from biomass, such endeavors would be partly counteracted by the landuse conversion as a result of large-scale production of biomass energy.

Impacts of Meteorology-Driven Seed Dispersal on Plant Migration: Implications for Future Vegetation Structure under Changing Climates

As the impacts between land cover change, future climates and ecosystems are expected to be substantial (e.g., Feddema et al., 2005), there are growing needs for improving the capability of simulating the global vegetation structure and landscape as accurate as possible. In order to serve these needs, Dynamic Global Vegetation Models (DGVMs) are used to describe the current status of vegetation structure and biogeography as well as estimate their future states, either with prescribed climates or coupled to climate models. Yet, current DGVMs assume ubiquitous availability of seeds and do not consider any seed dispersal mechanisms and/or plant migration process, which may influence the assessment of impacts to the ecosystem that rely on the vegetation structure changes (i.e., change in albedo, runoff, and terrestrial carbon sequestration capacity). For the first time, this study incorporates time-varying wind-driven seed dispersion (i.e., the SEED configuration) as a dynamic constraint to the migration process of natural vegetation in the Community Land Model (CLM)-DGVM.

Compared to the satellite-derived tree covers, the result shows significantly improved representation of vegetation in regions such as boreal forests in Western Siberia and temperate forests in Eastern Europe. The prevailing wind pattern, along with the existing vegetation structure in nearby grid cells, alters the competition dynamics of the trees in these regions by filtering unrealistic saplings out and adjusting their establishment rates.

The SEED configuration is then applied to project future vegetation structures under two climate mitigation scenarios (No-policy vs. 450ppm CO2 stabilization) for the 21st century. The results indicate that regional changes of vegetation structure under changing climates are expected to be significant. In the high latitudes, regions such as Alaska and Siberia are expected to experience substantial shifts of forestry structure, characterized by expansion of needle-leaf boreal forest and shrinkage of C3 grass Arctic. In the mid-latitudes, temperate trees are likely to expand in South America, South Africa, and East Asia, showing sensitive responses to changing climates for the latter part of the 21st century. In Tropics, a most notable degree of change in the composition of tropical trees and C4 grass are projected in Amazon and also regions in Africa.

The vulnerability assessment suggested by this study shows that vegetation structures in Alaska, Greenland, Central America, southern part of South America, East Africa and East Asia are susceptible to changing climates, regardless of the two climate mitigation scenarios. Regions such as Greenland, Tibet, South Asia and Northern Australia, however, may substantially alleviate their risks of rapid change in vegetation structure, given a robust greenhouse gas stabilization target.

The impacts of future vegetation change on radiation budget cannot be neglected. The results suggest that depending upon the climate mitigation scenarios, the vegetation change may accelerate or offset the anticipated warming trend of the 21st century. Proliferation of boreal forests in the high latitudes is expected to amplify the warming trend (i.e., a positive feedback to climate), if no mitigation policy is implemented. In contrast, under the 450ppm scenario, vegetation structure may buffer the warming trend, which is a negative feedback to climate. A series of hydrologic processes including interception of rainfall by forest canopy, evapotranspiration, and runoff are to be influenced by the modified vegetation structures. The magnitude of the runoff response by the vegetation change may not exceed the direct response from hydro-climate change; however, the spatial pattern of runoff change due to vegetation indicates that vegetation change may offset or be complementary to increase in runoff due to enhanced precipitation under climate warming. Reduction of terrestrial productivity and a conservative estimate of vegetation carbon storage (-8PgC/yr and 24PgC, respectively under the NP scenario) in the 21st century may be due to ignoring the CO2 fertilization effect and partially applying the new SEED configuration to project future vegetation structures.

The newly developed SEED configuration may serve to attain more comprehensive representations of future vegetation structures and thus assess the impacts of natural vegetation distribution on the ecosystems. The results may also be used as indicators of assessing vulnerabilities in providing ecosystem goods and services.

Impacts of Ozone on Trees and Crops

In this review article, we explore how surface-level ozone affects trees and crops with special emphasis on consequences for productivity and carbon sequestration. Vegetation exposure to ozone reduces photosynthesis, growth, and other plant functions. Ozone formation in the atmosphere is a product of NOx, which are also a source of nitrogen deposition. Reduced carbon sequestration of temperate forests resulting from ozone is likely offset by increased carbon sequestration from nitrogen fertilization. However, since fertilized croplands are generally not nitrogen-limited, capping ozone-polluting substances in the USA, Europe, and China can reduce future crop yield loss substantially.

Implementation of a Cloud Radiative Adjustment Method to Change the Climate Sensitivity of CAM3

Conducting probabilistic climate projections with a particular climate model requires the ability to vary the model’s characteristics, such as its climate sensitivity. In this study, we implement and validate a method to change the climate sensitivity of the National Center for Atmospheric Research (NCAR) Community Atmosphere Model version 3 (CAM3) through a cloud radiative adjustment. Results show that the cloud radiative adjustment method does not lead to physically unrealistic changes in the model’s response to an external forcing, such as doubling CO2 concentrations or increasing sulfate aerosol concentrations. Furthermore, this method has some advantages compared to the traditional perturbed physics approach. In particular, the cloud radiative adjustment method can produce any value of climate sensitivity within the wide range of uncertainty based on the observed 20th century climate change. As a consequence, this method allows Monte Carlo type probabilistic climate forecasts to be conducted where values of uncertain parameters not only cover the whole uncertainty range, but cover it homogeneously. Unlike the perturbed physics approach which can produce several versions of a model with the same climate sensitivity but with very different regional patterns of change, the cloud radiative adjustment method can only produce one version of the model with a specific climate sensitivity. As such, a limitation of this method is that it cannot cover the full uncertainty in regional patterns of climate change.

Implications of ozone on carbon sequestration and climate policy in the U.S. using the MIT Integrated Global Systems Model

Exposure of plants to ozone inhibits photosynthesis and therefore reduces vegetation production and carbon sequestration. The damaging effects of tropospheric ozone vary spatially because human activities responsible for the emissions of ozone precursors are highly concentrated in urban and industrial centers. We developed scenarios of ozone-precursor emissions and the resultant ozone concentrations using the MIT Integrated Global Systems Model (IGSM) through the year 2100 and explored the consequent effects on terrestrial ecosystems using the Terrestrial Ecosystem Model (TEM). We then used the Emissions Prediction and Policy Analysis (EPPA) model, a component of the IGSM, to evaluate the cost of increased mitigation efforts required to offset lost carbon sequestration. We considered both a global climate policy that limits future greenhouse gas (GHG) emissions and an air quality policy that limits pollutant emissions to their 1995 levels in the developed countries. We also considered agricultural management that includes optimal irrigation and fertilization and no irrigation and fertilization for croplands. We found that the loss of carbon sequestration in the U.S. at the end of the 21st century due to ozone pollution ranged from negligible to as much as 0.3 PgC yr$^{-1}$ depending upon the policy options pursued. We valued these reductions in terms of the change in the net present value of the cost to the U.S. through 2100 of a global carbon policy designed to approximately stabilize atmospheric CO$_{2}$ levels at 550 ppm. For the U.S., failure to consider ozone damages to vegetation would by itself raise the costs over the next century of stabilizing atmospheric concentrations of CO$_{2}$ by 11 to 19% (\$0.3 to \$0.6 trillion) because emissions from fossil fuels will need to be reduced more to compensate for the reduced carbon sequestration by terrestrial ecosystems. With a pollution cap, damages are reduced to 6 to 12% (\$0.2 to \$0.3 trillion) of the total cost. However, climate policy that reduces fossil fuel use and methane emissions would also reduce the emissions of the ozone precursors and therefore, ozone concentrations and ozone damages. The savings in reduced carbon emissions reductions costs are estimated to be between 1 and 17% (\$0.09 to \$0.3 trillion) of the cost of the climate policy. The cost estimates are sensitive to the assumed 5% discount rate and the details of the climate policy and how the burden is allocated among countries. Tropospheric ozone effects on terrestrial ecosystems produce a surprisingly large feedback in estimating climate policy costs that, heretofore, has not been included in cost estimates.

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

The effects of various aspects of global change (e.g., climate change, changes in the chemistry of the atmosphere, such as CO2 and O3, and land-use change) on the hydrologic cycle are becoming an important research area. For example, with respect to increases in atmospheric CO2, recent work supports the contention that there will be reduced evapotranspiration and therefore increased water availability in a CO2-rich world. Our new research on this topic suggests that various aspects of global change combine to affect hydrology in terrestrial ecosystems, and that it is particularly important to include carbon-nitrogen interactions in these studies. We have developed a new version of the Terrestrial Ecosystems Model (TEM) to examine the effects of carbon-nitrogen interactions on the water cycle. This new version includes explicit modeling of the stomatal exchange of CO2 and water, as well as a new approach to carbon and nitrogen allocation in plants. Using this new version of TEM, we have performed a range of site-level and regional experiments across the eastern United States. For example, using data from Harvard Forest, MA, a predominantly deciduous mixed forest, we ran two transient simulations from 1700 to 2100, with and without considering nitrogen limitations on plant productivity. In both of these simulations, we allowed CO2 to double by 2100, but maintained present-day climate. In these two experiments, we found that runoff increased through the 21st century in response to elevated atmospheric CO2. Without nitrogen limitation on plant productivity, the increase in runoff was 12%. However, with nitrogen limitation on plant productivity, the increase in runoff nearly doubled to 21%. This difference in runoff response was the result of a stronger transpiration reduction associated with a smaller increase in photosynthesis in the nitrogen limitation case. In this resentation we will discuss a set of site-level and regional experiments that explore the effects of carbon-nitrogen interactions on the water cycle in the context of different combinations of global changes including climate changes, changes in nitrogen deposition, and changes in tropospheric ozone. Since the carbon and water cycles are tightly coupled, future considerations of ecohydrology must take into account carbon-nitrogen interactions and other multiple stresses that strongly influence the carbon cycle.

© 2009 by the American Geophysical Union

Improving the Refining Sector in EPPA

The MIT Emissions Prediction and Policy Analysis (EPPA) model is a recursive-dynamic multi-regional general equilibrium model of the world economy, which is built on the GTAP5 dataset and additional data for the greenhouse gas and urban gas emissions. The GTAP5 dataset aggregates all the different types of petroleum products, from transportation fuels to refinery residues, in the same "refined oil" commodity. We augment the GTAP supply, demand, and trade data in order to disaggregate the refined oil commodity into six different categories of petroleum products, each with its specific uses and associated emission factors. We then expand the EPPA model accordingly, and improve its representation of the oil industry by introducing new upstream and downstream oil technologies and taking into account the changes in the crude mix. This work opens the door to future in-depth analyses of how supply and demand for refined products could be affected by climate policy.

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