Greenhouse gas (GHG) emissions are widely acknowledged to be responsible for much of the global warming in the past century. 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. This policy would lead to a large-scale conversion of land to production of crops for biomass energy. The impacts of GHG mitigation policies were analyzed for five types of agricultural land—cropland, managed forestry, pasture, unmanaged forestry, and unmanaged grassland—in terms of their carbon storage capacities and the effects of conversion of the land to use for biomass fuel cropland. The research indicates that biomass energy production would lead to a reduction of the biological carbon-storage capacities of these land types. Although there would still be a net benefit in reducing atmospheric GHG emissions, such benefits would be partly counteracted by the land-use conversion. Thus, this paper provides an example of the need for further study to discern all the implications of proposed GHG mitigation policies and technologies and the degrees to which they are likely to enhance our future.
One of the most debated topics today is global climate change, and greenhouse gas (GHG) emissions are widely acknowledged to be responsible for much of the global temperature increases observed in the past century. Aiming at mitigating GHG emissions, most national governments have signed and ratified the Kyoto Protocol, a treaty ratifying the United Nations Framework Convention on Climate Change (UNFCCC) with the objective of reducing GHG emissions.
As of June 2007, 172 nations have ratified the Kyoto Protocol, and among them are thirty-six countries and the European Union required to reduce GHG emissions to certain levels specified for each of them in the treaty. The U.S. government, although having not ratified this agreement yet, is also considering a number of approaches to mitigate GHG emissions.
Since the burning of conventional fossil-based fuels is an important source of GHGs, the policies for mitigation encourage the replacement of fossil-based energy with biomass energy. Most commonly, biomass refers to plant matter grown for conversion into and use as biofuel mainly in the form of ethanol. Biomass is grown from several plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sugarcane, and oil palm (palm oil). The net effect of ethanol burning on GHG emissions would be close to zero.
The net zero emissions from biofuels are possible since the raw material (feedstock, switchgrass, sugarcane, and forestry residues) used to fuel the production captures the carbon dioxide through photosynthesis during its growth, as the energy used to produce and process the fuel from the raw material is also expected to have its origins in organic resources. As an example, the production and use of ethanol from sugarcane releases very low net emissions of carbon dioxide since the energy necessary to transform sugarcane in ethanol comes mostly from the sugarcane agricultural resources.
The research described in this paper is a small part of the work performed within the context of extensive studies by other numerous prominent researchers at the Massachusetts Institute of Technology (MIT). This paper primarily only considers the impacts of the GHG mitigation policies for biomass crop production and land use. The various MIT efforts and numerical models are described here for context, and credit has to be attributed to others for those models.
Large-Scale Implications
A large-scale development of biomass energy may lead to very significant regional and global land-use changes (the deforestation in Brazil is one such example) that then results in a net decrease in the capacity of the land and its biological components to absorb and be a sink for GHGs, and therefore potentially undermining the effectiveness of the GHG mitigation policies. Unfortunately, there is a lack of knowledge of the potentials and limitations of a worldwide development of biomass energy production, and the resultant land-use effects were not included in the policy decisions on GHG mitigation.
In the research described here, the impacts of the GHG mitigation policies for biomass crop production were considered in terms of usage and conversion from five types of agricultural land—cropland, managed forestry land, pasture land, unmanaged forestry land, and unmanaged grassland. The impacts include land use, land rent, and the possible feedbacks to the carbon stored in such land. Such impacts may vary from place to place because of the differences in climate, soil, or the way the policies are adopted. This research was conducted within the framework of the MIT Integrated Global Systems Model (IGSM), which includes submodels of the relevant aspects of the natural earth system coupled to a model of the human component interacting with climate processes.
MIT Climate Models
Projections of climate change have been hampered by our abilities to model the complex impacts between the human and climate systems. An important factor leading to this limitation is the significant uncertainties in climate system properties. Another difficulty lies in the “century-scale” nature of the projection: it is difficult to project emissions of GHGs and possible land-use changes over a long horizon because of the uncertainties in population growth, economic development, technological evolution, etc. Because of these limitations, existing general circulation models (GCMs) that couple atmosphere-ocean-land components differ significantly in projections of climate change. Considering such limitations of existing climate models, it is necessary to quantify the uncertainties in projections of climate change.
The Joint Program of Science and Policy on Global Climate Change was founded at MIT in 1991 as an interdisciplinary organization that conducts research, independent policy analysis, and public communication on issues of global environmental change. The program’s work is focused on the integration of natural and social science aspects of the climate issue to produce analyses relevant to ongoing national and international discussions. It is designed to develop annual projections of economic growth and anthropogenic emissions of greenhouse-related gases and aerosols. This program has led to the development of several numerical and economic models (described below).
The MIT IGSM is designed for analyzing the global environmental changes that may result from anthropogenic causes, quantifying the uncertainties associated with the projected changes, and assessing the costs and environmental effectiveness of proposed policies to mitigate climate risk. The climate system component of the IGSM is designed to provide the flexibility required to handle multiple uncertainty analyses and policy studies while representing in the best way possible the physics, chemistry, and biology components. In addition, the earth system component of the IGSM is linked to a model of human impacts in order to include the impacts between humans and climate change into the climate projections.
Specifically, the MIT IGSM includes an economic model for analysis of GHGs and aerosol precursor emissions and mitigation proposals, a coupled atmosphere-ocean-land surface model, and models of natural ecosystems. The major model components of the IGSM include:
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A model of human activities and emissions (the Emission Prediction and Policy Analysis or the EPPA model);
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An atmospheric dynamics, physics and chemistry model, which includes a submodel of urban chemistry;
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An ocean model with carbon cycle and sea ice submodels; and
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A linked set of coupled land models–the Terrestrial Ecosystem Model (TEM), the Natural Emissions Model (NEM), and the Community Land Model (CLM). These models encompass the global terrestrial water and energy budgets as well as terrestrial ecosystem processes.
By mitigating GHG atmospheric concentrations, the GHG mitigation policies also lead to changes in climate conditions, air temperature, and precipitation for instance. In addition, such policies reduce some pollutant gases from fossil fuel burning (NOx for example), and these gases are important precursors of tropospheric ozone. It was possible to examine the combined effects of changes in climate, GHG concentrations, and tropospheric ozone levels.
To the extent that land productivities are affected by climate, GHGs, and tropospheric ozone, there may be important economic consequences. To make possible a comprehensive analysis of the land-use effects of GHG mitigation policies, we link the impacts of economic forces at the regional scale used in a computable general equilibrium model of the world economy with the feedbacks of climate, GHGs, and tropospheric ozone at the grid-cell scale used in a biophysical model of global terrestrial ecosystems—EPPA) model and TEM.
The EPPA model was developed by the MIT Joint Program of Science and Policy on Global Change. Based at the regional scale, the EPPA model simulates the economy through time to produce scenarios of GHGs, aerosols, other air pollutants, and their precursors emitted by human activities. The TEM, developed by the U.S. Marine Biological Laboratory, is applied to document carbon and nitrogen flows among vegetation, soil, and atmosphere for terrestrial ecosystems of the globe. By linking these two models, we are able to downscale the land-use effects from the regional scale to the 0.5 degree longitude by 0.5 degree latitude grid-cell scale.
Policy Scenarios
The results of MIT models for the analysis of global primary energy demand are described and shown in the context of two scenarios identified as: (1) the no-policy scenario; and (2) the GHG mitigation policy scenario. The differences between the two scenarios are shown in Figs. 1(a, b) respectively.Fig. 1. Global primary energy demand, show in units of Exajoule (EJ) per year: (a) No policy to mitigate GHG (GHG) emissions; (b) GHG (GHG) mitigation policy [Source: EPPA simulation, August 2007]
In the no-policy scenario [Fig. 1(a)], we assume that there are no policies planned or in place to mitigate GHG emissions. In this scenario, according to the projections of the EPPA model, the cumulative GHG emissions in the United States would be 114 billion metric tons (bmt) of carbon equivalent for the period of 2012–2050, and of carbon equivalent for the period of 2051–2100, while the corresponding global levels would be 672 and , respectively.
In the GHG mitigation policy scenario [Fig. 1(b)] however, we assume that there are policies to limit GHG emissions. It specifies GHG mitigation to be achieved through 2050 for the standard six-gas basket of GHGs, including carbon dioxide , nitrous oxide , methane , hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride .
We apply the case-specifying reductions of GHG emissions in the United States of 50 percent below 1990 levels by 2050, and the other countries pursue GHG mitigation policies as follows: Europe, Japan, Canada, Australia, and New Zealand follow an allowance path that is falling gradually from the simulated Kyoto emissions levels in 2012 to 50 percent below 1990 in 2050. All other countries, mainly developing ones, adopt a policy beginning in 2025 and continuing through 2034 that holds emissions to the level in year 2015, and then maintains 2000 emission levels from 2035 to 2050. Such policies are extended through 2100 by holding annual emission allowances around their 2050 level through the end of the century.
Following the implementation of these GHG mitigation policies and based on the projection of the EPPA model, the cumulative number of GHG emissions in the United States would be of carbon equivalent for the period of 2012–2050 and of carbon equivalent for the period of 2051–2100, while the corresponding global levels would be 408 and , respectively.
If GHG mitigation policies were implemented, the world would need less energy considering that the mandatory mitigation on GHGs would limit the use of conventional energy sources such as coal and oil; however, we would need significant energy to be produced from biomass. The increasing demand for biomass energy would boost the value of land producing biomass energy, and this would increase the land-use conversion from agricultural uses to biomass.
Land-Use Conversion Analyses
The results of analyses indicate that biomass energy production would occur mainly in the United States, Central and South America, Africa, and Indonesia. The regional disparity in land use is affected by two factors: (1) in some regions like the United States, there is abundant available agricultural land, therefore leading to the occurrence of biomass production on a large scale considering that biomass would typically occur in agricultural land; and (2) biomass is more productive in tropical areas.
However, some regions with abundant agricultural land and in tropical areas, such as China and India, devote very little land to biomass energy production. An important reason is that in these regions, the demand for food would be very high considering their population; as a result, these regions would specialize in the production of crop products and livestock. In addition, international trade further drives the specialization of different agricultural products as well as biomass energy in various regions.
The large-scale development of biomass energy production would be conducted at the expense of agricultural land. Because of the relatively high availability and low cost to be converted to other land, unmanaged forestry land would decrease. As indicated in a comparison from the beginning to the end of the twenty-first century, in the policy case where there is an increased need for more land to be devoted to biomass energy production, unmanaged forestry land would experience a more severe loss than in the no-policy scenario.
Carbon Storage and Land Use
It has been commonly acknowledged that natural forest is a great reservoir for carbon storage. If we clear-cut significant areas of natural forest to provide cropland for biomass, would the carbon stored in agricultural land be reduced? The TEM was used to simulate the carbon stored in the five types of agricultural land as well as biomass land in both the no-policy and GHG mitigation policy scenarios, and the results are shown in Table 1.
Table 1. Carbon Stored in the Combined Five Types of Agricultural Land and Biomass Land
In the no-policy scenario, the carbon stored in the five types of agricultural land and biomass land would experience a loss from decade to decade as shown, with a total difference of during the twenty-first century, which is the difference between the values shown for 2100 and 2000. For the scenario of implementation of the GHG mitigation policies, there would be a greater decrease in stored carbon from decade to decade that would lead to carbon storage loss of .
According to the EPPA prediction, the reduction in GHG emissions in the policy scenario by using more biomass energy would be (carbon equivalent). However, in light of the results of Table 1, land-use conversion as a result of larger-scale production of biomass energy would increase the atmospheric GHG emissions by (carbon equivalent) during the twenty-first century. In other words, although the GHG mitigation policies would generally reduce the atmospheric GHG emissions by using more energy from biomass, part of the endeavors would be counteracted by the land-use conversion as a result of large-scale production of biomass energy.
Policy Decisions for the Future
In matters as complex as the Earth’s ecosystem and climate, policy decisions of any nature can have many consequences. This research indicates how policy makers should take the land-use effects of biomass energy production into consideration when developing GHG mitigation policies because the global capacity of agricultural land to store carbon might be diminished, and thereby reduce the overall effectiveness of GHG mitigation endeavors. The analyses indicate that the use of biomass fuels—like all technologies—should be viewed as solutions with tradeoffs and implications for other components of mitigation strategies.
This view should in turn be reflected in other policy matters and decisions regarding which technologies to focus on and how economic resources would be devoted to the various other strategies to mitigate global warming. On matters so crucial for humanity’s future, we must do our utmost to discern all the implications of proposed GHG mitigation policies and the degrees to which they are likely to enhance our future.
Xiaodong Wang is a consultant with PB Strategic Consulting. He can be reached at [email protected].
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