JP

Contribution of anaerobic digesters to emissions mitigation under US climate policy

Livestock husbandry in the U.S. significantly contributes to many environmental problems, including the release of methane, a potent greenhouse gas (GHG). Anaerobic digesters (ADs) break down organic wastes using bacteria that produce methane, which can be collected and combusted to generate electricity. ADs also reduce odors and pathogens that are common with manure storage and the digested manure can be used as a fertilizer. There are relatively few ADs in the U.S., mainly due to their high capital costs. We use the MIT Emissions Prediction and Policy Analysis (EPPA) model to test the effects of a representative U.S. climate stabilization policy on the adoption of ADs which sell electricity and generate methane mitigation credits. Under such policy, ADs become competitive at producing electricity in 2025, when they receive methane reduction credits and electricity from fossil fuels becomes more expensive. We find that ADs have the potential to generate 5.5% of U.S. electricity.

Costs of Mitigating Climate Change in the United States

We consider the large range of estimated costs of meeting U.S. climate policy targets. Some of this range is due to different studies using different cost measures, and in principle such differences could be eliminated by more careful comparisons and greater transparency in studies that estimate costs. Still another source of differences is how the proposed policy is represented. Here, again, this source of difference could be reduced by more careful comparison and by better definition of implementation details. Even if these sources of difference could be eliminated, there would remain substantial uncertainties because of the difficulties of projecting economic activity over the long horizon of proposed policies.We show the importance of several of these factors, using a consistent modeling framework.

Crop Response to Elevated CO2 and World Food Supply: A Comment on "Food for Thought..." by Long et al., Science 312:1918-1921, 2006

Recent conclusions that new free-air carbon dioxide enrichment (FACE) data show a much lower crop yield response to elevated CO2 than thought previously—casting serious doubts on estimates of world food supply in the 21st century—are found to be incorrect, being based in part on technical inconsistencies and lacking statistical significance. First, we show that the magnitude of crop response to elevated CO2 is rather similar across FACE and non-FACE data-sets, as already indicated by several previous comprehensive experimental and modeling analyses, with some differences related to which "ambient" CO2 concentration is used for comparisons. Second, we find that results from most crop model simulations are consistent with the values from FACE experiments. Third, we argue that lower crop responses to elevated CO2 of the magnitudes in question would not significantly alter projections of world food supply. We conclude by highlighting the importance of a better understanding of crop response to elevated CO2 under a variety of experimental and modeling settings, and suggest steps necessary to avoid confusion in future meta-analyses and comparisons of experimental and model data.

Cross-Border Trading and Borrowing in the EU ETS

This paper exploits a little used data resource within the central registry of the European Unions Emissions Trading System (EU ETS) to analyze cross border trading and inter-year borrowing during the first trading period (2005- 2007). Cross-border flows were small in the aggregate but remarkably frequent in matching allowance deficits and surpluses at the installation level throughout the EU. These data also indicate that a novel feature of the EU ETSthe ability to borrow allowances from the forward allocation to satisfy current compliance requirementswas also used. These data provide evidence that the precondition of efficient abatement in a cap-and-trade systemwidespread use of trading opportunitieswas present in the first period of the EU ETS.

Dependence of the ocean-atmosphere partitioning of carbon on temperature and alkalinity

We develop and extend a theoretical framework to analyze the impacts of changes in temperature and alkalinity on the ocean-atmosphere carbon partitioning. When investigating the impact of temperature, we assume that there is no change in the global ocean alkalinity. This idealized situation is probably most relevant on intermediate timescales of hundreds to thousands of years. Our results show that atmospheric pCO2 depends approximately exponentially on the average ocean temperature, since the chemical equilibria involved have an exponential (Arrhenius-type) dependence. The dependence of pCO2 on alkalinity is more complicated, and our theory suggests several regimes. The current ocean-atmosphere system appears to have an exponential dependence of pCO2 on global mean ocean alkalinity, but at slightly higher alkalinities, the dependence becomes a power law. We perform experiments with a numerical physical-biogeochemical model to test the validity of our analytical theory in a more complex, ocean-like system: in general, the numerical results support the analytical inferences.< br />
©2011 American Geophysical Union.

Deriving emissions times series from sparse atmospheric mole fractions

A growth-based Bayesian inverse method is presented for deriving emissions of atmospheric trace species from temporally sparse measurements of their mole fractions. This work is motivated by many recent studies that have deduced emissions using archived air samples with measurement intervals of the order of a year or longer in the early part of the record. Several techniques have been used to make this underdetermined problem invertible. These include the incorporation of prior emissions estimates, the smoothing of observations or derived emissions, the approximation of emissions time series by polynomials, or the application of regularization schemes. However, these methods often suffer from limitations, such as the unavailability of independent, unbiased priors, the emergence of unrealistic emissions fluctuations due to measurement outliers, or the subjective choice of measurement or emissions smoothing time scales. This paper presents an alternative solution that reduces the influence of potentially biased priors or measurement outliers by constraining the emissions growth rate around some growth estimate, in conjunction with the model-measurement mismatch.

Description and Validation of the MIT Version of the GISS 2-D Model

A significant number of long-term climate change simulations are to be carried out in the Integrated Framework of the MIT Global Change Joint Program. Since Global Circulation Models (GCMs) require an enormous amount of computer time, the two-dimensional statistical-dynamic model developed by Stone and Yao was chosen to be used for the initial stage of the Joint Program. At MIT, the model has been modified to make it more suitable for the purposes of the Joint Program, including developing a new scheme for a surface flux calculation. A number of simulations with the modified version of the model have been performed in which a few schemes for cloud and ocean heat transport calculation have been tested. Comparisons of the results of the present climate simulations with observational data show that the model reasonably reproduces main features of zonally averaged atmospheric circulation. A climate sensitivity produced by the model coupled with a mixed layer ocean model in response to the doubling of the atmospheric CO2 concentration lies in the range of the results obtained with GCMs. The results of the simulations with a gradual increase of the greenhouse gas concentrations in the atmosphere, in which diffusion of heat into the deep ocean was taken into account, are also similar to those obtained in the analogous simulations with GCMs. As a whole, presented results demonstrate that the modified version of the two-dimensional model can be successfully used for climate change predictions in the Integrated Framework of the Joint Program.

Designing a US Market for CO2

In this paper we focus on one component of the cap-and-trade system: the markets that arise for trading allowances after they have been allocated or auctioned. The efficient functioning of the market is key to the success of cap-and-trade as a system. We review the performance of the EU CO2 market and the U.S. SO2 market and examine how the flexibility afforded by banking and borrowing, and the limitations on banking and borrowing, have impacted the evolution of price in both markets. While both markets have generally functioned well, certain episodes illustrate the importance of designing the rules to encourage liquidity in the market.

Designing a U.S. Market for CO2

The United States may soon have a market for carbon. If so, that market will grow out of a cap-and-trade system like the EU's Emissions Trading System for CO2 or the U.S. Acid Rain Program for SO2. This article reviews the historical performance of these two markets, with particular focus on how the flexibility afforded by, as well as restrictions on, the "banking" and borrowing of allowances has affected the evolution of prices. While both markets have generally functioned well, four episodes are used to illustrate the importance of designing the rules to encourage such flexibility. The 2005 opening of the EU CO2 market was marked by a surprisingly high price, one that resulted from a delay in institutions with long positions in allowances ("longs") bringing supply to the market. The 2007 close of the first phase produced a sharp divergence between the spot price at the end of 2007 and the futures price for 2008, reflecting the restriction against carrying over (or "banking") allowances from one phase to the next. The U.S. SO2 market's transition to a tighter system in 2000 avoided such a divergence by allowing unlimited banking of allowances into the second phase. In 2005-2006, the U.S. SO2 market experienced a surprising price spike attributable to a combination of changing fundamentals and institutional features (notably, the tax treatment of "longs") that undermined the flexibility of the bank.

Designing tradable permits system to control SO2 emissions in China: Principles and practices

This paper discusses the problems of implementing a cap-and-trade system for controlling [SO.sub.2] emissions in China. It describes the evolution of current air emissions policy for [SO.sub.2] emissions and focuses on two critical aspects for establishing a tradable permits system in China: the transition from (nontradable) facility-specific permits to tradable (emission) permits and the integration of tradable permits with the pre-existing pollution levy system. A major theme throughout the paper is that the requirements for establishing an effective tradable permits system do not differ greatly from those for an equally effective tax or command-and-control regime. Although each instrument has distinctive features, the differences among them are mainly ones of form. All require that the same fundamental problems be solved: How to allocate the cost burden of reducing emissions, what specific requirements to place on emitting sources, and how to ensure compliance.

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