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Examination of Climate Response to Historical and Projected Forcings over Years 850-4000 with the MIT IGSM

The MIT IGSM is used for a study of the climate response to various historical and projected forcings over the period 850-4000 AD. The MIT IGSM includes a zonally-averaged atmospheric model coupled to land and ocean models. Both land and ocean models simulate carbon cycle. Two configurations of the IGSM were used in the simulations; one with the MIT 3D OGCM and other with anomaly diffusing ocean model. Over the period 850-2005, a historical run with all time-varying natural and anthropogenic forcings is compared to a set of runs where only a single component of the forcing time series is varied. Over 2005-3000, climate projections as forced by four different Representation Concentration Pathways are compared. These projections are extended by decreasing forcings back to pre-industrial levels over years 3000-4000. In addition to changes in surface air temperature, carbon uptake in the ocean and land systems and changes in the oceans’ large-scale circulation are a focus in analyses of these simulations. Simulations with interactive carbon cycle and prescribed carbon emissions were also carried out. Dependency of the projected changes on assumptions about climate system parameters, such as climate sensitivity, rate of oceanic heat uptake and aerosol forcing were studied using the IGSM with simplified ocean model.

Expanding International GHG Emissions Trading: The Role of Chinese and U.S. Participation

The marked-based emission trading system is regarded as a cost effective way to facilitate emission abatement and is expected to play an essential role in international cooperation for global climate mitigation. The European Union Emissions Trading System (EU-ETS) has been fully operation since 2007. In 2012, Australia announced its intention to link to the EU-ETS starting in 2015. This research considers the implications of expanding these linkages further to include China and (or) the United States. We simulate an extended international emission market, beginning by analysing the implications of the EU-Australia/New Zealand (NZ) linkage (assuming New Zealand links to the Australian market) based on currently announced policy targets. We then extend the system to include China, and compare it to an Australia/NZ-EU-US linkage in terms of the impact on greenhouse gas (GHG) emissions at the global, national and sectoral level, the carbon-equivalent price by region (or for the ETS linked regions), and primary energy use at the global sectoral level, with attention to quantifying any leakage effects.

We employ the China-in-Global Energy Model (CGEM) for this analysis. The CGEM is a multi-regional, multi-sector, recursive-dynamic computable general equilibrium (CGE) model of the global economy that separately represents 19 regions and 18 sectors. For this work, we use the Global Trade Analysis Project 2007 data set (GTAP 8), which was released in the spring of 2012. To analyse the individual and combined impact of including China and US in an integrated global emissions trading market, we develop several scenarios, including a No-ETS scenario to serve as a baseline “No Policy” scenario, and a “reference” scenario that imposes emissions trading in each region without linkages. These scenarios include: EU-Australia/NZ, EU-Australia/NZ-China, EU-Australia/NZ-US, and EU-Australia-China-US. Other scenarios involve simulating the these cap-and-trade policies...

Expectations for a New Climate Agreement

With the objective of stimulating timely and open discussion of the current attempt to formulate a new climate agreement—to be reached at the 21st meeting of the Conference of Parties (COP-21) in Paris during November of 2015—analysis is conducted of the expected developments in the lead-up negotiations. Based on the assumption that the architecture of the agreement will likely involve voluntary pledges and ex-post review (akin to the Copenhagen Accord), the domestic policies and measures expected to underlie national negotiating positions are described. Applying a global economic model, the effect of these Nationally Determined Contributions (NDCs) on global greenhouse gas emissions is assessed. The analysis shows that an agreement likely achievable at COP-21 will succeed in a useful bending the curve of global emissions. The likely agreement will not, however, produce global emissions within the window of paths to 2050 that are consistent with frequently proposed climate goals, raising questions about follow-up steps in the development of a climate regime.

Exploring the Terrestrial Ecosystem Response to Extreme Weather Events using Multiple Land Surface Model

This study investigates the complex terrestrial ecosystems response to extreme weather events using three different land surface models. Previous studies have showed that extreme weather events can have serious and damaging impacts on human and natural systems and they are most evident on regional and local scales. Under climate change, extreme weather events are likely to increase in both magnitude and frequency, making realistic simulation of ecosystems response to extreme events more essential than ever in assessing the potential damaging impacts. Three different land surface models are used to explore the impacts of extreme events on regional to continental ecosystem responses. The Terrestrial Ecosystem Model (TEM) is a process-based ecosystem model that uses spatially referenced information on climate, elevation, soils, vegetation and water availability to make monthly estimates of vegetation and soil carbon and nitrogen fluxes and pool sizes. The Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) is a multi-layered land surface model based on eddy-covariance theory to calculate the biosphere-atmosphere exchanges of carbon dioxide, water, and momentums. The Community Land Model (CLM) is a community-based model widely used in global-scale land data assimilation research. The study focuses on the complex interactions and feedbacks between the terrestrial ecosystem and the atmosphere such as water cycle, carbon and nitrogen budgets, and environmental conditions. The model simulations and performances are evaluated using the biogeophysical and micrometeorological observation data from the AmeriFlux sites across the continental US. This study compares and evaluates the ability of different models and their key components to capture terrestrial response to extreme weather events.

Factors controlling diazotroph biogeography

We present a theoretical framework, which considers the competition for iron, phosphorus and nitrogen resources to explain the biogeography of nitrogen fixing autotrophs (diazotrophs). Here we assume that diazotrophs require higher iron quotas, and have slower maximum growth relative to other phytoplankton. The theory then suggests that the rate of supply of iron or phosphorus relative to the supply of fixed nitrogen sets the regions where diazotroph can coexist with other phytoplankton. The framework also indicates that iron, phosphate and fixed nitrogen concentrations can be strongly controlled by the local phytoplankton community. We show that the framework allows us to divide the ocean of an earth system model into five clearly defined biogeographical provinces. We consider how these province boundaries shift in a warming world based on the changes to the relative supplies of fixed nitrogen, iron and phosphate.

Field Measurement of the Fate of Atmospheric H2 in a Forest Environment: from Canopy to Soil

Atmospheric hydrogen (H2), an indirect greenhouse gas, plays a notable role in the chemistry of the atmosphere and ozone layer. Current anthropogenic emissions of H2 are substantial and may increase with its widespread use as a fuel. The H2 budget is dominated by the microbe-mediated soil sink, and although its significance has long been recognized, our understanding is limited by the low temporal and spatial resolution of traditional field measurements. This thesis was designed to improve the process-based understanding of the H2 soil sink with targeted field and lab measurements.

In the field, ecosystem-scale flux measurements of atmospheric H2 were made both above and below the forest canopy for over a year using a custom, automated instrument at the Harvard Forest. H2 fluxes were derived using a flux-gradient technique from the H2 concentration gradient and the turbulent eddy coecient. A ten-fold improvement in precision was attained over traditional systems, which was critical for quantifying the 2 concentration gradients above the turbulent forest canopy. Soil uptake of atmospheric H2 was the dominant process in this forest ecosystem. Rates peaked in the summer and persisted at reduced levels in the winter season, even across a 70 cm snowpack. We present correlations of the H2 flux with environmental variables (e.g., soil temperature and moisture). This work is the most comprehensive attempt to elucidate the processes controlling biosphere-atmosphere exchange of H2. Our results will help reduce uncertainty in the present-day H2 budget and improve projections of the response of the H2 soil sink to global change.

In the lab, we isolated microbial strains of the genus Streptomyces from Harvard Forest and found that the genetic potential for atmospheric H2 uptake predicted H2 consumption activity. Furthermore, two soil Actinobacteria were found to utilize H2 only during specic lifecycle stages. The lifecycle of soil microorganisms can be quite complex as an adaptation to variable environmental conditions. Our results indicate that H2 may be an important energetic supplement to soil microorganisms under stress. These results add to the understanding of the connections between the environment, organismal life cycle, and soil H2 uptake.

Firm-level determinants of energy and carbon intensity in China

In recent years, China׳s leaders have sought to coordinate official energy intensity reduction targets with new targets for carbon dioxide (CO2) intensity reduction. The Eleventh Five-Year Plan (2006–2010) included for the first time a binding target for energy intensity, while a binding target for CO2 intensity was included later in the Twelfth Five-Year Plan (2011–2015). Using panel data for a sample of industrial firms in China covering 2005 to 2009, we investigate the drivers of energy intensity reduction (measured in terms of direct primary energy use and electricity use) and associated CO2 intensity reduction. Rising electricity prices were associated with decreases in electricity intensity and increases in primary energy intensity, consistent with a substitution effect. Overall, we find that energy intensity reduction by industrial firms during the Eleventh Five-Year Plan translated into more than proportional CO2 intensity reduction because reducing coal use—in direct industrial use as well as in the power sector—was a dominant abatement strategy. If similar dynamics characterize the Twelfth Five-Year Plan (2011–2015), the national 17 percent CO2 intensity reduction target may not be difficult to meet—and the 16 percent energy intensity reduction target may result in significantly greater CO2 intensity reduction.

© 2015 Elsevier Ltd

Fiscal consolidation and climate policy: An overlapping generations perspective

This paper examines the distributional and efficiency impacts of public debt consolidation financed through a carbon tax employing a dynamic general-equilibrium model with overlapping generations of the U.S. economy. The numerical model features government taxes and spending and a multi-sectoral production structure including intermediate production, specific detail on the energy sector both in terms of primary energy carriers and energy-intensive industries, and sector- and fuel-specific carbon inputs. In contrast to revenue-neutral carbon tax swaps, using the carbon revenue for deficit reduction implies a relaxation of future public budgets as debt repayment results in lower future interest obligations.While intergenerational welfare impacts depend importantly on what tax recycling instrument is used, we find that combining public debt consolidation with a carbon policy entails the possibility of sustained welfare gains for future generations. If social discount rates are sufficiently low or if social preferences exhibit a large aversion with respect to intergenerational inequality, combining fiscal consolidation and climate policy may offer the chance for societal gains even without considering potential benefits from averted climate change.

© 2013 Elsevier B.V.

Flexible NOx Abatement from Power Plants in the Eastern United States

Emission controls that provide incentives for maximizing reductions in emissions of ozone precursors on days when ozone concentrations are highest have the potential to be cost-effective ozone management strategies. Conventional prescriptive emissions controls or cap-and-trade programs consider all emissions similarly regardless of when they occur, despite the fact that contributions to ozone formation may vary. In contrast, a time-differentiated approach targets emissions reductions on forecasted high ozone days without imposition of additional costs on lower ozone days. This work examines simulations of such dynamic air quality management strategies for NOx emissions from electric generating units. Results from a model of day-specific NOx pricing applied to the Pennsylvania–New Jersey–Maryland (PJM) portion of the northeastern U.S. electrical grid demonstrate (i) that sufficient flexibility in electricity generation is available to allow power production to be switched from high to low NOx emitting facilities, (ii) that the emission price required to induce EGUs to change their strategies for power generation are competitive with other control costs, (iii) that dispatching strategies, which can change the spatial and temporal distribution of emissions, lead to ozone concentration reductions comparable to other control technologies, and (iv) that air quality forecasting is sufficiently accurate to allow EGUs to adapt their power generation strategies.

© 2012 American Chemical Society

Food benefit and climate warming potential of nitrogen fertilizer uses in China

Chemical nitrogen (N) fertilizer has long been used to help meet the increasing food demands in China, the top N fertilizer consumer in the world. Growing concerns have been raised on the impacts of N fertilizer uses on food security and climate change, which is lack of quantification. Here we use a carbon–nitrogen (C–N) coupled ecosystem model, to quantify the food benefit and climate consequence of agronomic N addition in China over the six decades from 1949 to 2008. Results show that N fertilizer-induced crop yield and soil C sequestration had reached their peaks, while nitrous oxide (N2O) emission continued rising as N was added. Since the early 2000s, stimulation of excessive N fertilizer uses to global climate warming through N2O emission was estimated to outweigh their climate benefit in increasing CO2 uptake. The net warming effect of N fertilizer uses, mainly centered in the North China Plain and the middle and lower reaches of Yangtze River Basin, with N2O emission completely counteracting or even exceeding, by more than a factor of 2, the CO2 sink. If we reduced the current N fertilizer level by 60% in 'over-fertilized' areas, N2O emission would substantially decrease without significantly influencing crop yield and soil C sequestration.

© 2012 IOP Publishing Ltd

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