JP

Impacts on Resources and Climate of Projected Economic and Population Growth Patterns

Global economic and population growth are driving energy, land, and water use, and there are complex connections between the use of these resources and the world’s climate and natural environment. A significant engineering challenge is to develop and deploy technologies that reduce human impact on the environment and make better use of resources while remaining robust in the face of unavoidable environmental change. Without significant changes in resource use patterns, projections indicate that fossil fuel use will continue to rise, more land will be converted for crops, and water stress will increase in many areas already subject to water shortages.

Even in the absence of climate and environmental change, these trends would lead to stress on water resources and natural systems as well as temperature increases of 3°C to as much as 8°C depending on the region and climate sensitivity. Higher global temperatures would be associated with an overall increase in global precipitation (because a warmer climate speeds up the hydrological cycle, meaning more evaporation and more precipitation), but water runoff in many already water-stressed areas could be reduced, contributing to further water stress, with consequences for energy and food production.

This short paper presents a review of several key aspects of current global development to quantitatively describe how economic development drives energy, land, and water use and how the use of these resources may affect climate and the availability of resources.

Increase in HFC-134a emissions in response to the success of the Montreal Protocol

The 1,1,1,2-tetrafluoroethane (HFC-134a), an important alternative to CFC-12 in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer, is a high global warming potential greenhouse gas. Here we evaluate variations in global and regional HFC-134a emissions and emission trends, from 1995 to 2010, at a relatively high spatial and temporal (3.75° in longitude × 2.5° in latitude and 8 day) resolution, using surface HFC-134a measurements. Our results show a progressive increase of global HFC-134a emissions from 19 ± 2 Gg/yr in 1995 to 167 ± 5 Gg/yr in 2010, with both a slowdown in developed countries and a 20%/yr increase in China since 2005. A seasonal cycle is also seen since 2002, which becomes enhanced over time, with larger values during the boreal summer.

Is Current Irrigation Sustainable in the United States? An Integrated Assessment of Climate Change Impact on Water Resources and Irrigated Crop Yields

While the impact of climate change on crop yields has been extensively studied, the quantification of water shortages on irrigated crop yields has been regarded as more challenging due to the complexity of the water resources management system. To investigate this issue, we integrate a crop yield reduction module and a water resources model into the MIT Integrated Global System Modeling (IGSM) framework, an integrated assessment model that links a model of the global economy to an Earth system model. While accounting for uncertainty in climate change, we assess the effects of climate and socio-economic changes on the competition for water resources between industrial, energy, domestic and irrigation; the implications for water availability for irrigation; and the subsequent impacts on crop yields in the US by 2050. We find that climate and socio-economic changes will increase water shortages and strongly reduce irrigated crop yields in specific regions (mostly in the Southwest), or for specific crops (i.e. cotton and forage). While the most affected regions are usually not major crop growers, the heterogeneous response of crop yield to global change and water stress suggests that some level of adaptation can be expected, such as the relocation of cropland area to regions where irrigation is more sustainable. Finally, GHG mitigation has the potential to alleviate the effect of water stress on irrigated crop yields—enough to offset the reduced CO2 fertilization effect compared to an unconstrained GHG emission scenario.

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

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.

Launching a New Climate Regime

At the 2015 UN Framework Convention on Climate Change (UNFCCC) meeting in Paris, participants in a new international climate agreement will volunteer Nationally Determined Contributions to emissions reductions. To put the planet on a path to declared temperature goals, the growth of global greenhouse gas emissions must cease, and begin to decline, by 2035 to 2040; however, the expected contributions do not yield results consistent with this timeline. Three achievements in Paris and follow-on activities are then crucial components of the new climate regime: a robust system of review with widely accepted measures of national effort; an established, durable plan of future pledge cycles; and increased financial support for the mitigation efforts of less developed countries. The MIT Economic Projection and Policy Analysis (EPPA) model is applied to assess emissions outcomes of expected pledges and national performances in meeting them, and to elaborate the components of a successful launch.

Limited trading of emissions permits as a climate cooperation mechanism? US–China and EU–China examples

Recent multilateral climate negotiations have underlined the importance of international cooperation and the need for support from developed to developing countries to address climate change. This raises the question of whether carbon market linkages could be used as a cooperation mechanism. Policy discussions surrounding such linkages have indicated that, should they operate, a limit would be set on the amount of carbon permits that could be imported by developed regions from developing countries. This paper analyzes the impact of limited carbon trading between an ETS in the EU or the US and a carbon market covering Chinese electricity and energy intensive sectors using a global economy-wide model. We find that the limit results in different carbon prices between China and Europe or the US. Although the impact on low-carbon technologies in China is moderate, global emission reductions are deeper than in the absence of international trading due to reduced carbon leakage. If China captures the rents associated with limited permit trading, we show that it is possible to find a limit threshold that makes both regions better off relative to carbon markets operating in isolation.

Long-term economic modeling for climate change assessment

A growing concern for using large scale applied general equilibrium models to analyze energy and environmental policies has been whether these models produce reliable projections. Based on the latest MIT Economic Projection and Policy Analysis model we developed, this study aims to tackle this question in several ways, including enriching the representation of consumer preferences to generate changes in consumption pattern consistent to those observed in different stages of economic development, comparing results of historical simulations against actual data, and conducting sensitivity analyses of future projections to key parameters under various policy scenarios. We find that: 1) as the economies grow, the empirically observed income elasticities of demand are better represented by our setting than by a pure Stone–Geary approach, 2) historical simulations in general perform better in developed regions than in developing regions, and 3) simulation results are more sensitive to GDP growth than energy and non-energy substitution elasticities and autonomous energy efficiency improvement.

Metamodeling of Droplet Activation for Global Climate Models

The nucleation of cloud droplets from the ambient aerosol is a critical physical process that must be resolved for global models to faithfully predict aerosol–cloud interactions and aerosol indirect effects on climate. To better represent droplet nucleation from a complex, multimodal, and multicomponent aerosol population within the context of a global model, a new metamodeling framework is applied to derive an efficient and accurate activation parameterization. The framework applies polynomial chaos expansion to a detailed parcel model in order to derive an emulator that maps thermodynamic and aerosol parameters to the supersaturation maximum achieved in an adiabatically ascending parcel and can be used to diagnose droplet number from a single lognormal aerosol mode. The emulator requires much less computational time to build, store, and evaluate than a high-dimensional lookup table. Compared to large sample sets from the detailed parcel model, the relative error in the predicted supersaturation maximum and activated droplet number computed with the best emulator is -0.6% ± 9.9% and 0.8% ± 17.8% (one standard deviation), respectively. On average, the emulators constructed here are as accurate and between 10 and 17 times faster than a leading physically based activation parameterization. Because the underlying parcel model being emulated resolves size-dependent droplet growth factors, the emulator captures kinetic limitations on activation. The results discussed in this work suggest that this metamodeling framework can be extended to accurately account for the detailed activation of a complex aerosol population in an arbitrary coupled global aerosol–climate model.

Modeling intermittent renewable electricity technologies in general equilibrium models

Economy-wide top-down (TD) equilibrium models have traditionally proved to be valuable tools for assessing energy and climate policies. New modeling challenges brought about by intermittent renewable energy sources, however, require a careful review of existing tools. This paper presents an overview of TD modeling approaches for incorporating renewable energy and describes in detail one approach, using the MIT USREP model, to identify critical parameters and assumptions underlying the general equilibrium formulation. We then quantitatively assess its performance regarding the ability to correctly estimate the participation of intermittent renewables in the electricity sector as predicted by a bottom-up electricity sector model, which is designed to analyze the expansion and operation of a system with a large penetration of wind and which is integrated within an economy-wide general equilibrium framework. We find that a properly specified TD approach to modeling intermittent renewable energy is capable of roughly replicating the results from the benchmark model. We argue, however, that the general equilibrium approach is highly sensitive to key parameters which are a priori typically unknown or at least highly uncertain. Our analysis suggests that traditional TD simulation tools have to be enhanced to avoid potentially misrepresenting the implications of future climate policies where presumably renewable energy could participate at large scale. Detailed power system models that capture system reliability and adequacy constraints are needed to properly assess the potential of renewable energy.

Modeling Regional Transportation Demand in China and the Impacts of a National Carbon Policy

China's climate and energy policy commitments are stated at the national level, but they may have uneven impacts on the country's regionally heterogeneous transport system. This work quantifies the expected provincial-level response of freight transport to an economywide policy targeting reductions in carbon emissions intensity. The analysis applies the China Regional Energy Model, a multisector, static, global, computable general equilibrium (CGE) model representing 30 individual provinces with physical accounts of energy and greenhouse gas emissions. The structure of road and nonroad freight (and passenger) sectors, the preparation of transport activity data, and a policy similar to announced goals that specify a 17% reduction in the carbon dioxide emissions intensity of gross domestic product are described. In the national aggregate and in most provinces, the road freight sector is most affected by the emissions intensity cap. The road freight sector contributes 24%—versus 18% from nonroad freight and 51% from nontransport sectors—of a 5.1% reduction in national refined oil demand. Significant regional differences are found in the impacts of a national-level, economywide policy. Steep reductions in freight activity occur in some of the poorest provinces, partly because they offer low-cost abatement opportunities, and the resulting adjustments across the economy affect transport demand. This research contributes a new tool capable of capturing the transport impact of sector- and province-specific policies in detail and providing a rigorous foundation for future dynamic CGE analyses. Potential impacts of energy and climate policy on regional transport systems are important inputs to policy and infrastructure investment decisions at the central and local levels.

MIT Global Change

JP

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