JP

Valuing Climate Impacts in Integrated Assessment Models: The MIT IGSM

We discuss a strategy for investigating the impacts of climate change on Earth’s physical, biological and human resources and links to their socio-economic consequences. The features of the integrated global system framework that allows a comprehensive evaluation of climate change impacts are described with particular examples of effects on agriculture and human health. We argue that progress requires a careful understanding of the chain of physical changes—global and regional temperature, precipitation, ocean acidification and polar ice melting. We relate those changes to other physical and biological variables that help people understand risks to factors relevant to their daily lives—crop yield, food prices, premature death, flooding or drought events, land use change. Finally, we investigate how societies may adapt, or not, to these changes and how the combination of measures to adapt or to live with losses will affect the economy. Valuation and assessment of market impacts can play an important role, but we must recognize the limits of efforts to value impacts where deep uncertainty does not allow a description of the causal chain of effects that can be described, much less assigned a likelihood. A mixed approach of valuing impacts, evaluating physical and biological effects, and working to better describe uncertainties in the earth system can contribute to the social dialogue needed to achieve consensus—where it is needed—on the level and type of mitigation and adaptation actions that are required.

Volcanic contribution to decadal changes in tropospheric temperature

Despite continued growth in atmospheric levels of greenhouse gases, global mean surface and tropospheric temperatures have shown slower warming since 1998 than previously. Possible explanations for the slow-down include internal climate variability, external cooling influences and observational errors. Several recent modelling studies have examined the contribution of early twenty-first-century volcanic eruptions to the muted surface warming. Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect. To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.

Water consumption footprint and land requirements of large-scale alternative diesel and jet fuel production

Middle distillate (MD) transportation fuels, including diesel and jet fuel, make up almost 30% of liquid fuel consumption in the United States. Alternative drop-in MD and biodiesel could potentially reduce dependence on crude oil and the greenhouse gas intensity of transportation. However, the water and land resource requirements of these novel fuel production technologies must be better understood. This analysis quantifies the lifecycle green and blue water consumption footprints of producing: MD from conventional crude oil; Fischer–Tropsch MD from natural gas and coal; fermentation and advanced fermentation MD from biomass; and hydroprocessed esters and fatty acids MD and biodiesel from oilseed crops, throughout the contiguous United States. We find that FT MD and alternative MD derived from rainfed biomass have lifecycle blue water consumption footprints of 1.6 to 20.1 L_water/L_MD, comparable to conventional MD, which ranges between 4.1 and 7.4 L_water/L_MD. Alternative MD derived from irrigated biomass has a lifecycle blue water consumption footprint potentially several orders of magnitude larger, between 2.7 and 22 600 L_water/L_MD. Alternative MD derived from biomass has a lifecycle green water consumption footprint between 1.1 and 19 200 L_water/L_MD. Results are disaggregated to characterize the relationship between geo-spatial location and lifecycle water consumption footprint. We also quantify the trade-offs between blue water consumption footprint and areal MD productivity, which ranges from 490 to 4200 L_MD/ha, under assumptions of rainfed and irrigated biomass cultivation. Finally, we show that if biomass cultivation for alternative MD is irrigated, the ratio of the increase in areal MD productivity to the increase in blue water consumption footprint is a function of geo-spatial location and feedstock-to-fuel production pathway.

Water-CO2 Tradeoffs in Electricity Generation Planning

In 2011, the state of Texas experienced the lowest annual rainfall on record, with similar droughts affecting East Africa, China and Australia. Climate change is expected to further increase the likelihood and severity of future droughts. Simultaneously, population and industrial growth increases demand for drought-stressed water resources and energy, including electricity. In the US, nearly half of water withdrawals are for electricity generation, much of which comes from greenhouse gas emitting fossil fuel combustion. The result is a three-way tension among efforts to meet growing energy demands while reducing greenhouse gas emissions and water withdrawals, a critical issue within the so-called water–energy nexus. We focus on this interaction within the electric sector by using a generation expansion planning model to explore the trade-offs. We show that large reductions in CO₂ emissions would probably increase water withdrawals for electricity generation in the absence of limits on water usage, and that simultaneous restriction of CO₂ emissions and water withdrawals requires a different mix of energy technologies and higher costs than one would plan to reduce either CO₂ or water alone.

What GHG Concentration Targets are Reachable in this Century?

We offer simulations that help to understand the relationship between GHG emissions and concentrations, and the relative role of long-lived (e.g., CO2) and short-lived (e.g., CH4) emissions. We show that, absent technologies to remove CO2 from the atmosphere, the 350 CO2 ppm target is out of reach in this century, even if all emissions drop to zero almost immediately (i.e. in 2015). A 350 ppm CO2-equivalent target is potentially achievable, but would require CH4 concentrations falling below preindustrial levels, and thus elimination of emissions from human activities such as rice and livestock agriculture. More realistically, even some of the most aggressive targets proposed through 2035 would lead to concentrations (CO2 or CO2-eq) in the 415–450 ppm range. This is only feasible if after 2035 emissions continued a downward path toward zero. Only in these cases would the temperature target of no more than 2 °C above preindustrial be achieved, and only after peaking above that level before declining.

Why do global long-term scenarios for agriculture differ? An overview of the AgMIP Global Economic Model Intercomparison

Recent studies assessing plausible futures for agricultural markets and global food security have had contradictory outcomes. To advance our understanding of the sources of the differences, 10 global economic models that produce long-term scenarios were asked to compare a reference scenario with alternate socioeconomic, climate change, and bioenergy scenarios using a common set of key drivers. Several key conclusions emerge from this exercise: First, for a comparison of scenario results to be meaningful, a careful analysis of the interpretation of the relevant model variables is essential. For instance, the use of “real world commodity prices” differs widely across models, and comparing the prices without accounting for their different meanings can lead to misleading results. Second, results suggest that, once some key assumptions are harmonized, the variability in general trends across models declines but remains important. For example, given the common assumptions of the reference scenario, models show average annual rates of changes of real global producer prices for agricultural products on average ranging between −0.4% and +0.7% between the 2005 base year and 2050. This compares to an average decline of real agricultural prices of 4% p.a. between the 1960s and the 2000s. Several other common trends are shown, for example, relating to key global growth areas for agricultural production and consumption. Third, differences in basic model parameters such as income and price elasticities, sometimes hidden in the way market behavior is modeled, result in significant differences in the details. Fourth, the analysis shows that agro-economic modelers aiming to inform the agricultural and development policy debate require better data and analysis on both economic behavior and biophysical drivers. More interdisciplinary modeling efforts are required to cross-fertilize analyses at different scales.

Will Economic Restructuring in China Reduce Trade-Embodied CO2 Emissions?

We calculate CO2 emissions embodied in China’s net exports using a multi-regional input-output database. We find that the majority of China’s export-embodied CO2 is associated with production of machinery and equipment rather than energy-intensive products, such as steel and aluminum. In 2007, the largest net recipients of embodied CO2 emissions from China include the EU (360 million metric tons, mmt), the U.S. (337 mmt), and Japan (109 mmt). Overall, annual CO2 emissions embodied in China’s net exports totaled 1,177 mmt, equal to 22% of China’s total CO2 emissions. We also develop a global general equilibrium model with a detailed treatment of energy and CO2 emissions. We use the model to analyze the impact of a sectoral shift in the Chinese economy away from industry and towards services, both without and with a decrease in China’s trade surplus, and a tax on energy-intensive exports, which reflect policy objectives in China’s Twelfth Five-Year Plan (2011–2015). We find that without a decrease in the trade surplus, both policies will have a limited impact on China’s net exports of embodied CO2 emissions. The policies have an even smaller effect on global emissions, as reduced production in China is partially offset by increased production elsewhere.

Winners and losers: Ecological and biogeochemical changes in a warming ocean

We employ a marine ecosystem model, with diverse and ï¬‚exible phytoplankton communities, coupled to an Earth system model of intermediate complexity to explore mechanisms that will alter the biogeography and productivity of phytoplankton populations in a warming world. Simple theoretical frameworks and sensitivity experiments reveal that ecological and biogeochemical changes are driven by a balance between two impacts of a warming climate: higher metabolic rates (the “direct” effect), and changes in the supply of limiting nutrients and altered light environments (the “indirect” effect). On globally integrated productivity, the two effects compensate to a large degree. Regionally, the competition between effects is more complicated; patterns of productivity changes are different between high and low latitudes and are also regulated by how the supply of the limiting nutrient changes. These complex regional patterns are also found in the changes to broad phytoplankton functional groups. On the ï¬ner ecological scale of diversity within functional groups, we ï¬nd that ranges of some phytoplankton types are reduced, while those of others (potentially minor players in the present ocean) expand. Combined change in areal extent of range and in regionally available nutrients leads to global “winners and losers.” The model suggests that the strongest and most robust signal of the warming ocean is likely to be the large turnover in local phytoplankton community composition.

Working Towards a Future on Alternative Fuels: the Role of the Automotive Industry

Complementarity of vehicles and fuels has posed signicant barrier for increasing the use of alternative fuels in place of traditional ones. An initial positive number of either alternative fuel vehicle (AFV) users or alternative fueling stations are needed for the diusion of both. This research examines the incentive of the automotive industry, in particular automobile companies focusing on AFVs, to create a positive number of AFV users by demand-side promotion which increases environmental awareness of consumers, and a positive number of alternative fueling stations by supply-side pro- motion including funding part of the upfront or operating costs of alternative fueling stations. I rst build a static microeconomic model of the vehicle and fuel market and nd that the demand-side promotion is helpful in creating a positive number of AFVs and alternative fueling stations under a wider range of situations than is supply-side promotion. AFV companies are found to have incentive to do these promotions given aordable promotion costs. Furthermore, using data on vehicle purchase and char- acteristics of U.S. consumer units from 2005 to 2010 merged with information on state-level fuel prices, fueling stations, and designation of clean cities, I nd that the addition of 1 clean city or 100 refueling stations of E85, an alternative fuel used in ex-fuel vehicles, is equivalent to a reduction of $0.04 or $0.19 in the E85 price on the eect of increasing ex-fuel vehicle choice probability respectively. Both the theoreti- cal and empirical results suggest that AFV companies evaluate business opportunities in supply- and demand-side promotions, and that policy makers consider potential contributions of the market to bringing about a future on alternative fuels.

WRS-US Version 2 - Technical Note

The MIT Water Resource System for the U.S. (WRS-US) component of the Integrated Global System Model (IGSM) framework is modified to be more computationally efficient and more flexible. For this purpose, version 2.0 of the WRS-US model now solves all basins, or Assessment Sub Regions (ASR), simultaneously. Additionally, the model now includes two objective functions and a new calculation procedure is now adopted to estimate initial storage capacity.

MIT Global Change

JP

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