Summary: The electrification of private cars and light trucks—the vast majority of which are now powered by internal combustion engines (ICEs)—will be critical to efforts to keep global warming well below 2°C or 1.5°C, the long-term goals of the Paris Agreement. Replacing today’s fleet of gasoline and diesel ICEs with plug-in hybrid (PHEV) and battery (BEV) electric vehicles (EVs) could practically eliminate emissions from these light-duty vehicles as part of a broader strategy to decarbonize the transportation sector.

To better understand the potential impact of electric vehicle deployment on total global carbon dioxide emissions, MIT Joint Program researchers enhanced the MIT Economic Projection and Policy Analysis (EPPA) model to represent the fleet dynamics of light-duty vehicles (LDVs) including ICEs, PHEVs and BEVs. Using the enhanced model, they projected global and regional LDV emissions under different climate policy scenarios between the years 2015 and 2050.

The study considered a range of increasingly stringent policy scenarios, from a reference scenario that excludes national pledges delineated in the Paris Agreement to one aligned with the accord’s long-term 2°C goal. The researchers found that as the number of global LDVs grows from 1.1 billion to 1.6-1.8 billion between 2015 and 2050, EV units increase from 1 million to 585-825 million, and thus account for one-third (reference scenario) to one-half (2°C scenario) of the global LDV fleet. Even as the global LDV fleet grows by about 50 percent over the study period, total fleet CO₂ emissions decline by about 50 percent under the 2°C scenario (compared to 10 percent in the reference scenario).

The study suggests that the electrification of light-duty vehicles could play an important role in broader efforts to mitigate global climate change, and highlights the caliber of insights that can be gained from including more precise representation of electric vehicle fleet dynamics in economy-wide energy-economic models.

Abstract: In this study, we present results from a large ensemble of projected changes in seasonal precipitation and near-surface air temperature changes for the nation of South Africa.

The ensemble is based on a combination of pattern-change responses derived from the Coupled Model Intercomparison Project Phase 5 (CMIP-5) climate models along with the Massachusetts Institute of Technology Integrated Global Systems Model (MIT-IGSM), an intermediate complexity earth-system model coupled to a global economic model that evaluates uncertainty in socio-economic growth, anthropogenic emissions, and global environmental response. Numerical experimentation with the MIT-IGSM considered four scenarios of future climate and socio-economic development to span a range of possible global actions to abate greenhouse gas emissions through the 21st century. We evaluate distributions of surface-air temperature and precipitation change over three regions across South Africa: western (WSoAfr), central (CSoAfr), and eastern (ESoAfr) South Africa.  

In all regions, by mid-century, we find a strong likelihood (greater than 50%) that temperatures will rise considerably higher than the current climate’s range of variability 
(a threefold increase over the current climate’s two-standard deviation range of variability). In addition, scenarios that consider more aggressive global climate targets (e.g. 2C and 15C scenarios) all but eliminate the risk of these acutely salient temperature increases. For precipitation, there is a preponderance of risk toward decreased precipitation (3 to 4 times higher than increased) for western and central parts of South Africa.

There is a clear benefit seen within the evolving hydroclimatic risks as a result of strong climate targets, such as limiting the global climate warming to 1.5˚C by 2100. We find that the risk of precipitation changes in the 15C scenario toward the end of this century (2065–2074) is nearly identical to that seen in the REF scenario during the 2030s. Thus, the climate risk that may be experienced in a decade as a result of current global actions to reduce emissions could be delayed by 30 years, and would provide invaluable lead-time for national efforts to be put in place to prepare, fortify, and/or adapt to these changing environments of risk.

Abstract: The shale gas boom in the U.S. has lowered the U.S. CO₂ emissions in recent years mainly through substitution of gas for coal in power generation. Will the shale gas boom reduce the emissions in the long-run as well?

To study this, we consider a counterfactual without the shale gas boom based on a general equilibrium modeling for the 2011 U.S. economy. To enhance the power sector modeling, the supply responses of coal-fired and gas-fired generations are calibrated to existing research. We find that if gas prices remain at 2007 levels in 2011, only a model setting that allows very little reduction in electricity demand, reflecting a short-run demand response, generates an increase in economy-wide emissions. For all other cases, the higher gas price under the counterfactual will have a dampening effect on economic activities and consequently lowers economy-wide emissions, even though the power sector emissions may increase due to the gas-to-coal switch.

In other words, without any policy intervention, although the shale gas boom could reduce emissions in the short run, it may lead to higher emissions in the long run if the low gas prices persist. Our finding suggests that extrapolating the current decline in emissions due to the shale gas boom to the distant future could be misleading. Instead, if curbing emissions is the goal, rather than depending upon the cheap gas, policies and measures for cutting emissions remain imperative.