JP

Representing socio-economic uncertainty in human system models

Abstract: Future global socio-economic development pathways and their implications for the environment are highly uncertain, as are the technology mixes associated with different global environmental targets.

To develop a range of possible future outcomes, we develop probability distribution estimates for key input parameters of a model of global human activity. Latin Hypercube Sampling is applied to draw 400 samples from the probability distributions for each uncertain input variable, including costs of advanced energy technologies, energy efficiency trends, fossil fuel resource availability, elasticities of substitution, population, and labor and capital productivity. The sampled values are simulated through a multi-sector, multi-region, recursively dynamic model of the world economy.

The results are 400-member ensemble simulations describing future energy and technology mixes as well as GDP and emissions. We find that many patterns of energy and technology development are consistent with various long-term environmental pathways, and that sectoral output for most sectors is little affected through 2050 by the long-term temperature target, but with tight constraints on emissions, emission intensities must fall much more rapidly.

We also combine uncertainty quantification and scenario discovery to investigate scenarios with similar values for one outcome and the range of other outcomes in those scenarios. This analysis illustrates how many combinations of outcomes can be consistent with an outcome of interest. For example, many different technology outcomes can be consistent with high or low economic growth.

Switching on auxiliary devices in vehicular fuel efficiency tests can help cut CO2 emissions by millions of tons

Abstract: Enhancing automobile fuel efficiency is crucial to decarbonizing the transport sector. Recent studies have revealed a gap between real-world fuel efficiency and results from laboratory tests, where “off-cycle” auxiliary devices, like air conditioning (AC) systems, are not turned on. AC consumes the most energy among all off-cycle devices; however, the exact contribution of AC to fuel consumption remains unclear.

Here, by analyzing 1 million trip-level fuel efficiency records from China, we show that AC use when the temperature exceeds 25°C increases gasoline consumption annually by 1.3%. The amount differs across car models, with those produced by Chinese manufacturers showing relatively lower AC efficiency. Improving AC efficiency could cost-effectively reduce CO2 emissions by 1.6–2.4 million tons in China every year.

Therefore, we suggest integrating off-cycle devices into future fuel efficiency regulations, which will reveal the fuel efficiency gap, incentivize car manufacturers to develop high-efficiency devices, and further tap this emissions reduction potential.

A consistent framework for uncertainty in coupled human-Earth system models

Abstract: Addressing climate change is ultimately a challenge of risk management, which requires an understanding of the likelihood of potential outcomes. We provide integrated, probabilistic socio-economic and climate projections obtained using updated estimates of probability distributions for key parameters in both the human and Earth system components of the MIT Integrated Global System Model (IGSM).

The Reference scenario results in median end-of-century warming of 3.5oC and a 90% range of 2.8-4.3oC, which is lower than the median of 5.7oC from a prior study using a previous version of the IGSM. About 0.5oC of the difference is due to updated estimates in the human system and the rest of the difference is explained by changes in Earth system estimates.

Our results show that climate policy lowers the upper tail of temperature change distributions more than the median, and that even relatively modest policies can significantly reduce the likelihood of high global temperature outcomes. Human system uncertainties contribute more to uncertainty in projected CO2 concentrations and total radiative forcing, while Earth system uncertainties have the greatest influence on temperature and precipitation. Including additional uncertain inputs does not automatically increase the outcome range because uncertainties can offset one another.

Results also show how policy costs can vary greatly among regions.  As we improve understanding of underlying technology and economic factors as well as Earth system response to human forcing, further updating of these estimates of uncertainty can make an important contribution to decision-making about mitigation and adaptation.

Methyl Chloroform continues to constrain the hydroxyl (OH) variability in the troposphere

Abstract: Trends and variability in tropospheric hydroxyl (OH) radicals influence budgets of many greenhouse gases, air pollutant species and ozone depleting substances. Estimations of tropospheric OH trends and variability based on budget analysis of methyl chloroform (CH3CCl3), and process‐based chemistry transport models often produce conflicting results. Here we use a previously tested transport model to simulate atmospheric CH3CCl3 for the period 1985‐2018. Based on mismatches between model output and observations, we derive consistent anomalies in the inverse lifetime of CH3CCl3 (KG) using measurements from two independent observational networks (NOAA and AGAGE). Our method allows a separation between “physical” (transport, temperature) and “chemical” (i.e., abundance) influences on OH+CH3CCl3 reaction rate in the atmosphere. Small increases in KG due to “physical” influences are mostly driven by increases in the temperature‐dependent reaction between OH and CH3CCl3 and resulted in a smoothly varying increase of 0.80 % decade‐1 . Chemical effects on KG, linked to global changes in OH sources and sinks, show larger year‐to‐year variations (∼2‐3%), and have a negative correlation with the El Niño Southern Oscillation. A significant positive trend in KG can be derived after 2001, but it persists only through 2015 and only if we assume that CH3CCl3 emissions decayed more slowly over time than our best estimate suggests. If global CH3CCl3 emissions dropped below 3 Gg yr‐1 after 2015, recent CH3CCl3 measurements indicate that the 2015‐2018 loss rate of CH3CCl3 due to reaction with OH is comparable to its value two decades ago.

Many world regions face increasing pressures from global and regional changes in climate, population growth, urban-area expansion, and the socio-economic impacts of fossil-based development. Human interference in the global climate system contributes significantly to changes in regional and local extreme weather and climate patterns.

ILP-MIT Joint Program Workshop/Webinar: Climate-Related Physical and Transition Risks

The energy sector is facing unprecedented challenges, with the global Covid-19 pandemic complicating an already challenging transition toward a low-carbon future. One of the key elements in addressing both the current pandemic and climate change is with forward-looking collaborations in technology development and innovation—which have long been a hallmark of MIT’s approach to problem solving.

ILP-MITEI WEBINAR: Scaling up low-carbon energy: Economic, geopolitical, and environmental impacts

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