Selected Publications
Drivers of CO2 emissions from road transport in U.S. urban areas
The drivers of CO₂ emissions from road transportation and differences among U.S. cities are not well-understood owing to limited availability of detailed data. Here, we use new, high-resolution GPS data of individual vehicles' position and speed to analyze street-specific emissions in 454 U.S. cities in 2022, and show that transportation demand per capita is the dominant cause of city-to-city differences, followed by differences in vehicle fleets, with congestion having the least effect.
Multiregional accounting for corporate carbon emissions
We use a high-resolution multiregional input-output model to show that the upstream emissions of the companies reporting to CDP are together greater by 2.0 gigatons of CO₂-equivalent emissions when estimated by a multiregional model instead of the dominant U.S. single-region model. Widespread adoption of multiregional models could thus improve the accuracy of corporate emissions inventories and help prioritize primary data collection and emissions reduction efforts, often by shifting focus to energy- and emissions-intensive sectors of industrializing nations.
The global hydrogen budget
Although hydrogen (H₂) is a potentially important energy carrier in decarbonized energy systems, its interactions with methane, ozone, and stratospheric water vapor lead to an indirect 100-year global warming potential of 11 ± 4. We analyse trends in global H₂ sources and sinks from 1990 to 2020 and find that both have been increasing. Finally, we estimate that rising atmospheric H₂ 2010-2020 have increased global surface air temperature by ~0.02 °C and project future warming of 0.01–0.05 °C, depending on H₂ usage, leakage rates and CH₄ emissions that influence photochemical H₂ production.
Ownership of power plants stranded by climate mitigation
We use detailed data from 16,438 power plants worldwide to evaluate the scale of financial risks by region, generator type, and corporate ownership. Of the 100 companies that own the most stranded assets by value, the very largest are state-owned, and the top twenty-five companies cumulatively hold upwards of $770 and $224 billion in stranded assets under a 1.5°C and 2.0°C scenarios, respectively.
Global hydroclimatic risks and strategic decommissioning pathways for thermal power units
Increasing water temperatures and water shortages reduce the cooling efficiency of thermal power plants (fossil, nuclear), and thereby energy security. We develop a global, unit-level model to assess such hydroclimatic risks, and find that >60% of thermal power capacity worldwide could see decreased capacity factors by midcentury. In addition, though, we show that thoughtful decommissioning strategies could substantially mitigate these risks.
Economic development, air conditioning and adaptation to warming
We examine how global warming and economic growth together affect exposure to high temperatures without air conditioning. We find that populations in lower-income countries would require GDP growth rates that exceed historical rates to avoid increasing the numbers of days with high temperatures experienced without air conditioning.
Variability of technology learning rates
We analyze the Performance Curve Database of historical observations of unit cost or unit price and cumulative production over time for 135 technologies, and find that while costs generally decrease with increasing production, past learning rates for a given technology are not a good predictor of future learning rates.
Long-range PM2.5 pollution and health impacts from the 2023 Canadian wildfires
We use satellite observations, machine learning and a chemical transport model to estimate the number of deaths worldwide attributable to the Canadian wildfires of 2023. In total, we find that the fires may have caused nearly 90,000 premature deaths, concentrated in the U.S. and Europe--downwind regions with larger populations than Canada itself.
Historical model biases in monthly high temperature anomalies indicate under-estimation of future temperature extremes
We show that over the historical period climate models have underestimated the magnitude high temperature extreme events relative to monthly mean temperatures. If such biases persist into the future, extreme high temperatures in 2100 could exceed current projections by up to 5°C in some regions and months.
Thermal energy storage in dirt for repowering decommissioned coal plants
We find that in systems reliant on wind, solar, and natural gas generation, thermal storage in dirt could play a role in meeting seasonal demand peaks at current costs.
Carbon removal by preservation of woody debris
We show the potential to remove remove >10 Gt of CO2 from the atmosphere annually by preserving woody debris from logging, sawmill wastes and abandoned woody products in deep soil to lengthen its residence time (a measure of durability) for centuries.
Potential of a global grid for solar-wind electricity systems
We use energy system modeling to assess a hypothetical a global electricity transmission system, and quantify benefits for the cost and reliability of solar-wind systems. We find a global grid could reduce system costs and greatly improve resilience to climate extremes, generation outages, transmission disruptions, and geopolitical conflicts.
Trade risks in net-zero emissions energy scenarios
We analyze changes in country-level trade risks in >1000 scenarios that reach net-zero energy emissions, taking into account imports and sources of both energy carriers and materials to meet demand, and find that reductions in fuel-related risks largely offset the increase in material-related risks in more than 70% of countries worldwide, assuming no changes in current trading relationships.
A path to US Tribal energy sovereignty
We explore how Tribal energy resources might be developed to provide Tribal Nations and people with enhanced sovereignty and increased economic well-being while also supporting U.S. energy and security goals.
Potential to store carbon in the built environment
We explore the scale of CO2 that might be stored annually in construction materials, including concrete, brick, asphalt, wood, and plastics, and find that fully replacing these conventional materials with CO2-storing alternatives could sequester >16 Gt of CO2 each year.
Mitigating climate change and ozone pollution will improve Chinese food security
Looking into feedbacks among land-use, agriculture, and climate mitigation, we find that reducing GHG emissions in China would also reduce ozone-related crop losses and could free land to absorb substantial quantities of CO2 each year.
Planning reliable wind- and solar-based electricity systems
We investigated how the number of years of weather data used in designing least-cost systems relying on wind, solar, and energy storage affects resource adequacy. Nearly 40 years of weather data are required to plan systems that experience zero lost load over a decade, but only 15 years of weather data are needed when there is dispatchable generation to supply 5% of electricity demand.
Opportunities and constraints of hydrogen energy storage systems
We modeled the sensitivity of wind-solar-battery electricity system costs to characteristics of hydrogen-based energy storage. Even at current costs, hydrogen energy storage is included in least-cost systems, but we found that the capital costs of such storage represent a key opportunity to minimize curtailment of renewable generation and reduce overall system costs.
Climate change impacts on the reliability of wind-solar resources
We use hourly reanalysis data to examine the trends in periods of low wind and solar resources over the past 40 years, and find that such periods are becoming more frequent, extreme, and longer. Our findings suggest that wind-solar systems may become less reliable in a warmer future.
Drivers of natural gas use in U.S. residential buildings
We use daily, county-level gas consumption data and interpretable machine learning models to assess spatial patterns in natural gas consumption of households as a function of outdoor air temperature, as well as factors such as household income, employment rates, the size, age and type of homes, employment rates, and a range of other characteristics.
Rebound effects could offset more than half of avoided food loss and waste
We model reductions in food loss and waste to show that there could be substantial rebound effects--price decreases and consumption increases—-that would offset some of the benefits of avoided loss and waste.
Food without agriculture
Edible molecules can be directly synthesized without agricultural feedstocks, saving land, water and GHG emissions. Dietary fats made from natural gas feedstock and average U.S. electricity would emit ~0.8 gCO2-eq/kcal (and 0 if using atmospheric carbon and renewable electricity) compared to 1-3 gCO2-eq/kcal from agricultural fat production.
Climate warming increases extreme daily wildfire growth risk in California
We use machine learning to quantify the relationship of temperature and wildfires that grow by >10,000 acres/day in California, finding that human-caused warming has increased the frequency of such wildfire growth by ~25% relative to the preindustrial era, which will further increase to ~59% by 2100 even if warming is kept low (i.e. <2°C).
Pathways to net-zero emissions aviation
We assess nine possible pathways to achieve net-zero emissions from aviation, including changes and trade-offs in demand, energy efficiency, propulsion systems, and alternative fuels for both passenger and freight transport, as well as atmospheric carbon removal to offset non-CO2 radiative forcing.
Materials for electricity in mitigation scenarios
We estimate how many tons of steel, copper, silver, rare earth metals, and other materials will be needed to build power generation facilities across a wide range of scenarios. Although wind and solar energy require lots of such materials and current production will need to increase, availability of metals and materials will not constrain the projected expansion.
Economic and biophysical limits to seaweed farming for climate change mitigation
Global modeling shows that potential climate benefits of farming seaweed are large but sensitive to uncertain yields and competition with phytoplankton. We also find that carbon removal by sinking seaweed is much costlier than avoiding emissions by substituting seaweed for land-based crops.
Large and inequitable flood risks in Los Angeles
Ultra-high-resolution modeling of Los Angeles flood risks reveals risks that are vastly larger than suggested by federally-defined floodplains and with both racial and socio-economic inequalities in exposure. Our approach points to opportunities for assessing and equitably reducing flood risks in densely-populated urban areas.
Land-use emissions embodied in trade
Annually, 27% of land-use emissions are related to agricultural products consumed in a different region from where they were produced. The largest transfers are land-use change emissions from Brazil, Indonesia, and Argentina embodied in products consumed in Europe, the US, and China. Our results highlght the importance of trade in stopping deforestation and making food systems more sustainable.
Cement and steel - nine steps to net-zero
It is possible — and crucial — to green the building blocks of the modern world. We highlight nine priorities for research and action. Steel manufacturing processes need a rethink; cement’s biggest gains will require carbon capture and storage (CCS). Together, these steps could take steel close to being carbon neutral and cement to becoming a carbon sink.
Geophysical constraints on the reliability of solar and wind power worldwide
Analyzing 39 years of hourly weather data across 42 countries, we show that, to a first approximation, the variability of solar and wind resources in a country largely determine how much "overbuilding," long-duration storage, long-distance transmission, and/or firm generation back-up will be necessary.
Global and regional drivers of land-use emissions
We estimate country-, process-, GHG- and product-specific land-use emissions 1961-2017. Total emissions have increased to 14.6 GtCO2-eq in 2017 (~25% of anthropogenic GHG emissions). Our results may help prioritize mitigation efforts, but suggest drastic reductions in emissions will require similarly drastic changes in agricultural production and/or practices.