Ken Caldeira

Gates Ventures LLC

Resource adequacy, or ensuring that electricity supply reliably meets demand, is more challenging for wind-and solar-based electricity systems than fossil-fuel-based ones. Here, we investigate how the number of years of past weather data used in designing least-cost systems relying on wind, solar, and energy storage affects resource adequacy. We fi...

In contrast to battery storage systems, power-to-hydrogen-to-power (P-H2-P) storage systems provide opportunities to separately optimize the costs and efficiency of the system’s charging, storage, and discharging components. The value of capital cost reduction relative to round-trip efficiency improvements of P-H2-P systems is not well understood i...

Understanding the climate and carbon cycle response to negative CO2 emissions is important for developing climate mitigation strategies that aim to limit global warming to a specific threshold. In this study, using a coupled climate and carbon cycle model, a novel set of nine stylized simulations are conducted with cumulative emissions of 1,000 GtC...

A stylized macro-scale energy model of least-cost electricity systems relying only on wind and solar generation was used to assess the value of different storage technologies, individually and combined, for the contiguous U.S. as well as for four geographically diverse U.S. load-balancing regions. For the contiguous U.S. system, at current costs, w...

Wind droughts, or prolonged periods of low wind speeds, pose challenges for electricity systems largely reliant on wind generation. Using weather reanalysis data,we analyzed the global distribution of and trends in wind droughts using an energy deficit metric that integrates the depth and duration of wind droughts. We identified regions with high p...

‘Firming’ technologies can be coupled to variable wind and solar generation to meet electricity demand reliably. Options that could participate in this firming role include dispatchable electricity generators, electricity storage technologies, atmospheric carbon dioxide removal, and demand management. In this study, we allow various firming technol...

Plans for decarbonized electricity systems rely on projections of highly uncertain future technology costs. We use a stylized model to investigate the influence of future cost uncertainty, as represented by different projections in the National Renewable Energy Laboratory 2021 Annual Technology Baseline dataset, on technology mixes comprising least...

Efforts to make food systems more sustainable have emphasized reducing adverse environmental impacts of agriculture. In contrast, chemical and biological processes that could produce food without agriculture have received comparatively little attention or resources. Although there is a possibility that someday a wide array of attractive foods could...

The 2022 Indus floods in Pakistan underscore the urgency of adapting to more frequent and severe natural disasters in a warming world. Post-disaster reconstruction offers a chance to built-in adaptation measures, but identifying feasible and cost-effective adaptation options is challenging, especially in data-scarce regions. Here we employ a high-r...

Carbon-emitting technologies often cost less than carbon-emission-free alternatives; this difference in cost is known as the Green Premium. Innovations that decrease the Green Premium contribute to achieving climate goals, but a conceptual framework to quantify that contribution has been lacking. Here, we devise a framework to translate reductions...

Proposals for achieving net-zero emissions by 2050 include scaling-up electrolytic hydrogen production, however, this poses technical, economic, and environmental challenges. One such challenge is for policymakers to ensure a sustainable future for the environment including freshwater and land resources while facilitating low-carbon hydrogen produc...

In this commentary, we provide additional context for Ocko and Hamburg (2022) related to the climate consequences of replacing fossil fuels with clean hydrogen alternatives. We first provide a tutorial for the derivations of underlying differential equations that describe the radiative forcing of hydrogen emissions, which differ slightly from equat...

Stratospheric Aerosol Geoengineering (SAG) is one of the solar geoengineering approaches that have been proposed to offset some of the impacts of anthropogenic climate change. Past studies have shown that SAG may have adverse impacts on the global hydrological cycle. Using a climate model, we quantify the sensitivity of the tropical monsoon precipi...

Scale up of electrolytic production of hydrogen has been proposed as key to achieving net-zero emissions by 2050. This poses technical, economic, and environmental challenges. One challenge concerns the use of wind and solar resources to power water electrolyzers for low-carbon hydrogen production, which results in additional demand for already sca...

In this commentary, we provide additional context for Ocko and Hamburg (2022) related to the climate consequences of replacing fossil fuels with clean hydrogen alternatives. To develop a better understanding of the climate impact from atmospheric hydrogen additions, we first provide a step-by-step tutorial for the derivations of underlying differen...

We employed an idealized macro-energy system model to examine how the value of unidirectional and bidirectional charging electric vehicles (EVs) varies with EV penetration and mix of electricity generators. We find that EVs can help wind and solar-based electricity generation systems to be less costly by making better use of power that would otherw...

Transportation contributes about 24% of total global carbon emissions from fossil fuel combustion (IEA 2020). To decarbonize the transportation sector in support of global climate action, electric vehicles (EVs) will play a key role (Coignard et al 2018, Taljegard et al 2019, Muratori 2021, Dioha et al 2022). The total number of EVs on the world's...

Carbon dioxide emissions from deforestation disturbance (e.g., clear-cutting, forest fires) are in the same units as carbon dioxide emissions from fossil fuels. However, if the forest is allowed to regrow, there is a large difference between climate effects of that forest disturbance and climate effects of fossil CO 2 . In this study, using a set o...

New designs of advanced nuclear power plants have been proposed that may allow nuclear power to be less expensive and more flexible than conventional nuclear. It is unclear how and whether such a system would complement variable renewables in decarbonized electricity systems. Here we modelled stylized electricity systems under a least-cost optimiza...

Policies in the US increasingly stipulate the use of variable renewable energy sources, which must be able to meet electricity demand reliably and affordably despite variability. The value of grid services provided by additional marginal capacity and storage in existing grids is likely very different than their value in a 100% variable renewable el...

Solar photovoltaics, with sufficient power generation potential, low-carbon footprint, and rapidly declining costs, could supplant fossil fuel uses and help produce lower-cost net-zero emissions energy systems. Here we used an idealized linear optimization model, including free lossless transmission, to study the response of electricity systems to...

Wind and solar photovoltaic generators are projected to play important roles in achieving a net-zero-carbon electricity system that meets current and future energy needs. Here, we show potential advantages of long-term site planning of wind and solar power plants in deeply decarbonized electricity systems using a macro-scale energy model. With weak...

Over the past two decades, the United Nations, the World Bank, regional development banks, and national governments have led efforts to give more people access to electricity. The movement has made significant gains: in Asia alone, about 1.2 billion people have gained electricity access since 2000. Still, these initiatives to extend energy access g...

We employed a bottom-up modeling framework to examine a set of scenarios to generate insights on the techno-economic and environmental implications of increasing levels of EV penetration using Nigeria as a case study. Results indicate that, despite having a natural gas-dominated electricity system, the deployment of EVs can support the decarbonizat...

Electricity systems worldwide are transforming from relying almost exclusively on firm, predictable generation (e.g., fossil, nuclear, and large hydropower) towards incorporating more variable generation (e.g., wind and solar PV). In these systems, the electric load minus generation from variable resources is known as the “residual load.” The peak...

When wind turbines are arranged in clusters, their performance is mutually affected, and the energy generation is reduced relative to what it would be if they were widely separated. Land-area power densities of small wind farms can exceed 10 W/m2 and wakes are several rotor diameters in length. In contrast, large-scale wind farms have an upper-limi...

Wind and solar photovoltaic are projected to play important roles in achieving a net-zero-carbon electricity system that meets current and future energy needs. Here, we show potential advantages of long-term site planning of wind and solar power plants in deep decarbonization scenarios for electricity systems. We use a macro-scale energy model to f...

Electric sector capacity expansion models are widely used by academic, government, and industry researchers for policy analysis and planning. Many models overlap in their capabilities, spatial and temporal resolutions, and research purposes, but yield diverse results due to both parametric and structural differences. Previous work has attempted to...

We performed spectral analyses on the ages of 89 well-dated major geological events of the last 260 Myr from the recent geologic literature. These events include times of marine and non-marine extinctions, major ocean-anoxic events, continental flood-basalt eruptions, sea-level fluctuations, global pulses of intraplate magmatism, and times of chang...

Hundreds of gigawatts of renewable technologies, such as wind and solar, need to be installed to reach a zero-carbon electricity system that meets current and future energy needs. Locations of new installations are typically chosen based on wind and solar availability to maximize facilities’ capacity factors. Here, we show that this is not always t...

If future net-zero emissions energy systems rely heavily on solar and wind resources, spatial and temporal mismatches between resource availability and electricity demand may challenge system reliability. Using 39 years of hourly reanalysis data (1980–2018), we analyze the ability of solar and wind resources to meet electricity demand in 42 countri...

Wind and solar electricity generation is projected to expand substantially over the next several decades due both to rapid cost declines as well as regulation designed to achieve climate targets. With increasing reliance on wind and solar generation, future energy systems may be vulnerable to previously underappreciated synoptic-scale variations ch...

Variability of wind and solar generation and electricity demand poses substantial challenges to the affordable supply of reliable electricity. In a modeling study published in Energy & Environmental Science, Guerra and colleagues find that a portfolio of energy storage technologies provides the least-cost path to reliable electricity supply.

Significance Wind comprised 6.1% of worldwide electricity generation in 2020. If this share is to substantially grow to decarbonize electricity systems, the size of future wind farms may extend far beyond that of current installations. The spatial scale of a wind farm affects both its mean generation per unit of land and the extension of wake shado...

Variable, low-cost, low-carbon electricity that would otherwise be curtailed may provide a substantial economic opportunity for entities that can flexibly adapt their electricity consumption. We used historical hourly weather data over the contiguous U.S. to model the characteristics of least-cost electricity systems dominated by variable renewable...

Wind and solar electricity generation is projected to expand substantially over the next several decades due both to rapid cost declines as well as regulation designed to achieve climate targets. With increasing reliance on wind and solar generation, future energy systems may be vulnerable to previously underappreciated synoptic-scale variations ch...

As reliance on wind and solar power for electricity generation increases, so does the importance of understanding how variability in these resources affects the feasible, cost-effective ways of supplying energy services. We use hourly weather data over multiple decades and historical electricity demand data to analyze the gaps between wind and sola...

Our circular-spectral and Fourier analyses of the ages of the 10 recognized non-marine tetrapod extinction events over the last 300 My revealed a significant spectral peak at 27.5 My. Omerbashich, using his Gauss-Vaniçek method of spectral analysis, fails to find a significant 27.5 My cycle in the same data. He claims to find predominant short (< 1...

Can we engineer our way out of the planetary problems we've engineered our way into?

Global and local anthropogenic stressors such as climate change, acidification, overfishing, and pollution are expected to shift the benthic community composition of coral reefs from dominance by calcifying organisms to dominance by non‐calcifying algae. These changes could reduce the ability of coral reef ecosystems to maintain positive net calciu...

Solar radiation modification has been suggested as a backup option to reduce anthropogenic warming. Marine cloud brightening (MCB) and ocean albedo modification (OAM) are two proposed approaches to intentionally reflect sunlight back to space over oceanic regions. Using the NCAR Community Earth System Model, we compare climate response to MCB and O...

The geophysical limit to maximum land-area power density of large wind farms is related to the rate of replenishment of kinetic energy removed from the atmosphere by wind turbines. Although observations and numerical simulations have indicated an upper bound to the power density in the order of 1 W/m2, no theoretical foundation has yet been provide...

The extraction of energy from the atmosphere by large wind farms is limited by its potential availability and replenishment rate. Although observations and numerical simulations have indicated an upper bound to the power density in the order of 1 W/m , no theoretical foundation has yet been provided. Here, we study the role of atmospheric pressure...

Non-marine tetrapods (amphibians, reptiles, birds and mammals) have apparently experienced at least 10 distinct episodes of intensified extinctions over the past 300 My. Eight of these ten non-marine extinction events are concurrent with known marine-extinction episodes, which previously yielded evidence for an underlying period of ~26.4 to 27.3 My...

To reduce atmospheric carbon dioxide emissions and mitigate impacts of climate change, countries across the world have mandated quotas for renewable electricity. But a question has remained largely unexplored: would low-cost, firm, zero-carbon electricity generation technologies enhance—or would they displace—deployment of variable renewable electr...

Decarbonizing the energy system is a major challenge facing the richest countries, whereas provision of energy services is a major challenge facing the poorest countries. What would be the climate consequences if only richer countries focus on decarbonization, and only poorer countries focus on provision of energy services? To address this question...

Human migration is both motivated and constrained by a multitude of socioeconomic and environmental factors, including climate-related factors. Climatic factors exert an influence on local and regional population density. Here, we examine the implications of future motivation for humans to migrate by analyzing today's relationships between climatic...

Facing severe air pollution issues, China has implemented a series of clean air policies aimed to improve the country's air quality. These policies largely focused on reducing emissions of major air pollutants such as sulfur dioxide (SO2) and primary aerosols. However, changes in such pollution also affect radiative forcing. To understand the clima...

Global climate change mitigation is often framed in public discussions as a tradeoff between environmental protection and harm to the economy. However, climate-economy models have consistently calculated that the immediate implementation of greenhouse gas emissions restriction (via e.g. a global carbon price) would be in humanity’s best interest on...

Reliable and affordable electricity systems based on variable energy sources, such as wind and solar may depend on the ability to store large quantities of low-cost energy over long timescales. Here, we use 39 years of hourly U.S. weather data, and a macro-scale energy model to evaluate capacities and dispatch in least cost, 100% reliable electrici...

We use 36 years (1980-2015) of hourly weather data over the contiguous United States (CONUS) to assess the impact of low-cost energy storage on highly reliable electricity systems that use only variable renewable energy (VRE; wind and solar photovoltaics). Even assuming perfect transmission of wind and solar generation aggregated over CONUS, energy...

Spectral analyses of past relative sea-level oscillations as represented by the ages of 57 Phanerozoic (the last 545 Myr) stratigraphic sequence boundaries from the Canadian Arctic show a strong spectral peak at 32 Myr (>99.9% confidence). These findings concur with previous reports of significant cycles with periods of around 30 Myr in various rec...

Abstract Global mean surface air temperature (Tglobal) variability on subdecadal timescales can be of substantial magnitude relative to the long‐term global warming signal, and such variability has been associated with considerable environmental and societal impacts. Therefore, probabilistic foreknowledge of short‐term Tglobal evolution may be of v...

Electricity usage (demand) data are used by utilities, governments, and academics to model electric grids for a variety of planning (e.g., capacity expansion and system operation) purposes. The U.S. Energy Information Administration collects hourly demand data from all balancing authorities (BAs) in the contiguous United States. As of September 201...

A number of radiation modification approaches have been proposed to counteract anthropogenic warming by intentionally altering Earth's shortwave or longwave fluxes. While several previous studies have examined the climate effect of different radiation modification approaches, only a few have investigated the carbon cycle response. Our study examine...

The climate effects of anthropogenic aerosols have masked some of the warming induced by GHGs1 along with some impacts of that warming2. These temperature effects may be beneficial but are almost certainly overwhelmed by aerosols’ negative health impacts3. Recent analyses of economic impacts have concluded that warming harms economies in warm clima...

Understanding the extent to which laboratory findings of low pH on marine organisms can be extrapolated to the natural environment is key towards making better projections on the impacts of global change on marine ecosystems. We simultaneously exposed larvae of the sea urchin Arbacia lixula to ocean acidification in laboratory and natural CO2 vents...

Abstract Solar geoengineering by deliberate injection of sulfate aerosols in the stratosphere is one of the proposed options to counter anthropogenic climate warming. In this study, we focus on the effect of a specific microphysical property of sulfate aerosols in the stratosphere: hygroscopic growth—the tendency of particles to grow by accumulatin...

The relationship between cnidarians and their micro-algal symbionts is crucial for normal animal function and the formation of coral reefs. We used the sea anemone Exaiptasia pallida (Aiptasia) as a model cnidarian–dinoflagellate system to determine the effects of white, blue and red light on photo-movement. In white light, phototropism and photota...