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 similar to 26.4 to 27.3 My. We performed circular spectral analysis and Fourier transform analysis of the ages of the ten recognised tetrapod-extinction events, and detected a statistically significant (99% confidence) underlying periodicity of similar to 27.5 My. We also find that the eight coeval non-marine/marine-extinction pulses all occurred at the times of eruptions of Large Igneous Provinces (LIPs) (continental flood-basalts and oceanic plateaus), with potentially severe environmental effects. Three of these co-extinction episodes are further correlated with the ages of the three largest (>= 100-km diameter) impact craters of the last 260 My, which are also apparently capable of causing extinction events. These findings suggest that global cataclysmal events with an underlying periodicity of similar to 27.5 My were the cause of the coordinated periodic extinction episodes of non-marine tetrapods and marine organisms.

When wind turbines are arranged in clusters, their performance is mutually affected, and their 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-limit power density in the order of 1 W/m2 and wakes that can extend several tens of kilometers. Here, we address two important questions: 1) How large can a wind farm be before its generation reaches energy replenishment limits and 2) How far apart must large wind farms be spaced to avoid inter-wind-farm interference? We characterize controls on these spatial and temporal scales by running a set of idealized atmospheric simulations using the Weather and Research Forecasting model. Power generation and wind speed within and over the wind farm show that a timescale inversely proportional to the Coriolis parameter governs such transition, and the corresponding length scale is obtained by multiplying the timescale by the geostrophic wind speed. A geostrophic wind of 8 m/s and a Coriolis parameter of 1.05 x 10-4 rad/s (latitude of similar to 46 degrees) would give a transitional scale of about 30 km. Wind farms smaller than this result in greater power densities and shorter wakes. Larger wind farms result instead in power densities that asymptotically reach their minimum and wakes that reach their maximum extent.

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 solar supply and electricity demand for California (CA) and the Western Interconnect (WECC). We quantify the occurrence of resource droughts when the daily power from each resource was less than half of the 39-year daily mean for that day of the year. Averaged over 39 years, CA experienced 6.6 days of solar and 48 days of wind drought per year, compared to 0.41 and 19 for WECC. Using a macro-scale electricity model, we evaluate the potential for both long-term storage and more geographically diverse generation resources to minimize system costs. For wind-solar-battery electricity systems, meeting California demand with WECC generation resources reduces the cost by 9% compared to constraining resources entirely to California. Adding long-duration storage lowers system costs by 21% when treating California as an island. This data-driven analysis quantifies rare weather-related events and provides an understanding that can be used to inform stakeholders in future electricity systems.

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 GaussVanicek method of spectral analysis, fails to find a significant 27.5 My cycle in the same data. He claims to find predominant short (< 1 My) Earth precession cycles in the data set, where the smallest interval between extinction events is 8 My. In response to Omerbashich, we performed a new analysis of non-marine extinctions using a best-fit method that again displays the high spectral peak at similar to 27.5 My.

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 optimization framework taking into account technoeconomic factors only, considering electricity demand and renewable potential in 42 country-level regions. In our model, in moderate decarbonization scenarios, solar and wind can provide less costly electricity when competing against nuclear at near-current US Energy Information Administration (US$6,317 per kilowatt-electric (kWe)) and at US$4,000 kWe(-1) cost levels. In contrast, in deeply decarbonized systems (for example, beyond similar to 80% emissions reduction) and in the absence of low-cost grid-flexibility mechanisms, nuclear can be competitive with solar and wind. High-quality wind resources can make it difficult for nuclear to compete. Thermal heat storage coupled to nuclear power can, in some cases, promote wind and solar.

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 electric vehicle (EV) penetration using Nigeria as a case study. Results indicate that, despite Nigeria having a natural gas-dominated electricity system, the deployment of EVs can support the decarbonization of the transportation and power sectors but at a relatively high cost. The cost of EVs would need to drop by similar to 40% to become cost-competitive. However, if variable renewable energy sources deliver the EVs power requirement with a bidirectional vehicle-to-grid (V2G) charging strategy, then the cost of EVs would need to decline by only similar to 30%. Not all EVs need to participate in a V2G charging strategy in order to realize the full benefits of the strategy. Expanding renewables capacity leads to additional reduction in CO2 emission and decarbonization cost but at different magnitudes based on the charging strategy.

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 CO2. In this study, using a set of idealized global climate-carbon model simulations with equal amounts of CO2 emissions, we show that on century to millennial timescales the response of the climate system to fossil-fuel burning versus deforestation disturbance are vastly different. We performed two 1000 year simulations where we add abrupt emissions of about 600 PgC to the preindustrial state as a consequence of either fossil fuel use or deforestation disturbance with vegetation regrowth. In the fossil fuel simulations, after 1000 years, about 20% of the initial atmospheric CO2 concentration perturbation remains in the atmosphere and the climate is about 1 degrees C warmer compared to preindustrial state. In contrast, in the case of deforestation with regrowth, after 1000 years, atmospheric CO2 concentration returns close to preindustrial values, because deforested land will typically recover its carbon over the decades and centuries in the absence of further human intervention. These results highlight the differences in the degree of long-term commitment associated with fossil-fuel versus deforestation emissions.

Solar photovoltaics, with sufficient power generation potential, low-carbon footprint, and rapidly declining costs, could supplant fossil fuels 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 increasing prescribed amounts of solar power. Our results show that there are initially great benefits when providing solar power to the system, especially under deep decarbonization scenarios. The marginal value of additional solar power decreases substantially with increasing cumulative solar capacities. At costs near today's levels, the modeled zero-emission electricity system with free solar generation equaling twice the annual mean demand is more costly than a carbon-emitting natural-gas-based system supplying the same electricity demand with no solar. Taking full advantage of low-cost solar will depend on developing and deploying low-cost approaches to temporally shift either energy supply (e.g., storage) or electricity loads (e.g., load-shifting).

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 carbon emission constraints and substantial amounts of flexible electricity sources on the grid (e.g., dispatchable power), relatively high value is placed on sites with high capacity factors because the added wind or solar capacity can efficiently substitute for running natural gas power plants. With strict carbon emission constraints, relatively high value is placed on sites with high correlation with residual demand because resource complementarity can efficiently compensate for lower system flexibility. Our results suggest that decisions regarding long-term wind and solar farm siting may benefit from consideration of the spatial and temporal evolution of mismatches in electricity demand and generation capacity.