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The energetic implications of curtailing versus storing solar- and wind-generated electricity
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We present a theoretical framework to calculate how storage affects the energy return on energy
investment (EROI) ratios of wind and solar resources. Our methods identify conditions under which it is
more energetically favorable to store energy than it is to simply curtail electricity production.
Electrochemically based storage technologies result in much smaller EROI ratios than large-scale
geologically based storage technologies like compressed air energy storage (CAES) and pumped
hydroelectric storage (PHS). All storage technologies paired with solar photovoltaic (PV) generation yield
EROI ratios that are greater than curtailment. Due to their low energy stored on electrical energy
invested (ESOIe) ratios, conventional battery technologies reduce the EROI ratios of wind generation
below curtailment EROI ratios. To yield a greater net energy return than curtailment, battery storage
technologies paired with wind generation need an ESOIe > 80. We identify improvements in cycle life as
the most feasible way to increase battery ESOIe. Depending upon the battery's embodied energy
requirement, an increase of cycle life to 10 000–18 000 (2–20 times present values) is required for
pairing with wind (assuming liberal round-trip efficiency [90%] and liberal depth-of-discharge [80%]
values). Reducing embodied energy costs, increasing efficiency and increasing depth of discharge will
also further improve the energetic performance of batteries. While this paper focuses on only one
benefit of energy storage, the value of not curtailing electricity generation during periods of excess
production, similar analyses could be used to draw conclusions about other benefits as well
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The Evolution and Distribution of Species Body Size
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The distribution of species body size within taxonomic groups exhibits a heavy right tail extending over many orders of magnitude, where most species are much larger than the smallest species. We provide a simple model of cladogenetic diffusion over evolutionary time that omits explicit mechanisms for interspecific competition and other microevolutionary processes, yet fully explains the shape of this distribution. We estimate the model’s parameters from fossil data and find that it robustly reproduces the distribution of 4002 mammal species from the late Quaternary. The observed fit suggests that the asymmetric distribution arises from a fundamental trade-off between the short-term selective advantages (Cope’s rule) and long-term selective risks of increased species body size in the presence of a taxon-specific lower limit on body size
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The evolution of growth rates on an expanding range edge
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Individuals in the vanguard of a species invasion face altered selective conditions when compared with conspecifics behind the invasion front. Assortment by dispersal ability on the expanding front, for example, drives the evolution of increased dispersal, which, in turn, leads to accel- erated rates of invasion. Here I propose an additional evolutionary mechanism to explain accelerating invasions: shifts in population growth rate (r). Because individuals in the van- guard face lower population density than those in established populations, they should (relative to individuals in established populations) experience greater r-selection. To test this possibility, I used the ongoing invasion of cane toads (Bufo marinus) across northern Australia. Life-history theory shows that the most efficient way to increase the rate of population growth is to reproduce earlier. Thus, I predict that toads on the invasion front will exhibit faster individual growth rates (and thus will reach breeding size earlier) than those from older populations. Using a common garden design, I show that this is indeed the case: both tadpoles and juvenile toads from frontal popu- lations grow around 30 per cent faster than those from older, long established populations. These results support theoretical predictions that r increases during range advance and highlight the importance of understanding the evolution of life history during range advance.
Keywords: Bufo marinus; invasive species; Rhinella marina; r-selection
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The False Spring of 2012, Earliest in North American Record
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2nd paragraph: As global climate warms, increasingly warmer springs may combine with the random climatological occurrence of advective freezes, which result from cold air moving from one region to another, to dramatically increase the future risk of false springs, with profound ecological and economic consequences [e.g., Gu et al., 2008; Marino et al., 2011; Augspurger, 2013]. For example, in the false spring of 2012, an event embedded in long-term trends toward earlier spring [e.g., Schwartz et al., 2006], the frost damage to fruit trees totaled half a billion dollars in Michigan alone, prompting the federal government to declare the state a disaster area [Knudson, 2012].
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The floodplain large-wood cycle hypothesis: A mechanism for the physical and biotic structuring of temperate forested alluvial valleys in the North Pacific coastal ecoregion
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A ‘floodplain large-wood cycle’ is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested alluvial river valleys of the Pacific coastal temperate rainforest of North America. In the cycle, pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams, which in turn create alluvial patches and protect them from erosion. These stable patches provide sites for trees to ma- ture over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer, thus providing a future source of large wood and reinforcing the cycle. Different tree species can function in the floodplain large-wood cycle in different ecological regions, in different river valleys within regions, and within individual river valleys in which forest composition changes through time. The cycle promotes a physically complex, biodiverse, and self-reinforcing state. Conversely, loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity. Reestablishing large trees is thus necessary to restore such rivers. Although interactions and mechanisms may differ between biomes and in larger or smaller rivers, available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone. Wood debris Riparian forest Fluvial geomorphology Foundation species Biogeomorphology River restoration
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The floodplain large-wood cycle hypothesis: A mechanism for the physical and biotic structuring of temperate forested alluvial valleys in the North Pacific coastal ecoregion
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A ‘floodplain large-wood cycle’ is hypothesized as a mechanism for generating landforms and influencing river dynamics in ways that structure and maintain riparian and aquatic ecosystems of forested alluvial river valleys of the Pacific coastal temperate rainforest of North America. In the cycle, pieces of wood large enough to resist fluvial transport and remain in river channels initiate and stabilize wood jams, which in turn create alluvial patches and protect them from erosion. These stable patches provide sites for trees to ma- ture over hundreds of years in river valleys where the average cycle of floodplain turnover is much briefer, thus providing a future source of large wood and reinforcing the cycle. Different tree species can function in the floodplain large-wood cycle in different ecological regions, in different river valleys within regions, and within individual river valleys in which forest composition changes through time. The cycle promotes a physically complex, biodiverse, and self-reinforcing state. Conversely, loss of large trees from the system drives landforms and ecosystems toward an alternate stable state of diminished biogeomorphic complexity. Reestablishing large trees is thus necessary to restore such rivers. Although interactions and mechanisms may differ between biomes and in larger or smaller rivers, available evidence suggests that large riparian trees may have similarly fundamental roles in the physical and biotic structuring of river valleys elsewhere in the temperate zone.
Dead wood; woody debris; stream; river; habitat; fish
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The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss
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We discuss the existence of cryospheric “tipping points” in the Earth’s climate system. Such critical thresholds have been sug- gested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice–albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such thresh- old behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arc- tic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea- ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.
Greenland | West Antarctic | climate change | tipping point | Arctic
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The Genetic Architecture of Maize Flowering Time
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Flowering time is a complex trait that controls adaptation of plants to their local environment in
the outcrossing species Zea mays (maize). We dissected variation for flowering time with a set of
5000 recombinant inbred lines (maize Nested Association Mapping population, NAM). Nearly a
million plants were assayed in eight environments but showed no evidence for any single largeeffect
quantitative trait loci (QTLs). Instead, we identified evidence for numerous small-effect QTLs
shared among families; however, allelic effects differ across founder lines. We identified no
individual QTLs at which allelic effects are determined by geographic origin or large effects for
epistasis or environmental interactions. Thus, a simple additive model accurately predicts flowering
time for maize, in contrast to the genetic architecture observed in the selfing plant species rice
and Arabidopsis.
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The Global Extent and Determinants of Savanna and Forest as Alternative Biome States
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Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states.
However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting
for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is
globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to
2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire
differentiates between savanna and forest. These may be alternative states over large areas, including
parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to
fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
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The Global Plight of Pollinators
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Wild pollinators are in decline, and managed
honeybees cannot compensate for their loss.
29 MARCH 2013 VOL 339 SCIENCE
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