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"Greene, David"
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Coordinating the electric vehicle transition and electricity grid decarbonization in the U.S. is not essential to achieving substantial long-term carbon dioxide emissions reductions
How quickly the US can decarbonize light-duty vehicle (LDV) transportation depends on the rates of change of electric vehicle (EV) sales, stock turnover, and grid decarbonization. We build a stock turnover model to assess how sensitive achieving 2050 LDV decarbonization targets is to these rates. We estimate carbon dioxide (CO 2 ) reductions of 70%–85% by 2050, including emissions from vehicles and upstream electricity generation, provided that new vehicle sales transition to 100% EVs and substantial grid decarbonization are accomplished by 2050. This result is robust to continuation of long-term trends of increasing vehicle longevity, and to whether the timing of EV sales growth and grid decarbonization are coordinated. If the two key goals are met, the annual contribution of EV electricity use to CO 2 emissions will be small over the entire period.
Journal Article
Midnight in Siberia : a train journey into the heart of Russia
\"After two and a half years as NPR's Moscow bureau chief, David Greene travels across the country--a 6,000-mile journey by rail, from Moscow to the Pacific port of Vladivostok--to speak with ordinary Russians about how their lives have changed in the post-Soviet years. Reaching beyond the headline-grabbing protests in Moscow, Greene speaks with a group of singing babushkas from Buranovo, a teenager hawking 'space rocks' from last spring's meteor shower in Chelyabinsk, and activists battling for environmental regulation in the pollution-choked town of Baikalsk\"--Provided by publisher.
BOOK
An assessment of temporal variability in mast seeding of North American Pinaceae
Our overall objective is to synthesize mast-seeding data on North American Pinaceae to detect characteristic features of reproduction (i.e. development cycle length, serotiny, dispersal agents), and test for patterns in temporal variation based on weather variables. We use a large dataset (𝑛 = 286 time series; mean length = 18.9 years) on crop sizes in four conifer genera (Abies, Picea, Pinus, Tsuga) collected between 1960 and 2014. Temporal variability in mast seeding (CVp) for 2 year genera (Abies, Picea, Tsuga) was higher than for Pinus (3 year), and serotinous species had lower CVp than non-serotinous species; there were no relationships of CVp with elevation or latitude. There was no difference in family-wide CVp across four tree regions of North America. Across all genera, July temperature differences between bud initiation and the prior year (Δ𝑇) was more strongly associated with reproduction than absolute temperature. Both CVp and Δ𝑇 remained steady over time, while absolute temperature increased by 0.09°C per decade. Our use of the Δ𝑇 model included a modification for Pinus, which initiates cone primordia 2 years before seedfall, as opposed to 1 year. These findings have implications for how mast-seeding patterns may change with future increases in temperature, and the adaptive benefits of mast seeding.
This article is part of the theme issue 'The ecology and evolution of synchronized seed production in plants'.
Journal Article
Increasing fire and the decline of fire adapted black spruce in the boreal forest
Intensifying wildfire activity and climate change can drive rapid forest compositional shifts. In boreal North America, black spruce shapes forest flammability and depends on fire for regeneration. This relationship has helped black spruce maintain its dominance through much of the Holocene. However, with climate change and more frequent and severe fires, shifts away from black spruce dominance to broadleaf or pine species are emerging, with implications for ecosystem functions including carbon sequestration, water and energy fluxes, and wildlife habitat. Here, we predict that such reductions in black spruce after fire may already be widespread given current trends in climate and fire. To test this, we synthesize data from 1,538 field sites across boreal North America to evaluate compositional changes in tree species following 58 recent fires (1989 to 2014). While black spruce was resilient following most fires (62%), loss of resilience was common, and spruce regeneration failed completely in 18% of 1,140 black spruce sites. In contrast, postfire regeneration never failed in forests dominated by jack pine, which also possesses an aerial seed bank, or broad-leaved trees. More complete combustion of the soil organic layer, which often occurs in better-drained landscape positions and in dryer duff, promoted compositional changes throughout boreal North America. Forests in western North America, however, were more vulnerable to change due to greater long-term climate moisture deficits. While we find considerable remaining resilience in black spruce forests, predicted increases in climate moisture deficits and fire activity will erode this resilience, pushing the system toward a tipping point that has not been crossed in several thousand years.
Journal Article
Seed maturation and mortality patterns support non-serotinous conifer regeneration mechanism following high-severity fire
Background
Climate warming increases fire activity for many regions around the world, prompting concern over the long-term persistence of conifer species that regenerate poorly from seed after high-severity fire. However, substantive regeneration of non-serotinous conifer species within a large high-severity patch, a process we refer to as conditional pyriscence, is possible if the fire occurs in the window following seed maturation but before cone opening, the enclosed seeds can withstand the heat range of the fire, and the non-serotinous cone crop is sufficient. To define this temporal window, we collected closed cones from June to September over two seasons, examining seed maturation as a function of the heat sum for four non-serotinous California conifer species: ponderosa pine (
Pinus ponderosa
), Sierra lodgepole pine (
Pinus contorta
var.
murrayana
), incense cedar (
Calocedrus decurrens
), and Douglas-fir (
Pseudotsuga menziesii
). Additionally, we examined seed survival based on viability testing in closed cones following heat treatments ranging from ~ 20 to 600 °C. Finally, we overlayed the period of viability with the timing of fires for northern California to identify the proportion of fires that may be conducive to conditional pyriscence.
Results
The accumulated heat sum was positively associated with seed maturity; the proportion of seeds that were viable varied by species but generally ranged from late-July (10%) to mid-September (90%) with heat sums ranging from 1285 to 2081 °C, respectively. Higher cone heat exposure was negatively associated with seed survival and some withstood temperatures as high as 400 °C for 150 s. Seeds of the smaller cone species tended to have lower survivability to heat treatments than the larger cone species. The period of availability of mature seeds overlapped with 60% of the area burned during wildfires for northern California.
Conclusions
We identify circumstances suitable for conditional pyriscence following high-severity fires for four non-serotinous conifers in northern California. The temporal window that permits conditional pyriscence for these species may provide one explanation as to why some large high severity patches can result in substantive seedling regeneration. Inclusion of this information has potential to improve post-fire regeneration modeling and can aid forest management decision-making in fire-prone ecosystems containing non-serotinous conifers.
Journal Article