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3.
Nature ; 589(7842): 402-407, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33473224

RESUMO

Lake ecosystems, and the organisms that live within them, are vulnerable to temperature change1-5, including the increased occurrence of thermal extremes6. However, very little is known about lake heatwaves-periods of extreme warm lake surface water temperature-and how they may change under global warming. Here we use satellite observations and a numerical model to investigate changes in lake heatwaves for hundreds of lakes worldwide from 1901 to 2099. We show that lake heatwaves will become hotter and longer by the end of the twenty-first century. For the high-greenhouse-gas-emission scenario (Representative Concentration Pathway (RCP) 8.5), the average intensity of lake heatwaves, defined relative to the historical period (1970 to 1999), will increase from 3.7 ± 0.1 to 5.4 ± 0.8 degrees Celsius and their average duration will increase dramatically from 7.7 ± 0.4 to 95.5 ± 35.3 days. In the low-greenhouse-gas-emission RCP 2.6 scenario, heatwave intensity and duration will increase to 4.0 ± 0.2 degrees Celsius and 27.0 ± 7.6 days, respectively. Surface heatwaves are longer-lasting but less intense in deeper lakes (up to 60 metres deep) than in shallower lakes during both historic and future periods. As lakes warm during the twenty-first century7,8, their heatwaves will begin to extend across multiple seasons, with some lakes reaching a permanent heatwave state. Lake heatwaves are likely to exacerbate the adverse effects of long-term warming in lakes and exert widespread influence on their physical structure and chemical properties. Lake heatwaves could alter species composition by pushing aquatic species and ecosystems to the limits of their resilience. This in turn could threaten lake biodiversity9 and the key ecological and economic benefits that lakes provide to society.


Assuntos
Ecossistema , Calor Extremo , Aquecimento Global/estatística & dados numéricos , Lagos , Animais , Organismos Aquáticos , Calor Extremo/efeitos adversos , Mapeamento Geográfico , Humanos , Estações do Ano
5.
Nature ; 584(7821): 393-397, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32814886

RESUMO

The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood1. Previous assessments found that the summed contributions of ice-mass loss, terrestrial water storage and thermal expansion of the ocean could not be reconciled with observed changes in global-mean sea level, implying that changes in sea level or some contributions to those changes were poorly constrained2,3. Recent improvements to observational data, our understanding of the main contributing processes to sea-level change and methods for estimating the individual contributions, mean another attempt at reconciliation is warranted. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss-predominantly from glaciers-has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.


Assuntos
Temperatura Alta , Camada de Gelo/química , Água do Mar/análise , Água do Mar/química , Monitoramento Ambiental , Aquecimento Global/estatística & dados numéricos , Groenlândia , História do Século XX , História do Século XXI , Probabilidade , Incerteza
6.
Nature ; 584(7819): 82-86, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32760046

RESUMO

Marine heatwaves (MHWs)-discrete but prolonged periods of anomalously warm ocean temperatures-can drastically alter ocean ecosystems, with profound ecological and socioeconomic impacts1-8. Considerable effort has been directed at understanding the patterns, drivers and trends of MHWs globally9-11. Typically, MHWs are characterized on the basis of their intensity and persistence at a given location-an approach that is particularly relevant for corals and other sessile organisms that must endure increased temperatures. However, many ecologically and commercially important marine species respond to environmental disruptions by relocating to favourable habitats, and dramatic range shifts of mobile marine species are among the conspicuous impacts of MHWs1,4,12,13. Whereas spatial temperature shifts have been studied extensively in the context of long-term warming trends14-18, they are unaccounted for in existing global MHW analyses. Here we introduce thermal displacement as a metric that characterizes MHWs by the spatial shifts of surface temperature contours, instead of by local temperature anomalies, and use an observation-based global sea surface temperature dataset to calculate thermal displacements for all MHWs from 1982 to 2019. We show that thermal displacements during MHWs vary from tens to thousands of kilometres across the world's oceans and do not correlate spatially with MHW intensity. Furthermore, short-term thermal displacements during MHWs are of comparable magnitude to century-scale shifts inferred from warming trends18, although their global spatial patterns are very different. These results expand our understanding of MHWs and their potential impacts on marine species, revealing which regions are most susceptible to thermal displacement, and how such shifts may change under projected ocean warming. The findings also highlight the need for marine resource management to account for MHW-driven spatial shifts, which are of comparable scale to those associated with long-term climate change and are already happening.


Assuntos
Migração Animal , Organismos Aquáticos , Ecossistema , Calor Extremo , Aquecimento Global , Água do Mar/análise , Animais , Calor Extremo/efeitos adversos , Aquecimento Global/estatística & dados numéricos , História do Século XX , História do Século XXI , Modelos Teóricos , Oceanos e Mares
11.
Rev Med Suisse ; 16(694): 1049-1055, 2020 May 20.
Artigo em Francês | MEDLINE | ID: mdl-32432423

RESUMO

Global warming is considered by most scientists as one of the greatest public health threats of the 21st century. Some individual behaviours and consumption habits related to the food and mobility sectors are responsible for a high amount of CO2 emissions, the main greenhouse gas. Thus, some messages promoted by health professionals will have an impact on the fight against the epidemic of lifestyle-related chronic diseases but will also have an environmental co-benefit. With a population increasingly aware of current environmental issues, environmental considerations could be an additional motivating factor for patients when promoting a healthier diet or physical activity.


Assuntos
Agricultura/estatística & dados numéricos , Dieta/estatística & dados numéricos , Aquecimento Global/estatística & dados numéricos , Promoção da Saúde/estatística & dados numéricos , Saúde Pública/estatística & dados numéricos , Exercício Físico , Humanos
12.
Nature ; 581(7808): 294-298, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32433620

RESUMO

Warming surface temperatures have driven a substantial reduction in the extent and duration of Northern Hemisphere snow cover1-3. These changes in snow cover affect Earth's climate system via the surface energy budget, and influence freshwater resources across a large proportion of the Northern Hemisphere4-6. In contrast to snow extent, reliable quantitative knowledge on seasonal snow mass and its trend is lacking7-9. Here we use the new GlobSnow 3.0 dataset to show that the 1980-2018 annual maximum snow mass in the Northern Hemisphere was, on average, 3,062 ± 35 billion tonnes (gigatonnes). Our quantification is for March (the month that most closely corresponds to peak snow mass), covers non-alpine regions above 40° N and, crucially, includes a bias correction based on in-field snow observations. We compare our GlobSnow 3.0 estimates with three independent estimates of snow mass, each with and without the bias correction. Across the four datasets, the bias correction decreased the range from 2,433-3,380 gigatonnes (mean 2,867) to 2,846-3,062 gigatonnes (mean 2,938)-a reduction in uncertainty from 33% to 7.4%. On the basis of our bias-corrected GlobSnow 3.0 estimates, we find different continental trends over the 39-year satellite record. For example, snow mass decreased by 46 gigatonnes per decade across North America but had a negligible trend across Eurasia; both continents exhibit high regional variability. Our results enable a better estimation of the role of seasonal snow mass in Earth's energy, water and carbon budgets.


Assuntos
Mapeamento Geográfico , Neve , Análise Espaço-Temporal , Viés , Carbono/análise , Planeta Terra , Aquecimento Global/estatística & dados numéricos , História do Século XX , História do Século XXI , América do Norte , Estações do Ano , Sibéria , Neve/química , Temperatura , Incerteza , Água/análise
13.
Nature ; 580(7804): 496-501, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-32322063

RESUMO

As anthropogenic climate change continues the risks to biodiversity will increase over time, with future projections indicating that a potentially catastrophic loss of global biodiversity is on the horizon1-3. However, our understanding of when and how abruptly this climate-driven disruption of biodiversity will occur is limited because biodiversity forecasts typically focus on individual snapshots of the future. Here we use annual projections (from 1850 to 2100) of temperature and precipitation across the ranges of more than 30,000 marine and terrestrial species to estimate the timing of their exposure to potentially dangerous climate conditions. We project that future disruption of ecological assemblages as a result of climate change will be abrupt, because within any given ecological assemblage the exposure of most species to climate conditions beyond their realized niche limits occurs almost simultaneously. Under a high-emissions scenario (representative concentration pathway (RCP) 8.5), such abrupt exposure events begin before 2030 in tropical oceans and spread to tropical forests and higher latitudes by 2050. If global warming is kept below 2 °C, less than 2% of assemblages globally are projected to undergo abrupt exposure events of more than 20% of their constituent species; however, the risk accelerates with the magnitude of warming, threatening 15% of assemblages at 4 °C, with similar levels of risk in protected and unprotected areas. These results highlight the impending risk of sudden and severe biodiversity losses from climate change and provide a framework for predicting both when and where these events may occur.


Assuntos
Biodiversidade , Mapeamento Geográfico , Aquecimento Global/estatística & dados numéricos , Animais , Organismos Aquáticos , Florestas , História do Século XIX , História do Século XX , História do Século XXI , Chuva , Temperatura , Fatores de Tempo , Clima Tropical
17.
Nature ; 579(7799): 393-396, 2020 03.
Artigo em Inglês | MEDLINE | ID: mdl-32188954

RESUMO

Agricultural practices constitute both the greatest cause of biodiversity loss and the greatest opportunity for conservation1,2, given the shrinking scope of protected areas in many regions. Recent studies have documented the high levels of biodiversity-across many taxa and biomes-that agricultural landscapes can support over the short term1,3,4. However, little is known about the long-term effects of alternative agricultural practices on ecological communities4,5 Here we document changes in bird communities in intensive-agriculture, diversified-agriculture and natural-forest habitats in 4 regions of Costa Rica over a period of 18 years. Long-term directional shifts in bird communities were evident in intensive- and diversified-agricultural habitats, but were strongest in intensive-agricultural habitats, where the number of endemic and International Union for Conservation of Nature (IUCN) Red List species fell over time. All major guilds, including those involved in pest control, pollination and seed dispersal, were affected. Bird communities in intensive-agricultural habitats proved more susceptible to changes in climate, with hotter and drier periods associated with greater changes in community composition in these settings. These findings demonstrate that diversified agriculture can help to alleviate the long-term loss of biodiversity outside natural protected areas1.


Assuntos
Agricultura/métodos , Agricultura/estatística & dados numéricos , Biodiversidade , Aves/classificação , Florestas , Animais , Bovinos , Costa Rica , Produtos Agrícolas/provisão & distribução , Extinção Biológica , Agricultura Florestal/estatística & dados numéricos , Aquecimento Global/estatística & dados numéricos , Controle Biológico de Vetores , Polinização , Dispersão de Sementes , Fatores de Tempo
20.
Nature ; 578(7795): 409-412, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32076219

RESUMO

Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era1. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate2,3. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century4,5. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year)2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year6,7. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago8, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)-an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions9,10.


Assuntos
Atmosfera/química , Combustíveis Fósseis/história , Combustíveis Fósseis/provisão & distribução , Atividades Humanas/história , Metano/análise , Metano/história , Biomassa , Radioisótopos de Carbono , Carvão Mineral/história , Carvão Mineral/provisão & distribução , Aquecimento Global/prevenção & controle , Aquecimento Global/estatística & dados numéricos , História do Século XVIII , História do Século XIX , História do Século XX , História do Século XXI , Camada de Gelo/química , Metano/química , Gás Natural/história , Gás Natural/provisão & distribução , Petróleo/história , Petróleo/provisão & distribução
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