scholarly journals Global acceleration in rates of vegetation change over the past 18,000 years

Science ◽  
2021 ◽  
Vol 372 (6544) ◽  
pp. 860-864
Author(s):  
Ondřej Mottl ◽  
Suzette G. A. Flantua ◽  
Kuber P. Bhatta ◽  
Vivian A. Felde ◽  
Thomas Giesecke ◽  
...  
Keyword(s):  
Vegetation Change ◽  
Terrestrial Ecosystems ◽  
Past Century ◽  
Last Deglaciation ◽  
The Past ◽  
Rates Of Change ◽  
Biodiversity Change ◽  
Human Effects ◽  
The Last Deglaciation ◽  
Global Vegetation

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago.

scholarly journals Improved estimates of preindustrial biomass burning reduce the magnitude of aerosol climate forcing in the Southern Hemisphere

2021 ◽  
Vol 7 (22) ◽  
pp. eabc1379
Author(s):  
Pengfei Liu ◽  
Jed O. Kaplan ◽  
Loretta J. Mickley ◽  
Yang Li ◽  
Nathan J. Chellman ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Radiative Forcing ◽  
Ice Core ◽  
Ice Cores ◽  
Terrestrial Ecosystems ◽  
Rapid Expansion ◽  
Past Century ◽  
Fire Emissions ◽  
The Past ◽  
Fire Activity

Fire plays a pivotal role in shaping terrestrial ecosystems and the chemical composition of the atmosphere and thus influences Earth’s climate. The trend and magnitude of fire activity over the past few centuries are controversial, which hinders understanding of preindustrial to present-day aerosol radiative forcing. Here, we present evidence from records of 14 Antarctic ice cores and 1 central Andean ice core, suggesting that historical fire activity in the Southern Hemisphere (SH) exceeded present-day levels. To understand this observation, we use a global fire model to show that overall SH fire emissions could have declined by 30% over the 20th century, possibly because of the rapid expansion of land use for agriculture and animal production in middle to high latitudes. Radiative forcing calculations suggest that the decreasing trend in SH fire emissions over the past century largely compensates for the cooling effect of increasing aerosols from fossil fuel and biofuel sources.

scholarly journals The Meridional Shift of the Midlatitude Westerlies over Arid Central Asia during the Past 21 000 Years Based on the TraCE-21ka Simulations

2020 ◽  
Vol 33 (17) ◽  
pp. 7455-7478
Author(s):  
Nanxuan Jiang ◽  
Qing Yan ◽  
Zhiqing Xu ◽  
Jian Shi ◽  
Ran Zhang
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Last Deglaciation ◽  
The Past ◽  
The North ◽  
External Forcings ◽  
The Indian Ocean ◽  
The Last Deglaciation ◽  
The North Atlantic

AbstractTo advance our knowledge of the response of midlatitude westerlies to various external forcings, we investigate the meridional shift of midlatitude westerlies over arid central Asia (ACA) during the past 21 000 years, which experienced more varied forcings than the present day based on a set of transient simulations. Our results suggest that the evolution of midlatitude westerlies over ACA and driving factors vary with time and across seasons. In spring, the location of midlatitude westerlies over ACA oscillates largely during the last deglaciation, driven by meltwater fluxes and continental ice sheets, and then shows a long-term equatorward shift during the Holocene controlled by orbital insolation. In summer, orbital insolation dominates the meridional shift of midlatitude westerlies, with poleward and equatorward migration during the last deglaciation and the Holocene, respectively. From a thermodynamic perspective, variations in zonal winds are linked with the meridional temperature gradient based on the thermal wind relationship. From a dynamic perspective, variations in midlatitude westerlies are mainly induced by anomalous sea surface temperatures over the Indian Ocean through the Matsuno–Gill response and over the North Atlantic Ocean by the propagation of Rossby waves, or both, but their relative importance varies across forcings. Additionally, the modeled meridional shift of midlatitude westerlies is broadly consistent with geological evidence, although model–data discrepancies still exist. Overall, our study provides a possible scenario for a meridional shift of midlatitude westerlies over ACA in response to various external forcings during the past 21 000 years and highlights important roles of both the Indian Ocean and the North Atlantic Ocean in regulating Asian westerlies, which may shed light on the behavior of westerlies in the future.

scholarly journals The Mysterious 14C Decline

Radiocarbon ◽  
2009 ◽  
Vol 51 (1) ◽  
pp. 109-119 ◽  
Author(s):  
Wallace Broecker
Keyword(s):  
Age Differences ◽  
Radiocarbon Dating ◽  
Progressive Increase ◽  
Time Interval ◽  
Last Deglaciation ◽  
Polar Ice ◽  
Radiocarbon Age ◽  
Surface Ocean ◽  
The Past ◽  
The Last Deglaciation

Fundamental to the field of radiocarbon dating is not only the establishment of the temporal record of the calendar age-radiocarbon age offsets but also the development of an understanding of their cause. Although part of the decline in the magnitude of this offset over the past 40,000 can be explained by a drop in 14C production rate associated with a progressive increase in the strength of the Earth's magnetic shielding, it is clear that changes in the distribution of 14C among the Earth's active carbon reservoirs are also required. In particular, the steep 15% decline in the 14C to C ratio in atmospheric CO2 and surface ocean ΣCO2, which occurred in a 3 kyr-duration interval marking the onset of the last deglaciation, appears to require that a very large amount (at least 5000 gigatons) of 14C-deficient carbon was transferred to or within the ocean during this time interval. As no chemical or stable isotope anomaly associated with this injection appears in either the marine sediment or polar ice records, this injection must involve a transfer within the ocean (i.e. a mixing of 2 ocean reservoirs, one depleted in 14C and the other enriched in 14C). Although evidence for the existence of a salt-stabilized glacial-age abyssal ocean reservoir exists, a search based on benthic-planktic age differences and 13C measurements appears to place a limit on its size well below that required to account for the steep 14C decline.

scholarly journals Vegetation change and the protection of the Csaroda relic mires, Hungary

2014 ◽  
Vol 61 (1) ◽  
pp. 63-74 ◽  
Author(s):  
Tibor Simon
Keyword(s):  
Vegetation Change ◽  
Climatic Variation ◽  
Forest Growth ◽  
Slight Effect ◽  
Raised Bog ◽  
Qualitative And Quantitative ◽  
The Past ◽  
Drainage Canals ◽  
Human Effects ◽  
Hungarian Plain

Study of vegetation change of the protected mires situated near Csaroda and Beregdaróc (the Great Hungarian Plain) are presented. These are the southermost mires with raised bog communities in the plains of Europe. In the past few decades (by the early 80-s) vegetation showed both qualitative and quantitative signs of degradation. These changes were caused by natural (climatic variation, succesion) and by human effects. Natural changes were following: the decline or extinction of hygrophytes, the expansion of hydromesophytes and mesophytes and the acceleration of forest growth. The most important human-caused change was the drainage of the bogs. The harmful processes had slight effect on the <i>Sphagnum</i>-dominated associations. The "original" (i.e. before drying out) state of mires has been recovered by blocking drainage canals, plantation of a buffor zone and prohibition of using chemicals.

Climate and abrupt vegetation change in Northern Europe since the last deglaciation

The Holocene ◽  
2014 ◽  
Vol 25 (1) ◽  
pp. 25-36 ◽  
Author(s):  
Alistair WR Seddon ◽  
Marc Macias-Fauria ◽  
Kathy J Willis
Keyword(s):  
Vegetation Change ◽  
Northern Europe ◽  
Last Deglaciation ◽  
The Last Deglaciation

Centennial-scale evolution of methane during the penultimate deglaciation

2020 ◽  
Author(s):  
Loïc Schmidely ◽  
Lucas Silva ◽  
Christoph Nehrbass-Ahles ◽  
Juhyeong Han ◽  
Jinhwa Shin ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Ice Core ◽  
Ice Cores ◽  
Before Present ◽  
Last Deglaciation ◽  
Rates Of Change ◽  
Maximum Resolution ◽  
The Last Deglaciation ◽  
First Time ◽  
Temporal Coverage

&lt;p&gt; Small air inclusions in ice cores represent a direct archive of past atmospheric compositions, allowing us to measure the concentration of the three most potent non-condensable Greenhouse Gases (GHG) CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O as far back as 800,000 years before present (kyr BP). These records demonstrate that transitions from glacial to interglacial conditions are accompanied by a substantial net increase of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O in the atmosphere (L&amp;#252;thi et al. 2008, Loulergue et al. 2008, Schilt et al. 2010). A sound understanding of the interplay between the reorganization of the climate system and the perturbation of GHG inventories during glacial terminations is partly limited by the temporal resolution of the records derived from ice cores. In fact, with the exception of the last deglaciation (23-9 kyr BP) centennial-scale GHG variability remained uncaptured for precedings glacial terminations.&lt;/p&gt;&lt;p&gt;In this work, we exploit the exceptionally long temporal coverage of the EPICA Dome C (EDC) ice core to reconstruct, for the first time, centennial-scale fluctuations of CH&lt;sub&gt;4&lt;/sub&gt; mole fractions from 145 to 125 kyr BP, encompassing the entire penultimate deglaciation (138-128 kyr BP). With a temporal resolution of ~100 years, our new record is now unveiling all climate-driven signals enclosed into the EDC ice core, exploiting the maximum resolution possible at Dome C (). This offers us the opportunity to study the timing and rates of change of CH&lt;sub&gt;4&lt;/sub&gt; in unprecedented details.&lt;/p&gt;&lt;p&gt;Preliminary analysis reveals that the deglacial CH&lt;sub&gt;4 &lt;/sub&gt;rise is a superimposition of gradual millennial-scale increases (~0.01-0.02 ppb/year) and abrupt and partly intermittent centennial-scale events (~80-200 ppb in less than a millennium). We will investigate processes modulating the observed changes in the CH&lt;sub&gt;4&lt;/sub&gt; cycle, compare the structure of our record with the CH&lt;sub&gt;4&lt;/sub&gt; profile of the last deglaciation (Marcott, 2014) and contrast it with the EDC CO&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O records over the penultimate glacial termination now available in similar resolution.&lt;/p&gt;

scholarly journals Causes and timing of recurring subarctic Pacific hypoxia

2021 ◽  
Vol 7 (23) ◽  
pp. eabg2906
Author(s):  
Karla P. Knudson ◽  
Ana Christina Ravelo ◽  
Ivano W. Aiello ◽  
Christina P. Knudson ◽  
Michelle K. Drake ◽  
...  
Keyword(s):  
Laminated Sediments ◽  
Last Deglaciation ◽  
Glacial Cycles ◽  
Sea Levels ◽  
Subarctic Pacific ◽  
High Productivity ◽  
The Past ◽  
Continental Shelves ◽  
Pacific Studies ◽  
The Last Deglaciation

Several North Pacific studies of the last deglaciation show hypoxia throughout the ocean margins and attribute this phenomenon to the effects of abrupt warming and meltwater inputs. Yet, because of the lack of long records spanning multiple glacial cycles and deglaciation events, it is unclear whether deoxygenation was a regular occurrence of warming events and whether deglaciation and/or other conditions promoted hypoxia throughout time. Here, subarctic Pacific laminated sediments from the past 1.2 million years demonstrate that hypoxic events recurred throughout the Pleistocene as episodes of highly productive phytoplankton growth and were generally associated with interglacial climates, high sea levels, and enhanced nitrate utilization—but not with deglaciations. We suggest that hypoxia was typically stimulated by high productivity from iron fertilization facilitated by redox-remobilized iron from flooded continental shelves.

scholarly journals CH<sub>4</sub> and N<sub>2</sub>O fluctuations during the penultimate deglaciation

2021 ◽  
Vol 17 (4) ◽  
pp. 1627-1643
Author(s):  
Loïc Schmidely ◽  
Christoph Nehrbass-Ahles ◽  
Jochen Schmitt ◽  
Juhyeong Han ◽  
Lucas Silva ◽  
...  
Keyword(s):  
Ice Core ◽  
Last Deglaciation ◽  
Glacial Cycle ◽  
Last Glacial Period ◽  
Modes Of Variability ◽  
The Past ◽  
Present Composite ◽  
The Last Deglaciation ◽  
Ch4 And N2o ◽  
The Last Glacial

Abstract. Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 000 years. Reconstructions of millennial- to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of ∼100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At ∼134 000 and ∼129 000 years before present (hereafter ka), both CH4 and N2O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard–Oeschger events identified in the last glacial period. In addition, gradually rising N2O levels at ∼130 ka resemble a pattern of increasing N2O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH4 and N2O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed.

Our Environmental Future

2017 ◽  
Author(s):  
Morton Lippmann ◽  
Richard B. Schlesinger
Keyword(s):  
Adverse Effects ◽  
Human Health ◽  
Rapid Growth ◽  
Terrestrial Ecosystems ◽  
Pollutant Emissions ◽  
Standard Of Living ◽  
Past Century ◽  
Human Populations ◽  
The Past ◽  
Chemical Pollutant

This chapter describes the rapid growth in human populations, standard of living, chemical pollutant emissions, and ability to protect human health and welfare, while dealing with the growing stresses on aquatic and terrestrial ecosystems during the past century. It also discusses the need to, and means of anticipating the drivers of resource cosumption and usage, the and practical means that can be applied to harness our emerging technological capabilities in order to limit future chemical emissions and their capacity to cause adverse effects on human health and welfare.

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