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  • American Association for the Advancement of Science (AAAS)  (10)
  • 1
    Online Resource
    Online Resource
    Abrupt Shifts in Horn of Africa Hydroclimate Since the Last Glacial Maximum
    American Association for the Advancement of Science (AAAS) ; 2013
    In:  Science Vol. 342, No. 6160 ( 2013-11-15), p. 843-846
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 342, No. 6160 ( 2013-11-15), p. 843-846
    Abstract: The timing and abruptness of the initiation and termination of the Early Holocene African Humid Period are subjects of ongoing debate, with direct consequences for our understanding of abrupt climate change, paleoenvironments, and early human cultural development. Here, we provide proxy evidence from the Horn of Africa region that documents abrupt transitions into and out of the African Humid Period in northeast Africa. Similar and generally synchronous abrupt transitions at other East African sites suggest that rapid shifts in hydroclimate are a regionally coherent feature. Our analysis suggests that the termination of the African Humid Period in the Horn of Africa occurred within centuries, underscoring the nonlinearity of the region’s hydroclimate.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1240411
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2013
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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  • 2
    Online Resource
    Online Resource
    Northern Hemisphere vegetation change drives a Holocene thermal maximum
    American Association for the Advancement of Science (AAAS) ; 2022
    In:  Science Advances Vol. 8, No. 15 ( 2022-04-15)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 8, No. 15 ( 2022-04-15)
    Abstract: Northern Hemisphere vegetation change is critical for the reconstruction of Holocene surface temperatures.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.abj6535
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2022
    detail.hit.zdb_id: 2810933-8
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  • 3
    Online Resource
    Online Resource
    Simulation of Eocene extreme warmth and high climate sensitivity through cloud feedbacks
    American Association for the Advancement of Science (AAAS) ; 2019
    In:  Science Advances Vol. 5, No. 9 ( 2019-09-06)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 5, No. 9 ( 2019-09-06)
    Abstract: The Early Eocene, a period of elevated atmospheric CO 2 ( 〉 1000 ppmv), is considered an analog for future climate. Previous modeling attempts have been unable to reproduce major features of Eocene climate indicated by proxy data without substantial modification to the model physics. Here, we present simulations using a state-of-the-art climate model forced by proxy-estimated CO 2 levels that capture the extreme surface warmth and reduced latitudinal temperature gradient of the Early Eocene and the warming of the Paleocene-Eocene Thermal Maximum. Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C). This higher climate sensitivity is mainly attributable to the shortwave cloud feedback, which is linked primarily to cloud microphysical processes. Our findings highlight the role of small-scale cloud processes in determining large-scale climate changes and suggest a potential increase in climate sensitivity with future warming.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.aax1874
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2019
    detail.hit.zdb_id: 2810933-8
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  • 4
    Online Resource
    Online Resource
    Rainfall regimes of the Green Sahara
    American Association for the Advancement of Science (AAAS) ; 2017
    In:  Science Advances Vol. 3, No. 1 ( 2017-01-06)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 3, No. 1 ( 2017-01-06)
    Abstract: During the “Green Sahara” period (11,000 to 5000 years before the present), the Sahara desert received high amounts of rainfall, supporting diverse vegetation, permanent lakes, and human populations. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. We present a quantitative reconstruction of western Saharan precipitation derived from leaf wax isotopes in marine sediments. Our data indicate that the Green Sahara extended to 31°N and likely ended abruptly. We find evidence for a prolonged “pause” in Green Sahara conditions 8000 years ago, coincident with a temporary abandonment of occupational sites by Neolithic humans. The rainfall rates inferred from our data are best explained by strong vegetation and dust feedbacks; without these mechanisms, climate models systematically fail to reproduce the Green Sahara. This study suggests that accurate simulations of future climate change in the Sahara and Sahel will require improvements in our ability to simulate vegetation and dust feedbacks.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.1601503
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2017
    detail.hit.zdb_id: 2810933-8
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  • 5
    Online Resource
    Online Resource
    Glacial changes in tropical climate amplified by the Indian Ocean
    American Association for the Advancement of Science (AAAS) ; 2018
    In:  Science Advances Vol. 4, No. 12 ( 2018-12-07)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 4, No. 12 ( 2018-12-07)
    Abstract: The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation—a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula—a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.aat9658
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2018
    detail.hit.zdb_id: 2810933-8
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  • 6
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    Online Resource
    Northern Hemisphere Controls on Tropical Southeast African Climate During the Past 60,000 Years
    American Association for the Advancement of Science (AAAS) ; 2008
    In:  Science Vol. 322, No. 5899 ( 2008-10-10), p. 252-255
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 322, No. 5899 ( 2008-10-10), p. 252-255
    Abstract: The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (δD) and the TEX 86 (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase ∼3000 years before atmospheric carbon dioxide concentrations. δD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1160485
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2008
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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  • 7
    Online Resource
    Online Resource
    Past climates inform our future
    American Association for the Advancement of Science (AAAS) ; 2020
    In:  Science Vol. 370, No. 6517 ( 2020-11-06)
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 370, No. 6517 ( 2020-11-06)
    Abstract: As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change. Here, we review the relevancy of paleoclimate information for climate prediction and discuss the prospects for emerging methodologies to further insights gained from past climates. Advances in proxy methods and interpretations pave the way for the use of past climates for model evaluation—a practice that we argue should be widely adopted.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.aay3701
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2020
    detail.hit.zdb_id: 128410-1
    detail.hit.zdb_id: 2066996-3
    detail.hit.zdb_id: 2060783-0
    SSG: 11
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  • 8
    Online Resource
    Online Resource
    Past and future rainfall in the Horn of Africa
    American Association for the Advancement of Science (AAAS) ; 2015
    In:  Science Advances Vol. 1, No. 9 ( 2015-10-02)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 1, No. 9 ( 2015-10-02)
    Abstract: The recent decline in Horn of Africa rainfall during the March–May “long rains” season has fomented drought and famine, threatening food security in an already vulnerable region. Some attribute this decline to anthropogenic forcing, whereas others maintain that it is a feature of internal climate variability. We show that the rate of drying in the Horn of Africa during the 20th century is unusual in the context of the last 2000 years, is synchronous with recent global and regional warming, and therefore may have an anthropogenic component. In contrast to 20th century drying, climate models predict that the Horn of Africa will become wetter as global temperatures rise. The projected increase in rainfall mainly occurs during the September–November “short rains” season, in response to large-scale weakening of the Walker circulation. Most of the models overestimate short rains precipitation while underestimating long rains precipitation, causing the Walker circulation response to unrealistically dominate the annual mean. Our results highlight the need for accurate simulation of the seasonal cycle and an improved understanding of the dynamics of the long rains season to predict future rainfall in the Horn of Africa.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.1500682
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2015
    detail.hit.zdb_id: 2810933-8
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  • 9
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    Online Resource
    Emergence of an equatorial mode of climate variability in the Indian Ocean
    American Association for the Advancement of Science (AAAS) ; 2020
    In:  Science Advances Vol. 6, No. 19 ( 2020-05-08)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 6, No. 19 ( 2020-05-08)
    Abstract: Presently, the Indian Ocean (IO) resides in a climate state that prevents strong year-to-year climate variations. This may change under greenhouse warming, but the mechanisms remain uncertain, thus limiting our ability to predict future changes in climate extremes. Using climate model simulations, we uncover the emergence of a mode of climate variability capable of generating unprecedented sea surface temperature and rainfall fluctuations across the IO. This mode, which is inhibited under present-day conditions, becomes active in climate states with a shallow thermocline and vigorous upwelling, consistent with the predictions of continued greenhouse warming. These predictions are supported by modeling and proxy evidence of an active mode during glacial intervals that favored such a state. Because of its impact on hydrological variability, the emergence of such a mode would become a first-order source of climate-related risks for the densely populated IO rim.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.aay7684
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2020
    detail.hit.zdb_id: 2810933-8
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  • 10
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    Online Resource
    Climate system asymmetries drive eccentricity pacing of hydroclimate during the early Eocene greenhouse
    American Association for the Advancement of Science (AAAS) ; 2023
    In:  Science Advances Vol. 9, No. 31 ( 2023-08-04)
    Details
    In: Science Advances, American Association for the Advancement of Science (AAAS), Vol. 9, No. 31 ( 2023-08-04)
    Abstract: Paleohydrologic proxy data and climate models show how and why eccentricity and precession influenced early Eocene hydroclimate.
    Type of Medium: Online Resource
    ISSN: 2375-2548
    URL: Article
    DOI: 10.1126/sciadv.adg8022
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2023
    detail.hit.zdb_id: 2810933-8
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