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Temperature variability over Africa during the last 2000 years (2013)

Nicholson, S. E., Nash, D. J., Chase, B. M., Grab, S. W., Shanahan, T. M., Verschuren, D., Asrat, A., Lezine, A.-M., Umer, M.

Sage

In: Holocene

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Publikationsdatum: 2013-07-06

Beschreibung: A growing number of proxy, historical and instrumental data sets are now available from continental Africa through which past variations in temperature can be assessed. This paper, co-authored by members of the PAGES Africa2k Working Group, synthesises published material to produce a record of temperature variability for Africa as a whole spanning the last 2000 years. The paper focuses on temperature variability during the ‘Medieval Climate Anomaly’ (MCA), ‘Little Ice Age’ (LIA) and late 19th–early 21st centuries. Warmer conditions during the MCA are evident in records from Lake Tanganyika in central Africa, the Ethiopian Highlands in northeastern Africa, and Cango Cave, the Kuiseb River and Wonderkrater in southern Africa. Other records covering the MCA give ambiguous signals. Warming appears to have been greater during the early MCA (c. ad 1000) in parts of southern Africa and during the later MCA (from ad 1100) in Namibia, Ethiopia and at Lake Tanganyika. LIA cooling is evident in Ethiopian and southern African pollen records and in organic biomarker data from Lake Malawi in southeastern tropical Africa, while at Lake Tanganyika the temperature depression appears to have been less consistent. A warming trend in mean annual temperatures is clearly evident from historical and instrumental data covering the late 19th to early 21st centuries. General warming has occurred over Africa since the 1880s punctuated only by a period of cooling in the mid 20th century. The rate of temperature increase appears to have accelerated towards the end of the 20th century. The few long high-resolution proxy records that extend into the late 20th century indicate that average annual temperatures were 1–2°C higher in the last few decades than during the MCA.

Print ISSN: 0959-6836

Digitale ISSN: 1477-0911

Thema: Geographie , Geologie und Paläontologie

Publiziert von Sage

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Past and future global transformation of terrestrial ecosystems under climate change (2018)

Nolan, C., Overpeck, J. T., Allen, J. R. M., Anderson, P. M., Betancourt, J. L., Binney, H. A., Brewer, S., Bush, M. B., Chase, B. M., Cheddadi, R., Djamali, M., Dodson, J., Edwards, M. E., Gosling, W. D., Haberle, S., Hotchkiss, S. C., Huntley, B., Ivory, S. J., Kershaw, A. P., Kim, S.-H., Latorre, C., Leydet, M., Lezine, A.-M., Liu, K.-B., Liu, Y., Lozhkin, A. V., McGlone, M. S., Marchant, R. A., Momohara, A., Moreno, P. I., Müller, S., Otto-Bliesner, B. L., Shen, C., Stevenson, J., Takahara, H., Tarasov, P. E., Tipton, J., Vincens, A., Weng, C., Xu, Q., Zheng, Z., Jackson, S. T.

American Association for the Advancement of Science (AAAS)

In: Science

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Publikationsdatum: 2018-08-31

Beschreibung: Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

Schlagwort(e): Atmospheric Science, Ecology

Print ISSN: 0036-8075

Digitale ISSN: 1095-9203

Thema: Biologie , Chemie und Pharmazie , Geologie und Paläontologie , Informatik , Medizin , Allgemeine Naturwissenschaft , Physik

Publiziert von American Association for the Advancement of Science (AAAS)

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Precipitation variability in the winter rainfall zone of South Africa during the last 1400 yr linked to the austral westerlies (2011)

Stager, J. C. ; Mayewski, P. A. ; White, J. ; [weitere]

Copernicus

In: Climate of the Past Discussions. 2011; 7(6): 4375-4399. Published 2011 Dec 20. doi: 10.5194/cpd-7-4375-2011.

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Publikationsdatum: 2011-12-20

Beschreibung: The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward contraction of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been largely limited to South America, are not fully consistent with each other, and may be complicated by influences from other climatic factors. Here we present the first fine-interval diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation during the last 1400 yr. Inferred rainfall increased ~1400–1200 cal yr BP and most notably during the Little Ice Age with pulses centered on ~600, 530, 470, 330, 200, and 90 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations are linked to changes in the westerlies. Partial inconsistencies among South African and South American records warn against the simplistic application of local-scale histories to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in austral winter rainfall zones with future warming.

Print ISSN: 1814-9340

Digitale ISSN: 1814-9359

Thema: Geologie und Paläontologie

Publiziert von Copernicus im Namen von European Geosciences Union.

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CREST: Climate REconstruction SofTware (2014)

Chevalier, M. ; Cheddadi, R. ; Chase, B. M.

Copernicus

In: Climate of the Past Discussions. 2014; 10(1): 625-663. Published 2014 Feb 17. doi: 10.5194/cpd-10-625-2014.

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Publikationsdatum: 2014-02-17

Beschreibung: Several methods currently exist to quantitatively reconstruct palaeoclimatic variables from fossil botanical data. Of these, pdf-based (probability density functions) methods have proven valuable as they can be applied to a wide range of plants assemblages. Most commonly applied to fossil pollen data, their performance, however, can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen-type. Consequently, the climate information associated with different species cannot sometimes not be precisely identified, resulting less accurate reconstructions. This can become particularly problematic in regions of high biodiversity. In this paper, we propose a novel pdf-based method that takes into account the different climatic requirements of each species constituting the broader pollen-type. Pdfs are fitted in two successive steps, with parametric pdfs fitted first for each species, and then a combination of those individual species pdfs into a broader single pdf to represent the pollen-type as a unit. A climate value for the pollen assemblage is estimated from the likelihood function obtained after the multiplication of the pollen-type pdfs, with each being weighted according to its pollen percentage. To test the robustness of the method, we have applied the method to southern Africa as a regional case study, and reconstructed a suite of climatic variables based on extensive botanical data derived from herbarium collections. The reconstructions proved to be accurate for both temperature and precipitation. Predictable exceptions were areas that experience conditions at the extremes of the regional climatic spectra. Importantly, the accuracy of the reconstructed values is independent from the vegetation type where the method is applied or the number of species used. The method used in this study is publicly available in a software package entitled CREST (Climate REconstruction SofTware) and will provide the opportunity to reconstruct reliable quantitative estimates of climatic variables even in areas with high geographical and botanical diversity.

Print ISSN: 1814-9340

Digitale ISSN: 1814-9359

Thema: Geologie und Paläontologie

Publiziert von Copernicus im Namen von European Geosciences Union.

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Precipitation variability in the winter rainfall zone of South Africa during the last 1400 yr linked to the austral westerlies (2012)

Stager, J. C. ; Mayewski, P. A. ; White, J. ; [weitere]

Copernicus

In: Climate of the Past. 2012; 8(3): 877-887. Published 2012 May 03. doi: 10.5194/cp-8-877-2012.

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Publikationsdatum: 2012-05-03

Beschreibung: The austral westerlies strongly influence precipitation and ocean circulation in the southern temperate zone, with important consequences for cultures and ecosystems. Global climate models anticipate poleward retreat of the austral westerlies with future warming, but the available paleoclimate records that might test these models have been limited to South America and New Zealand, are not fully consistent with each other and may be complicated by influences from other climatic factors. Here we present the first high-resolution diatom and sedimentological records from the winter rainfall region of South Africa, representing precipitation in the equatorward margin of the westerly wind belt during the last 1400 yr. Inferred rainfall was relatively high ∼1400–1200 cal yr BP, decreased until ∼950 cal yr BP, and rose notably through the Little Ice Age with pulses centred on ∼600, 530, 470, 330, 200, 90, and 20 cal yr BP. Synchronous fluctuations in Antarctic ice core chemistry strongly suggest that these variations were linked to changes in the westerlies. Equatorward drift of the westerlies during the wet periods may have influenced Atlantic meridional overturning circulation by restricting marine flow around the tip of Africa. Apparent inconsistencies among some aspects of records from South America, New Zealand and South Africa warn against the simplistic application of single records to the Southern Hemisphere as a whole. Nonetheless, these findings in general do support model projections of increasing aridity in the austral winter rainfall zones with future warming.

Print ISSN: 1814-9324

Digitale ISSN: 1814-9332

Thema: Geologie und Paläontologie

Publiziert von Copernicus im Namen von European Geosciences Union.

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CREST (Climate REconstruction SofTware): a probability density function (PDF)-based quantitative climate reconstruction method (2014)

Chevalier, M. ; Cheddadi, R. ; Chase, B. M.

Copernicus

In: Climate of the Past. 2014; 10(6): 2081-2098. Published 2014 Nov 28. doi: 10.5194/cp-10-2081-2014.

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Publikationsdatum: 2014-11-28

Beschreibung: Several methods currently exist to quantitatively reconstruct palaeoclimatic variables from fossil botanical data. Of these, probability density function (PDF)-based methods have proven valuable as they can be applied to a wide range of plant assemblages. Most commonly applied to fossil pollen data, their performance, however, can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen type. Consequently, the climate information associated with different species cannot always be precisely identified, resulting in less-accurate reconstructions. This can become particularly problematic in regions of high biodiversity. In this paper, we propose a novel PDF-based method that takes into account the different climatic requirements of each species constituting the broader pollen type. PDFs are fitted in two successive steps, with parametric PDFs fitted first for each species and then a combination of those individual species PDFs into a broader single PDF to represent the pollen type as a unit. A climate value for the pollen assemblage is estimated from the likelihood function obtained after the multiplication of the pollen-type PDFs, with each being weighted according to its pollen percentage. To test its performance, we have applied the method to southern Africa as a regional case study and reconstructed a suite of climatic variables (e.g. winter and summer temperature and precipitation, mean annual aridity, rainfall seasonality). The reconstructions are shown to be accurate for both temperature and precipitation. Predictable exceptions were areas that experience conditions at the extremes of the regional climatic spectra. Importantly, the accuracy of the reconstructed values is independent of the vegetation type where the method is applied or the number of species used. The method used in this study is publicly available in a software package entitled CREST (Climate REconstruction SofTware) and will provide the opportunity to reconstruct quantitative estimates of climatic variables even in areas with high geographical and botanical diversity.

Print ISSN: 1814-9324

Digitale ISSN: 1814-9332

Thema: Geologie und Paläontologie

Publiziert von Copernicus im Namen von European Geosciences Union.

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