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Pollen records from African highlands are scarce; hence, the paleoecology of the Afromontane forest and its responses to glacial cycles are poorly known. Lake Bambili (Cameroon) provides a record of vegetation changes in the tropical mountains of Africa over the past 90,000 years, with high temporal resolution. Pollen data and biome reconstructions show a diverging response of forests to climate changes; the upper tree line was extremely unstable, shifting substantially in response to glacial-interglacial climate alternation, whereas the transition between the montane and lowland forests remained remarkably stable. Such ecological instability may have had a critical influence on species richness in the Afromontane forests.

Available archives of past environments and climates in Senegal are relatively limited in number and concentrated in “Niayes” coastal area. The review of available data for the 6 ka–2 ka period presented here provides a major contribution, revealing that the end of AHP occurred in two successive stages. A first dry event was dated at 4.5 ka. However, its impact was considerably attenuated in this region due to specific conditions on the Atlantic coast, compared to other areas of the Sahel. Depending on the site, gallery forests were either minimally affected or, conversely, replaced by wooded grasslands. After a brief return to humid conditions, the Niayes region experienced dessication at 2.5 ka, with the drying up of water bodies and dramatic disruption of the gallery forests.

Afromontane forests host a unique biodiversity distributed in isolated high elevation habitats within a matrix of rain forests or savannahs, yet they share a remarkable flora that raises questions about past connectivity between currently isolated forests. Here, we focused on the Podocarpus latifolius - P. milanjianus complex (Podocarpaceae), the most widely distributed conifers throughout sub-Saharan African highlands, to infer its demographic history from genetic data. We sequenced the whole plastid genome, mitochondrial DNA regions, and nuclear ribosomal DNA of 88 samples from Cameroon to Angola in western Central Africa and from Kenya to the Cape region in eastern and southern Africa to reconstruct time-calibrated phylogenies and perform demographic inferences. We show that P. latifolius and P. milanjianus form a single species, whose lineages diverged during the Pleistocene, mostly between c. 200 and 300 kyrs BP, after which they underwent a wide range expansion leading to their current distributions. Confronting phylogenomic and palaeoecological data, we argue that the species originated in East Africa and reached the highlands of the Atlantic side of Africa through two probable latitudinal migration corridors: a northern one towards the Cameroon volcanic line, and a southern one towards Angola. Although the species is now rare in large parts of its range, no demographic decline was detected, probably because it occurred too recently to have left a genetic signature in our DNA sequences. Despite the ancient and highly fluctuating history of podocarps in Africa revealed by palaeobotanical records, the extended distribution of current P. latifolius/milanjianus lineages is shown to result from a more recent history, mostly during the mid-late Pleistocene, when Afromontane forests were once far more widespread and continuous.

Temperature change over the past 2,000 years has shown pronounced regional variability. An assessment of all available continental temperature reconstructions shows a clear twentieth century warming trend, but no evidence of a coherent Little Ice Age or Medieval Warm Period. Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

MIS 3 environmental conditions in Africa north of the Equator and the Arabian Peninsula have long been controversial due to data scarcity and methodological caveats. In this paper we compare 245 continental hydrological records and 11 long and continuous continental and marine cores with results from the IPSL general circulation model to discuss hydrological changes between 59 and 29 ka in North Tropical Africa, North (Mediterranean) Africa and the Arabian Peninsula. Despite a generally glacial context, wet conditions widely expanded giving place to numerous lakes, rivers and wetlands. The major result of our study is to show that humid conditions appeared much earlier and were more prevalent in the Arabian Peninsula than in Africa, due to the conjunction of monsoon rains in summer and Mediterranean rains in winter. The mechanisms driving MIS 3 humidity in our study area involve global cooling factors such as greenhouse concentrations and ice volume, which have impacted available moisture, orbital forcing, which impacts monsoon circulation and amplitude and sensitivity to the state of the Atlantic Meridional Overturning Circulation (AMOC).

Here we present hydrological and vegetation paleo-data extracted from 28 sites in West Africa from 5∘ S to 19∘ N and the past1000/PMIP4 IPSL-CM6A-LR climate model simulations covering the 850–1850 CE period to document the environmental and climatic changes that occurred during the Little Ice Age (LIA). The comparison between paleo-data and model simulations shows a clear contrast between the area spanning the Sahel and the savannah in the north, characterized by widespread drought, and the equatorial sites in the south, where humid conditions prevailed. Particular attention was paid to the Sahel, whose climatic evolution was characterized by a progressive drying trend between 1250 and 1850 CE. Three major features are highlighted: (1) the detection of two early warning signals around 1170 and 1240 CE preceding the onset of the LIA drying trend; (2) a tipping point at 1800–1850 CE characterized by a rainfall drop and an environmental degradation in the Sahel; and (3) a succession of drying events punctuating the LIA, the major one of which was dated to around 1600 CE. The climatic long-term evolution of the Sahel is associated with a gradual southward displacement of the Inter-Tropical Convergence Zone induced by the radiative cooling impacts of major volcanic eruptions that have punctuated the last millennium.

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.

Aim: Our aims were to provide a detailed chronology of past vegetation changes in the tropical mountains of west-central Africa since the Last Glacial Maximum and to discuss montane forest responses to climate change in terms of distribution and biodiversity. Location: Lake Bambili, western Cameroon (05°56′ N, 10°14′ E, 2273 m a.s.l.). Methods: Fossil pollen was extracted from a long, continuous and well-dated sedimentary sequence extending back 20,000 years. Pollen diversity and evenness estimates were based on rarefaction analysis and on Simpson's (1/D) index. Results: Forest was nearly absent from high elevations during the last glacial period. It expanded gradually from 18.4 cal. kyr BP, interrupted only by reversals coincident with the Heinrich 1 (H1) and Younger Dryas (YD) climatic events, and then suddenly collapsed at 3.3 cal. kyr BP. This switch from forest to grassland communities occurred within a time span of three centuries. After 3.3 cal. kyr BP only short and taxon-poor forest phases are recorded, specifically between 2.7 and 1 cal. kyr BP and in recent centuries. Main conclusions: Our data indicate that the mountain forests of Cameroon are recent, resulting from plant migrations from various sources from 18.4 cal. kyr BP onwards. Their progressive development closely followed intensification of the Atlantic monsoon, leading to the formation of a dense forest between 11.7 and 3.3 cal. kyr BP. The composition of this forest included the co-occurrence of species whose ranges do not overlap today, and indicates the potential for the development of unique iterations of climax forests through time. These forests appear to be very sensitive to Northern Hemisphere climate change, with phases of expansion/contraction coeval with the boreal deglacial signal, including widely recognized events such as H1, the YD and the 8.2 ka event. From 8.2 cal. kyr BP onwards, the progressive opening of the canopy is likely to reflect increased seasonality in rainfall related to more frequent El Niño/Southern Oscillation (ENSO) events. The final step of this history was the collapse of the montane forest at 3.3 cal. kyr BP. During the last millennium, very severe disruptions have meant that only the most rapidly dispersing species could spread, contributing to a drastic loss of forest biodiversity that has been accentuated by human impact in the last few centuries.

The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex, Myrsine, Symplocos , and Weinmannia , and cool-adapted plants in the families Myrtaceae, Ericaceae, and Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were used to represent past and modern habitat suitability for Podocarpus and Araucaria . The data reveals two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by a less seasonal rainfall regime from the subtropics to the equatorial region.

Postglacial expansion of deciduous oak woodlands of the Zagros—Anti-Taurus Mountains, a major biome of the Near East, was delayed until the middle Holocene at ~6300 cal. yr BP. The current hypotheses explain this delay as a consequence of a regional aridity during the early Holocene, slow migration rates of forest trees, and/or a long history of land use and agro-pastoralism in this region. In the present paper, support is given to a hypothesis that suggests different precipitation seasonalities during the early Holocene compared with the late Holocene. The oak species of the Zagros—Anti-Taurus Mts, particularly Quercus brantii Lindl., are strongly dependent on spring precipitation for regeneration and are sensitive to a long dry season. Detailed analysis of modern atmospheric circulation patterns in SW Asia during the late spring suggests that the Indian Summer Monsoon (ISM) intensification can modify the amount of late spring and/or early summer rainfall in western/northwestern Iran and eastern Anatolia, which could in turn have controlled the development of the Zagros—Anti-Taurus deciduous oak woodlands. During the early Holocene, the northwestward shift of the Inter-Tropical Convergence Zone (ITCZ) could have displaced the subtropical anticyclonic belt or associated high pressure ridges to the northwest. The latter could, in turn, have prevented the southeastward penetration of low pressure systems originating from the North Atlantic and Black Sea regions. Such atmospheric configuration could have reduced or eliminated the spring precipitation creating a typical Mediterranean continental climate characterized by winter-dominated precipitation. This scenario highlights the complexity of biome response to climate system interactions in transitional climatic and biogeographical regions.