Large-scale Climate Change Research Articles

Australian water policy in a climate change context: some reflections

This paper focuses on Australian water reform in a climate change context over the period between mid-2006 and end 2011, with a particular focus on the Murray Darling Basin (MDB). In Australia, during this period, the potential impacts from climate change became more central to the policy debate, and the implementation of what can be said to be a large-scale climate change adaptation programme commenced. The paper outlines the policy framework adopted by the government of the day and then draws out some of the key issues for water management against this background, and the attendant increased uncertainty.

Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy

Abstract. Two lacustrine sediment cores from Lake Ledro in northern Italy were studied to produce chronologies of flood events for the past 10 000 yr. For this purpose, we have developed an automatic method that objectively identifies the sedimentary imprint of river floods in the downstream lake basin. The method was based on colour data extracted from processed core photographs, and the count data were analysed to capture the flood signal. Flood frequency and reconstructed sedimentary dynamics were compared with lake-level changes and pollen inferred vegetation dynamics. The results suggest a record marked by low flood frequency during the early and middle Holocene (10 000–4500 cal BP). Only modest increases during short intervals are recorded at ca. 8000, 7500, and 7100 cal BP. After 4500–4000 cal BP, the record shows a shift toward increased flood frequency. With the exception of two short intervals around 2900–2500 and 1800–1400 cal BP, which show a slightly reduced number of floods, the trend of increasing flood frequency prevailed until the 20th century, reaching a maximum between the 16th and the 19th centuries. Brief-flood frequency increases recorded during the early and middle Holocene can be attributed to cold climatic oscillations. On a centennial time scale, major changes in flood frequency, such as those observed after ca. 4500/4000 and 500 cal BP, can be attributed to large-scale climatic changes such as the Neo-glacial and Little Ice Age, which are under orbital and possibly solar control. However, in the Bronze Age and during the Middle Ages and modern times, forest clearing and land use probably partially control the flood activity.

Self-organized criticality of climate change

Self-organized criticality (SOC) of three climatic factors (average daily temperature, vapor pressure, and relative humidity) was studied by analyzing climate records from 1961 to 2011 in Yanqi County, northwest China. Firstly, we investigated the frequency-size distribution of three climatic factors and found that they were well approximated by power-law distribution, which suggested that climatic factor might be a manifestation of self-organized criticality. Furthermore, we introduced a new numerical sandpile model with decay coefficient to reveal inherent dynamic mechanism of climatic factor. Only changing the number value of decay coefficient of climatic factors, this model would give a good simulation of three climatic factors' statistical characteristics. This study showed that it was the self-organized criticality of the climate change that results in the temporal variation of climatic factors and the occurrence of large-scale climate change events triggered by SOC behavior of the minor climatic factors. So, we believed that SOC characteristics would have practical implications for climate prediction.

Top-Down Regulation, Climate and Multi-Decadal Changes in Coastal Zoobenthos Communities in Two Baltic Sea Areas

The structure of many marine ecosystems has changed substantially during recent decades, as a result of overexploitation, climate change and eutrophication. Despite of the apparent ecological and economical importance of coastal areas and communities, this aspect has received relatively little attention in coastal systems. Here we assess the temporal development of zoobenthos communities in two areas on the Swedish Baltic Sea coast during 30 years, and relate their development to changes in climate, eutrophication and top-down regulation from fish. Both communities show substantial structural changes, with a decrease in marine polychaetes and species sensitive to increased water temperatures. Concurrently, opportunistic species tolerant to environmental perturbation have increased in abundance. Species composition show a similar temporal development in both communities and significant changes in species composition occurred in both data sets in the late 1980s and early 1990s. The change in species composition was associated with large scale changes in climate (salinity and water temperature) and to the structure of the local fish community, whereas we found no effects of nutrient loading or ambient nutrient concentrations. Our results suggest that these coastal zoobenthos communities have gone through substantial structural changes over the last 30 years, resulting in communities of different species composition with potentially different ecological functions. We hence suggest that the temporal development of coastal zoobenthos communities should be assessed in light of prevailing climatic conditions considering the potential for top-down effects exerted by local fish communities.

A comparison of recent changes in distribution of capelin (Mallotus villosus) in the Barents Sea, around Iceland and in the Northwest Atlantic

Capelin stocks in the Barents Sea, around Iceland and off eastern Newfoundland and Labrador have traditionally undergone similar basic migration patterns, from southern spawning sites to more northern feeding locations. In this paper, the migration and distribution patterns are reviewed for the three stocks. Special attention is paid to the relatively recent past, when Icelandic and Newfoundland/Labrador stocks exhibited changes in these patterns, while the Barents Sea stock did not undergo any significant distributional change. The changes occurred first off Newfoundland/Labrador and later in Icelandic waters. We examine the possible role of temperature and stock abundance in controlling capelin migration and distribution through comparisons of the three stocks. From the available observations, it is not possible to determine the relative impacts of temperature and abundance. However, all three areas have exhibited significant warming trend and we suggest that capelin may be reacting to large-scale ocean climate changes that have been occurring in the Arctic as a result of global warming. We speculate that such changes should appear first off Newfoundland/Labrador because this area is more heavily dominated by waters from the Arctic. In contrast, while both the Barents Sea and Icelandic areas are influenced by waters of Arctic origin, they also receive a significant input of warmer, Atlantic waters. The appearance of capelin in the Canadian Arctic is consistent with the movement towards the Arctic and/or an increase in abundance of a subarctic species previously at the margins of its historical distribution, under conditions of increasing ocean temperatures in the Arctic.

The influence of inter-annually varying albedo on regional climate and drought

Albedo plays an important role in land–atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land–atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land–atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a strengthening of the second mechanism. That is, the second mechanism is stronger in a drought year compared to a normal year and this difference is larger than for the first mechanism. When both mechanisms are active, the second mechanism tends to dominate across the model domain, particularly during the 2002 drought period. The introduction of observed inter-annual variations in albedo produces an enhancement of the first mechanism and a weakening of the second mechanism during the onset of the drought.

Cervids in a dynamic northern landscape: Holocene changes in the relative abundance of moose and red deer at the limits of their distributions

It is predicted that future climate change will have a significant impact on the distribution of large ungulates on a continental scale. At the same time, changes in human land use on a more local scale may affect their distribution and dispersal abilities, possibly confounding the effects of climate. We analyze changes in the Holocene distribution and relative abundance of Alces alces (moose) and Cervus elaphus (red deer) skeletal remains along an overlapping range boundary of these species in western Norway. As moose and red deer are adapted to different climatic conditions we would expect the distribution of finds to reflect large-scale changes in climate. In accordance with this prediction our results indicate that red deer became the predominant ungulate in this area during the mid-Holocene warm period, c. 8000–4000 cal. BP. Contrary to this, remains of moose became even less abundant in the subsequent colder period to the present. This decrease seems tied to the spread of agriculture and deforestation, indicating the importance of considering changes in land use when predicting future changes in ungulate distribution.

Plantation forests, climate change and biodiversity

Nearly 4 % of the world’s forests are plantations, established to provide a variety of ecosystem services, principally timber and other wood products. In addition to such services, plantation forests provide direct and indirect benefits to biodiversity via the provision of forest habitat for a wide range of species, and by reducing negative impacts on natural forests by offsetting the need to extract resources. There is compelling evidence that climate change is directly affecting biodiversity in forests throughout the world. These impacts occur as a result of changes in temperature, rainfall, storm frequency and magnitude, fire frequency, and the frequency and magnitude of pest and disease outbreaks. However, in plantation forests it is not only the direct effects of climate change that will impact on biodiversity. Climate change will have strong indirect effects on biodiversity in plantation forests via changes in forest management actions that have been proposed to mitigate the effects of climate change on the productive capacity of plantations. These include changes in species selection (including use of species mixtures), rotation length, thinning, pruning, extraction of bioenergy feedstocks, and large scale climate change driven afforestation, reforestation, and, potentially deforestation. By bringing together the potential direct and indirect impacts of climate change we conclude that in the short to medium term changes in plantation management designed to mitigate or adapt to climate change could have a significantly greater impact on biodiversity in such plantation forests than the direct effects of climate change. Although this hypothesis remains to be formally tested, forest managers worldwide are already considering new approaches to plantation forestry in an effort to create forests that are more resilient to the effects of changing climatic conditions. Such change presents significant risks to existing biodiversity values in plantation forests, however it also provides new opportunities to improve biodiversity values within existing and new plantation forests. We conclude by suggesting future options, such as functional zoning and species mixtures applied at either the stand level or as fine-scale mosaics of single-species stands as options to improve biodiversity whilst increasing resilience to climate change.

Anisotropy of magnetic susceptibility and sedimentary cycle data from Permo-Carboniferous rhythmites (Paraná Basin, Brazil): a multiple proxy record of astronomical and millennial scale palaeoclimate change in a glacial setting

Abstract In this study we examine glaciogenic rhythmites from the Late Palaeozoic Itararé Group, Paraná Basin, Brazil. We conduct spectral analysis on lithological cycle (‘couplet’) thickness series, and declination of maximum axis of anisotropy of magnetic susceptibility ellipsoidal tensor (K1) data. We tested the efficiency of K1 as a palaeoclimatic proxy. To constrain the timescale of harmonic features in the data, we analysed the couplet thickness spectra, converting the spectra to the time domain using an astronomical calibration based on Milankovitch frequency ratios. Comparison of the two rhythmites provides insights into their sedimentation rate evolution and cyclicity. Millennial-scale mechanisms of climatic origin influenced the deposition of both rhythmites, generating the lithological couplets, and are consistent with millennial-scale variations recognized as triggers for large-scale climatic changes during the Late Pleistocene. The common harmonic features in the couplet thickness and K1 spectra support the view that the azimuth of the K1 axis in sedimentary fabric is a useful palaeoclimatic proxy, reflecting sedimentation processes that were directly influenced by flow-induced, sediment transport, which is linked to external climate factors.

Palaeoenvironmental dynamics and underlying climatic changes in southeast Amazonia (Serra Sul dos Carajás, Brazil) during the late Pleistocene and Holocene

Pollen, fern spore, micro-charcoal, sediment and mineral analyses have been carried out on a 466cm-long sediment core from the Serra Sul dos Carajás swamp in southeastern Amazonia. Ten AMS radiocarbon dates suggest that the sediment covers at least the last 73,000years. Shifts between tropical forests and savanna, changes in species composition, as well as changes in fire frequency indicate several wet and dry periods during this time interval. During the assumed early Pleniglacial (73–50ka), the dominance of savanna vegetation reflects drier conditions, whereas vegetation changes in the mid-Pleniglacial (50–40ka) suggest alternating wet and dry phases under generally cool conditions. The recorded next period before the Last Glacial Maximum (LGM) shows a transition to wetter and cooler conditions, followed by a cold and dry LGM and Late glacial. At the beginning of the Holocene, between 11.4 and 10.2calka, tropical forest expanded, reflecting stable and very humid conditions. During the early to mid-Holocene an increasingly seasonal, generally warm and dry climate established. Dry seasons were longer than at present during mid-Holocene times with a pronounced dry phase from 9 to 3.4calka. Only after 3.4calka did modern tropical rainforests became established under present-day climatic conditions. Comparison with other palaeoecological studies in the Amazon basin and eastern Andean regions suggests that environmental changes in Serra Sul were strongly coupled with large scale climatic changes and sea surface temperature variability in the tropical Atlantic.

Interacting effects of wildfire severity and liming on nutrient cycling in a southern Appalachian wilderness area

Aims Wilderness and other natural areas are threatened by large-scale disturbances (e.g., wildfire), air pollution, climate change, exotic diseases or pests, and a combination of these stress factors (i.e., stress complexes). Linville Gorge Wilderness (LGW) is one example of a high elevation wilderness in the southern Appalachian region that has been subject to stress complexes including chronic acidic deposition and several wildfires, varying in intensity and extent. Soils in LGW are inherently acidic with low base cation concentrations and decades of acidic deposition have contributed to low pH, based saturation, and Ca:Al ratio. We hypothesized that wildfires that occurred in LGW followed by liming burned areas would accelerate the restoration of acidic, nutrient depleted soils. Because soils at LGW had extremely low concentrations of exchangeable Ca 2+ and Mg 2+ dolomitic lime was applied to further boost these cations. We evaluated the effectiveness of dolomitic lime application in restoring exchangeable Ca 2+ and Mg 2+ and subsequently increasing pH and Ca:Al ratio of soils and making Ca and Mg available to recovering vegetation. Methods Five treatment areas were established: severely burned twice (2000 & 2007) with dolomitic lime application (2xSBL); moderately burned twice with lime application (2xMBL); severely burned twice, unlimed (2xSB); moderately burned once (2000), unlimed (1xMB); and a reference area (REF; unburned, unlimed). In 2008 and 2009, we measured overstory, understory, and ground-layer vegetation; forest floor mass and nutrients; and soil and soil solution chemistry within each treatment area. Results All wildfire burned sites experienced substantial overstory mortality. However, understory biomass doubled between sample years on the most recently burned sites due to the rapid regrowth of ericaceous shrubs and prolific sprouting of deciduous trees. Burning followed by lime application (2xSBL and 2xMBL) significantly increased shallow soil solution NO3-N, but we found no soil solution NO3-N response to burning alone (2xSB and 1xMB). Surface soil base saturation and exchangeable Ca 2+ were significantly affected by liming; Ca 2+ concentrations were greater on 2xMBL and 2xSBL than 2xSB, 1xMB and REF.

Diversity of plant evolutionary lineages promotes arthropod diversity

Large-scale habitat destruction and climate change result in the non-random loss of evolutionary lineages, reducing the amount of evolutionary history represented in ecological communities. Yet, we have limited understanding of the consequences of evolutionary history on the structure of food webs and the services provided by biological communities. Drawing on 11 years of data from a long-term plant diversity experiment, we show that evolutionary history of plant communities - measured as phylogenetic diversity - strongly predicts diversity and abundance of herbivorous and predatory arthropods. Effects of plant species richness on arthropods become stronger when phylogenetic diversity is high. Plant phylogenetic diversity explains predator and parasitoid richness as strongly as it does herbivore richness. Our findings indicate that accounting for evolutionary relationships is critical to understanding the severity of species loss for food webs and ecosystems, and for developing conservation and restoration policies.

Severe tornadoes on the Caribbean coast of Colombia since 2001 and their relation to local climate conditions

Tornadoes have been reported in various places around the world. The United States has the greatest number of tornado reports. In South America, tornadoes have been reported in Argentina and neighboring countries, such as Chile, Brazil, and Uruguay. There are no reports of tornadoes in Colombia in the worldwide databases. The first reported tornado event in Colombia took place in 2001. Since then, four tornados have affected the northern part of Colombia. The aim of this study is to characterize the events reported on the Caribbean coast of Colombia and their relation to local climate conditions. Before 2001, we had no knowledge regarding tornadoes in this area. However, during the past 10 years, these atmospheric phenomena have occurred in Barranquilla and the surrounding metropolitan area. Worldwide databases on tornadoes have not registered any such events in this part of South America. A review of the atmospheric information was conducted to determine the influence of air temperature increases on tornado formation. This study reveals that tornadoes have appeared between May and September, the months during which the city experiences the hottest temperatures of the year. The most significant tornado took place on September 15, 2006. This tornado lasted 15 min and travelled almost 10 km. Of the four registered tornadoes, this was the only one to affect the residential area of the city. The other three affected only the suburbs located in the surrounding metropolitan area. The most recent phenomenon related with tornadoes took place between July and August of 2010, during which three tornadoes could have potentially formed. However, a vortex never made contact with the ground. This meteorological analysis is very basic because climate information for these areas is limited. Still, what information we have reveals conditions that are typical of tornado formation: a mass of cold air combined with high air temperatures in a specific area. The data analysis reveals that tornados have occurred between May and June. These months correspond to the period characterized by the highest temperatures: average temperatures of 28.2 °C and maximum temperatures of 33.2 °C. This is also the period characterized by the greatest relative humidity and precipitation (84 % and 50 mm, respectively). Because the tornadoes reports only appeared in the last 10 years, it is not possible to determine whether there is a realistic relationship between their occurrence and large-scale climatic change. This article characterizes tornadoes as a new environmental threat and not an isolated phenomenon for this part of Colombia. Tornadoes in this region should thus be included in global databases.

The Scope for Reducing Emissions from Forestry and Agriculture in the Brazilian Amazon

Reducing emissions from agriculture, forestry, and other land uses is considered an essential ingredient of an effective strategy to mitigate global warming. Required changes in land use and forestry, however, often imply foregoing returns from locally more attractive resource use strategies. We assess and compare the prospects of mitigating climate change through emission reductions from forestry and agriculture in the Brazilian Amazon. We use official statistics, literature, and case study material from both old and new colonization frontiers to identify the scope for emission reductions, in terms of potential additionality, opportunity costs, technological complexity, transaction costs, and risks of economic and environmental spillover effects. Our findings point to a comparative advantage in the Brazilian Amazon of forest conservation-based over land-use modifying mitigation options, especially in terms of higher potential additionality in emission reductions. Low-cost mitigation options do exist also in use-modifying agriculture and forestry, but tend to be technologically complex thus requiring more costly intervention schemes. Our review points to a series of regional development deficits that may come to hamper attempts to tap into the large-scale climate change mitigation potential often associated with the Amazon. Low-hanging fruits for mitigation do exist, but must be carefully identified based on the performance indicators we discuss.

Climatic, landform, microtopographic, and overstory canopy controls of tree invasion in a subalpine meadow landscape, Oregon Cascades, USA

Tree invasions have been documented throughout Northern Hemisphere high elevation meadows, as well as globally in many grass and forb-dominated ecosystems. Tree invasions are often associated with large-scale changes in climate or disturbance regimes, but are fundamentally driven by regeneration processes influenced by interactions between climatic, topographic, and biotic factors at multiple spatial scales. The purpose of this research was to quantify spatiotemporal patterns of meadow invasion; and how climate, larger landforms, topography, and overstory trees have interactively influenced tree invasion. We combined airborne Light Detection and Ranging (LiDAR) characterizations of landforms, topography, and overstory vegetation with historical climate, field measurements of snow depth, tree abundance, and tree ages to reconstruct spatial and temporal patterns of tree invasion over five decades in a subalpine meadow complex in the Oregon Cascade Range, USA. Proportion of meadow occupied by trees increased from 8 % in 1950 to 35 % in 2007. Larger landforms, topography, and tree canopies interactively mediated regional climatic controls of tree invasion by modifying depth and persistence of snow pack, while tree canopies also influenced seed source availability. Landscape context played an important role mediating snow depth and tree invasion; on glacial landforms tree invasion was negatively associated with spring snowfall, but on debris flows tree invasion was not associated with snow fall. The importance of snow, uncertain climate change impacts on snow, and mediation of snow by interacting and context dependent factors in complex mountain terrain poses substantial hurdles for understanding how these ecotones may respond to future climate conditions.

Changes in the summertime atmospheric circulation over East Asia and formation of long-lasting low-water periods within the Selenga river basin

We examine the formation patterns of the low-water periods 1976–1982 and 1996–2011 for the Selenga river. One of the immediate reasons for the low-water periods under consideration is the attenuation of the circulation in the zone of convergence of monsoon flows and mid-latitude flows over Mongolia and North China. Unlike the low-water periods of the preceding decades, a decrease in precipitation amounts during the current low-water period is taking place concurrently with large-scale climatic changes.

Widespread Climate Change in the Himalayas and Associated Changes in Local Ecosystems

BackgroundClimate change in the Himalayas, a biodiversity hotspot, home of many sacred landscapes, and the source of eight largest rivers of Asia, is likely to impact the well-being of ∼20% of humanity. However, despite the extraordinary environmental, cultural, and socio-economic importance of the Himalayas, and despite their rapidly increasing ecological degradation, not much is known about actual changes in the two most critical climatic variables: temperature and rainfall. Nor do we know how changes in these parameters might impact the ecosystems including vegetation phenology.Methodology/Principal FindingsBy analyzing temperature and rainfall data, and NDVI (Normalized Difference Vegetation Index) values from remotely sensed imagery, we report significant changes in temperature, rainfall, and vegetation phenology across the Himalayas between 1982 and 2006. The average annual mean temperature during the 25 year period has increased by 1.5°C with an average increase of 0.06°C yr−1. The average annual precipitation has increased by 163 mm or 6.52 mmyr−1. Since changes in temperature and precipitation are immediately manifested as changes in phenology of local ecosystems, we examined phenological changes in all major ecoregions. The average start of the growing season (SOS) seems to have advanced by 4.7 days or 0.19 days yr−1 and the length of growing season (LOS) appears to have advanced by 4.7 days or 0.19 days yr−1, but there has been no change in the end of the growing season (EOS). There is considerable spatial and seasonal variation in changes in climate and phenological parameters.Conclusions/SignificanceThis is the first time that large scale climatic and phenological changes at the landscape level have been documented for the Himalayas. The rate of warming in the Himalayas is greater than the global average, confirming that the Himalayas are among the regions most vulnerable to climate change.

Examining the Origin of Fortifications in East Timor: Social and Environmental Factors

ABSTRACT The remains of fortified archaeological sites abound in hilltop locations on the island of East Timor (Timor-Leste). Archaeologists have linked the emergence of these fortified settlements with environmental change. Some point to a period of reduced rainfall and increased environmental fluctuations beginning about AD 1000, while others cite relatively large-scale climate change during the post-AD 1300 transition from the Medieval Warm Period to the Little Ice Age. Both groups link environmental change to resource unpredictability which in turn leads to inter-group conflict. Of course environmental change is not the only possible trigger for conflict; a variety of social or economic factors could also be responsible. Here we present data on three fortified sites in East Timor, two of which have been dated, and combine these new data with previous work to develop a new chronology for fortifications in eastern East Timor. We then evaluate potential environmental and social factors against this chronology and other archaeological, historical, and ethnohistoric evidence. This assessment indicates that social factors, particularly the impact of increased sandalwood trade, were likely more important drivers of fortification and conflict in East Timor than environmental change.

The environmental context for the origins of modern human diversity: A synthesis of regional variability in African climate 150,000–30,000 years ago

We synthesize African paleoclimate from 150 to 30 ka (thousand years ago) using 85 diverse datasets at a regional scale, testing for coherence with North Atlantic glacial/interglacial phases and northern and southern hemisphere insolation cycles. Two major determinants of circum-African climate variability over this time period are supported by principal components analysis: North Atlantic sea surface temperature (SST) variations and local insolation maxima. North Atlantic SSTs correlated with the variability found in most circum-African SST records, whereas the variability of the majority of terrestrial temperature and precipitation records is explained by local insolation maxima, particularly at times when solar radiation was intense and highly variable (e.g., 150–75 ka). We demonstrate that climates varied with latitude, such that periods of relatively increased aridity or humidity were asynchronous across the northern, eastern, tropical and southern portions of Africa. Comparisons of the archaeological, fossil, or genetic records with generalized patterns of environmental change based solely on northern hemisphere glacial/interglacial cycles are therefore imprecise.We compare our refined climatic framework to a database of 64 radiometrically-dated paleoanthropological sites to test hypotheses of demographic response to climatic change among African hominin populations during the 150–30 ka interval. We argue that at a continental scale, population and climate changes were asynchronous and likely occurred under different regimes of climate forcing, creating alternating opportunities for migration into adjacent regions. Our results suggest little relation between large scale demographic and climate change in southern Africa during this time span, but strongly support the hypothesis of hominin occupation of the Sahara during discrete humid intervals ∼135–115 ka and 105–75 ka. Hominin populations in equatorial and eastern Africa may have been buffered from the extremes of climate change by locally steep altitudinal and rainfall gradients and the complex and variable effects of increased aridity on human habitat suitability in the tropics. Our data are consistent with hominin migrations out of Africa through varying exit points from ∼140–80 ka.

Juvenile dispersal affects straying behaviors of adults in a migratory population

The resilience of organisms to large-scale environmental and climatic change depends, in part, upon the ability to colonize and occupy new habitats. While previous efforts to describe homing, or natal site fidelity, of migratory organisms have been hindered by the confounding effects of fragmented landscapes and management practices, realistic conservation efforts must include considerations of the behavioral diversity represented by animal movements and dispersal. Herein, we quantify straying away from natal origins by adult chinook salmon (Oncorhynchus tshawytscha) in a wild population that inhabits a pristine wilderness basin. Using natural isotopic signatures (7Sr/86Sr) to reconstruct the migratory behaviors of unhandled individuals over their entire life cycle, we identified ecological and behavioral factors influencing the propensity to stray. Our results indicate that natal site fidelity is scale dependent, ranging from 55% at -1-km distances to 87% at longer (> 10-km scale) distances, and juvenile dispersal and sex highly influence straying occurrence. These findings lend support for the conservation of behavioral diversity for population persistence, and we propose straying as a mechanism for maintaining genetic diversity at low population densities.