Search

Thermophilization is the directional change in species community composition towards greater relative abundances of species associated with warmer environments. This process is well-documented in temperate and Neotropical plant communities, but it is uncertain whether this phenomenon occurs elsewhere in the tropics. Here we extend the search for thermophilization to equatorial Africa, where lower tree diversity compared to other tropical forest regions and different biogeographic history could affect community responses to climate change. Using re-census data from 17 forest plots in three mountain regions of Africa, we find a consistent pattern of thermophilization in tree communities. Mean rates of thermophilization were +0.0086 °C·y−1 in the Kigezi Highlands (Uganda), +0.0032 °C·y−1 in the Virunga Mountains (Rwanda-Uganda-Democratic Republic of the Congo) and +0.0023 °C·y−1 in the Udzungwa Mountains (Tanzania). Distinct from other forests, both recruitment and mortality were important drivers of thermophilzation in the African plots. The forests studied currently act as a carbon sink, but the consequences of further thermophilization are unclear. Thermophilization is a change in species community composition towards greater abundances of species associated with warmer environments. This study provides evidence of thermophilization in understudied Afromontane forests, but with drivers that are distinct from other forest types. [ABSTRACT FROM AUTHOR]

The global population is aging at the same time as heat exposures are increasing due to climate change. Age structure, and its biological and socio-economic drivers, determine populations' vulnerability to high temperatures. Here we combine age-stratified demographic projections with downscaled temperature projections to mid-century and find that chronic exposure to heat doubles across all warming scenarios. Moreover, >23% of the global population aged 69+ will inhabit climates whose 95th percentile of daily maximum temperature exceeds the critical threshold of 37.5 °C, compared with 14% today, exposing an additional 177–246 million older adults to dangerous acute heat. Effects are most severe in Asia and Africa, which also have the lowest adaptive capacity. Our results facilitate regional heat risk assessments and inform public health decision-making. By 2050 > 23% of the global population aged 69 + will live in climates with acute heat exposure– the 95th percentile of the distribution of maximum daily temperatures–greater than the critical threshold of 37.5C, compared with 14% in 2020, an increase of 177–246 million older adults exposed to dangerous acute heat. [ABSTRACT FROM AUTHOR]

The consistent monitoring of trees both inside and outside of forests is key to sustainable land management. Current monitoring systems either ignore trees outside forests or are too expensive to be applied consistently across countries on a repeated basis. Here we use the PlanetScope nanosatellite constellation, which delivers global very high-resolution daily imagery, to map both forest and non-forest tree cover for continental Africa using images from a single year. Our prototype map of 2019 (RMSE = 9.57%, bias = −6.9%). demonstrates that a precise assessment of all tree-based ecosystems is possible at continental scale, and reveals that 29% of tree cover is found outside areas previously classified as tree cover in state-of-the-art maps, such as in croplands and grassland. Such accurate mapping of tree cover down to the level of individual trees and consistent among countries has the potential to redefine land use impacts in non-forest landscapes, move beyond the need for forest definitions, and build the basis for natural climate solutions and tree-related studies. Recent analyses have suggested that tree cover in non-forest ecosystems may be much higher than expected. Here, the authors map tree cover down to the individual tree level for the entire continent of Africa and find that almost 30% is found outside areas classified as forests. [ABSTRACT FROM AUTHOR]

Evaluating the impact and implications of eolian repositories that mark large-scale climatic transitions requires knowledge about the timing of their emplacement and the mechanisms responsible for their production, which remain highly uncertain. Here we apply numerical modeling of cosmogenic nuclide data, measured in the largest continuous terrestrial body of sand on Earth, to determine settings under which the sand was generated, by constraining the timing of sand introduction into the interior of southern Africa. Our findings reveal that major events of sand formation and accumulation in the Kalahari Basin occurred between ~2.2 and 1 Myr ago. The establishment of the Kalahari sand field corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for flora, fauna, and hominins in southern Africa during the Pleistocene. Modeling cosmogenic nuclides concentrations from Kalahari Desert Sand reveals the time of sand introduction into the landscape. This coincides with morphotectonic and climatic changes that could have triggered sand production and its impact on the environment. [ABSTRACT FROM AUTHOR]

Precipitation-based assessments show a lengthening of tropical dry seasons under climate change, without considering simultaneous changes in ecosystem water demand. Here, we compare changes in tropical dry season length and timing when dry season is defined as the period when precipitation is less than: its climatological average, potential evapotranspiration, or actual evapotranspiration. While all definitions show more widespread tropical drying than wetting for 1983-2016, we find the largest fraction (48.7%) of tropical land probably experiencing longer dry seasons when dry season is defined as the period when precipitation cannot meet the need of actual evapotranspiration. Southern Amazonia (due to delayed end) and central Africa (due to earlier onset and delayed end) are hotspots of dry season lengthening, with greater certainty when accounting for water demand changes. Therefore, it is necessary to account for changing water demand when characterizing changes in tropical dry periods and ecosystem water deficits. Changing precipitation pattern has been suggested to expand tropical dry seasons. Here, the authors show that this lengthening can be even more severe when accounting for the simultaneous rise of ecosystem water demand in a warmer climate. [ABSTRACT FROM AUTHOR]

Droughts that exceed the magnitudes of historical variation ranges could occur increasingly frequently under future climate conditions. However, the time of the emergence of unprecedented drought conditions under climate change has rarely been examined. Here, using multimodel hydrological simulations, we investigate the changes in the frequency of hydrological drought (defined as abnormally low river discharge) under high and low greenhouse gas concentration scenarios and existing water resource management measures and estimate the time of the first emergence of unprecedented regional drought conditions centered on the low-flow season. The times are detected for several subcontinental-scale regions, and three regions, namely, Southwestern South America, Mediterranean Europe, and Northern Africa, exhibit particularly robust results under the high-emission scenario. These three regions are expected to confront unprecedented conditions within the next 30 years with a high likelihood regardless of the emission scenarios. In addition, the results obtained herein demonstrate the benefits of the lower-emission pathway in reducing the likelihood of emergence. The Paris Agreement goals are shown to be effective in reducing the likelihood to the unlikely level in most regions. However, appropriate and prior adaptation measures are considered indispensable when facing unprecedented drought conditions. The results of this study underscore the importance of improving drought preparedness within the considered time horizons. Significant regional disparities exist in the time left to prepare for unprecedented drought and how much we can buy time depending on climate scenarios. Specific regions pass this timing by the middle of 21st century even with stringent mitigation. [ABSTRACT FROM AUTHOR]

Agroforestry systems have the potential to sequester carbon and offer numerous benefits to rural communities, but their capacity to offer valuable cooling services has not been quantified on continental scales. Here, we find that trees in pasturelands ("silvopasture") across Latin America and Africa can offer substantial cooling benefits. These cooling benefits increase linearly by −0.32 °C to −2.4 °C per 10 metric tons of woody carbon per hectare, and importantly do not depend on the spatial extent of the silvopasture systems. Thus, even smallholders can reap important cooling services from intensifying their silvopasture practices. We then map where realistic (but ambitious) silvopasture expansion could counteract a substantial fraction of the local projected warming in 2050 due to climate change. Our findings indicate where and to what extent silvopasture systems can counteract local temperature increases from global climate change and help vulnerable communities adapt to a warming world. A new study shows that tropical silvopasture systems can provide significant cooling services for local communities, and identifies where these silvopasture systems can most effectively counteract global climate change to help communities adapt to warming. [ABSTRACT FROM AUTHOR]