Reversed Holocene temperature–moisture relationship in the Horn of Africa
Baxter, A.J.; Verschuren, D.; Peterse, F.; Miralles, D.G.; Martin-Jones, C.M.; Maitituerdi, A.; Van der Meeren, T.; Van Daele, M.; Lane, C.S.; Haug, G.H.; Olago, D.; Sinninghe Damsté, Jaap S.
(2023) Nature, volume 620, issue 7973, pp. 336 - 343
(Article)
Abstract
Anthropogenic climate change is predicted to severely impact the global hydrological cycle1, particularly in tropical regions where agriculture-based economies depend on monsoon rainfall2. In the Horn of Africa, more frequent drought conditions in recent decades3,4 contrast with climate models projecting precipitation to increase with rising temperature5. Here we use organic
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geochemical climate-proxy data from the sediment record of Lake Chala (Kenya and Tanzania) to probe the stability of the link between hydroclimate and temperature over approximately the past 75,000 years, hence encompassing a sufficiently wide range of temperatures to test the 'dry gets drier, wet gets wetter' paradigm6 of anthropogenic climate change in the time domain. We show that the positive relationship between effective moisture and temperature in easternmost Africa during the cooler last glacial period shifted to negative around the onset of the Holocene 11,700 years ago, when the atmospheric carbon dioxide concentration exceeded 250 parts per million and mean annual temperature approached modern-day values. Thus, at that time, the budget between monsoonal precipitation and continental evaporation7 crossed a tipping point such that the positive influence of temperature on evaporation became greater than its positive influence on precipitation. Our results imply that under continued anthropogenic warming, the Horn of Africa will probably experience further drying, and they highlight the need for improved simulation of both dynamic and thermodynamic processes in the tropical hydrological cycle.
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Keywords: Atmosphere/chemistry, Carbon Dioxide/analysis, Climate Change/history, Climate Models, Droughts/statistics & numerical data, Geologic Sediments/chemistry, History, Ancient, Humidity, Kenya, Lakes/chemistry, Rain, Tanzania, Temperature, Thermodynamics, Tropical Climate, Volatilization, Water Cycle, Water/analysis
ISSN: 0028-0836
Publisher: Nature Research
Note: Funding Information: This research was co-financed by NESSC Gravitation Grant 024.002.001 from the Dutch Ministry of Education, Culture and Science (OCW) to J.S.S.D.; by Ghent University Collaborative Research Operation grant BOF13/GOA/023, BRAIN-be project BR-121-A2 from the Belgian Science Policy Office (BelSPO), Hercules infrastructure grant AUGE/15/14-G0H2916N from the Research Foundation of Flanders, and a Francqui research professor mandate to D.V.; by UK Natural Environment Research Council standard grant NE/P011969/1 to C.S.L.; by the Max Planck Society to G.H.H.; and by the International Continental Scientific Drilling Program through the DeepCHALLA project (https://www.icdp-online.org/projects/world/africa/lake-challa/). D.G.M. acknowledges support from the European Research Council under grant agreement 101088405 ‘HEAT’ and the EU Horizon 2020 project 869550 ‘DOWN2EARTH’. A.M. was supported by a PhD scholarship from the Graduate Studies Authority and Department of Marine Geosciences at the University of Haifa. Recovery of the Lake Chala sediment record was facilitated by the government of Kenya through permit P/16/7890/10400 from the National Commission for Science, Technology and Innovation (NACOSTI), license EIA/PSL/3851 from the National Environmental Management Authority (NEMA), and research passes for foreign nationals issued by the Department of Immigration; and by the government of Tanzania through permits NA-2016-67 (270–285) and NA-2016-201 (277–292) from the Tanzania Commission for Science and Technology (COSTECH), permit EIA/10/0143/V.I/04 from the National Environmental Management Council, and resident permits issued by the Immigration Department. The lake-drilling operation was subject to environmental impact assessments conducted by Kamfor (Nairobi, Kenya) and Tansheq (Dar es Salaam, Tanzania), and permission from the Lands and Settlement Office of Taita-Taveta County (Kenya) to use government land as staging area. We thank all DeepCHALLA partners not directly involved in this work for project facilitation; C. M. Oluseno, the ‘Air Force One’ team, the Kamba and Taveta communities of Lake Chala area, and all field scientists for assisting in the lake-drilling operations; and the National Lacustrine Core Facility (LacCore) at the University of Minnesota (USA) for organizing the splitting, logging and initial processing of core samples. We further thank A. Mets and J. Riekenberg (NIOZ) for analysis of sedimentary biomarkers, I. Buisman (University of Cambridge) and E. Tomlinson (Trinity College Dublin) for tephra geochemical analyses, G. De Cort (Ghent University) for help with coding in R, I. Petrova (Ghent University) for providing CMIP6 climate model output, T. Markus (Utrecht University) for help with map drafting, and D. McLeod (Cardiff University) for feedback on the interpretation of hydroclimatic projections. Funding Information: This research was co-financed by NESSC Gravitation Grant 024.002.001 from the Dutch Ministry of Education, Culture and Science (OCW) to J.S.S.D.; by Ghent University Collaborative Research Operation grant BOF13/GOA/023, BRAIN-be project BR-121-A2 from the Belgian Science Policy Office (BelSPO), Hercules infrastructure grant AUGE/15/14-G0H2916N from the Research Foundation of Flanders, and a Francqui research professor mandate to D.V.; by UK Natural Environment Research Council standard grant NE/P011969/1 to C.S.L.; by the Max Planck Society to G.H.H.; and by the International Continental Scientific Drilling Program through the DeepCHALLA project ( https://www.icdp-online.org/projects/world/africa/lake-challa/ ). D.G.M. acknowledges support from the European Research Council under grant agreement 101088405 ‘HEAT’ and the EU Horizon 2020 project 869550 ‘DOWN2EARTH’. A.M. was supported by a PhD scholarship from the Graduate Studies Authority and Department of Marine Geosciences at the University of Haifa. Recovery of the Lake Chala sediment record was facilitated by the government of Kenya through permit P/16/7890/10400 from the National Commission for Science, Technology and Innovation (NACOSTI), license EIA/PSL/3851 from the National Environmental Management Authority (NEMA), and research passes for foreign nationals issued by the Department of Immigration; and by the government of Tanzania through permits NA-2016-67 (270–285) and NA-2016-201 (277–292) from the Tanzania Commission for Science and Technology (COSTECH), permit EIA/10/0143/V.I/04 from the National Environmental Management Council, and resident permits issued by the Immigration Department. The lake-drilling operation was subject to environmental impact assessments conducted by Kamfor (Nairobi, Kenya) and Tansheq (Dar es Salaam, Tanzania), and permission from the Lands and Settlement Office of Taita-Taveta County (Kenya) to use government land as staging area. We thank all DeepCHALLA partners not directly involved in this work for project facilitation; C. M. Oluseno, the ‘Air Force One’ team, the Kamba and Taveta communities of Lake Chala area, and all field scientists for assisting in the lake-drilling operations; and the National Lacustrine Core Facility (LacCore) at the University of Minnesota (USA) for organizing the splitting, logging and initial processing of core samples. We further thank A. Mets and J. Riekenberg (NIOZ) for analysis of sedimentary biomarkers, I. Buisman (University of Cambridge) and E. Tomlinson (Trinity College Dublin) for tephra geochemical analyses, G. De Cort (Ghent University) for help with coding in R, I. Petrova (Ghent University) for providing CMIP6 climate model output, T. Markus (Utrecht University) for help with map drafting, and D. McLeod (Cardiff University) for feedback on the interpretation of hydroclimatic projections. Publisher Copyright: © 2023, The Author(s).
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