Extreme Warming in the African Tropics during the Mid-Holocene: Environmental Impacts and Causal Mechanisms
Abstract
Holocene tropical climate variability is generally thought to consist of extremes in precipitation. Far less is known about extreme variations in tropical temperature. This is due in part to a lack of terrestrial temperature proxies, and in part to the assumed thermal stability of the tropics during the Holocene. Here we synthesize recent organic geochemical records of tropical African temperature, and present new records from high elevation African lakes, that document extreme warming of up to 3 ° C during the mid-Holocene. Peak temperatures occurred between 6 and 5 kyr BP, near the termination of the African Humid Period. Mid-Holocene warmth caused large environmental changes, particularly in montane environments. These include upslope migration of montane forests and the complete deglaciation of the Rwenzori Mountains, which until today hosts one of the few remaining glacier systems in Africa. Mid-Holocene warmth is not simulated by PMIP models, though the models do suggest that seasonal biases in proxy sensitivity could explain a fraction of this warming. But because mid-Holocene warming is not associated with increased radiative forcing, it must therefore result from internal feedbacks. Its timing, near the termination of the African Humid Period, suggests it could be linked to changes in the hydrological cycle, such as cloud cover, that influence surface temperatures. Whatever its cause, the mid-Holocene represents the most recent extreme warming in the tropics, and it is critical that we better understand its extent, underlying, mechanisms and impacts.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGC14A..02R
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3344 Paleoclimatology;
- ATMOSPHERIC PROCESSES;
- 1616 Climate variability;
- GLOBAL CHANGE;
- 1620 Climate dynamics;
- GLOBAL CHANGE