Climate Conundrum: A Wet or Dry European and Northern African Climate During the Middle Miocene

• Published in: Geophysical research letters Vol. 51; no. 21
• Main Authors: Acosta, R. P., Burls, N. J., Pound, M. J., Bradshaw, C. D., McCoy, J., Gibson, M., O’Keefe, J. M. K., Feakins, S. J.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-11-2024; American Geophysical Union (AGU); Wiley
• Subjects: African monsoon; Boundary conditions; Carbon dioxide; Carbon dioxide concentration; Climate change; Climate models; Climate prediction; continental paleoclimate records; Data comparison; Drying; Evaporation; Fossils; global climate models; Global warming; Hydroclimate; Mediterranean climate; middle Miocene; Miocene; Mixed forests; Monsoon rainfall; Oceans; Paleobotany; paleoclimate; Precipitation; Rainfall; Regional climates; Regions; Sea surface temperature; Sea surface warming; Subtropical climates; Surface temperature; Vegetation; Warm climates; Water vapor; Water vapor flux; Water vapour; Europe; North Africa
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL109499

End of 21st‐century hydroclimate projections suggest an expansion of subtropical dry zones, with Mediterranean and Sahel regions becoming much drier. However, paleobotanical assemblage evidence from the middle Miocene (17‐12 Ma), suggests both regions were instead humid environments. Here we show that by modifying regional sea surface temperatures (SST) in an Earth System Model (CESM1.2) simulation of the middle Miocene, the increased ocean evaporation and integrated water vapor flux overrides any drying effects associated with warming‐induced land‐surface evaporation driven by atmospheric CO2 concentrations. These modifications markedly reduce the bias in the model‐data comparison for this period. A vegetation model (BIOME4) forced with simulated climatologies predicts both regions were dominated by mixed forest, which is largely consistent with the paleobotanical record. This study unveils the potential for wetter subtropical Mediterranean climates associated with warming, presenting an alternative scenario from future drying projections with localized SST warming governing regional climate change.
Plain Language Summary
Climate models project drier conditions over Europe and Northern Africa due to global warming. However, evidence from a past warm climate period, the middle Miocene (∼15 million years ago), finds wetter rather than drier environments. We refine climate model boundary conditions by reconstructing warmer ocean waters in the North Atlantic based on proxy evidence. The warmer ocean produces wetter environments by enhancing North Atlantic precipitation events and the North African monsoon. The increased rainfall and surface temperature cause a vegetation model to predict more forest coverage over Europe and Northern Africa, which is consistent with fossil evidence from ∼15 million years ago. This study unveils the potential for wetter climates associated with warming, presenting an alternative scenario from future drying projections, with localized sea surface warming governing regional climate.
Key Points
Middle Miocene Europe rainfall discrepancy between herpetological (dry) and paleobotanical (wet) records complicate climate model validation
Simulations that produce dry environments also produce cool North Atlantic sea surface temperatures which are inconsistent with proxies
SSTs informed by North Atlantic proxies produce wetter environments consistent with paleobotanical evidence