The results indicate that the majority of onshore Afro-Arabian sites experienced warming during the Medieval Climate Anomaly. The one exception was the southern Levant, which endured a cold phase during the same interval. From offshore records, the team also documented cooling in locations that currently experience cold-water upwellings but generally warmer conditions away from these upwelling zones during the same period.
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In some records, the researchers noted the presence of obvious cold spikes during intervals corresponding to decreased solar activity or declining ocean cycles. This, they argue, suggests that solar forcing and changing ocean circulation are the most likely causes of medieval era climate change.
This study represents a step toward globally characterizing the Medieval Climate Anomaly, an improved understanding of which will help scientists refine global climate models and improve hindcasting. To date, however, very few paleotemperature data exist from Afro-Arabia; the authors note that all of West Africa is currently represented by a single data point. Systematic research will be necessary to adequately reconstruct medieval paleotemperature patterns and their causes across this vast region. (Paleoceanography and Paleoclimatology, https://doi.org/10.1002/2017PA003237, 2017)
Warming and Cooling: The Medieval Climate Anomaly in Africa and Arabia
Sebastian Lüning, Mariusz Gałka, Fritz Vahrenholt
The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 Common Era. Here we present a palaeotemperature synthesis for the MCA in Africa and Arabia, based on 44 published localities. The data sets have been thoroughly correlated and the MCA trends palaeoclimatologically mapped. The vast majority of available Afro-Arabian onshore sites suggest a warm MCA, with the exception of the southern Levant where the MCA appears to have been cold. MCA cooling has also been documented in many segments of the circum-Africa-Arabian upwelling systems, as a result of changes in the wind systems which were leading to an intensification of cold water upwelling. Offshore cores from outside upwelling systems mostly show warm MCA conditions. The most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles. Conspicuous cold spikes during the earliest and latest MCA may help to discriminate between solar (Oort Minimum) and ocean cycle (Atlantic Multidecadal Oscillation, AMO) influence. Compared to its large share of nearly one quarter of the world’s landmass, data from Africa and Arabia are significantly underrepresented in global temperature reconstructions of the past 2,000 years. Onshore data are still absent for most regions in Africa and Arabia, except for regional data clusters in Morocco, South Africa, the East African Rift, and the Levant coast. In order to reconstruct land palaeotemperatures more robustly over Africa and Arabia, a systematic research program is needed.