Cloud Cover Feedback Moderates Fennoscandian Summer Temperature Changes Over the Past 1,000 Years

Abstract

Northern Fennoscandia has experienced little summer warming over recent decades, in stark contrast to the hemispheric trend, which is strongly linked to greenhouse gas emissions. A likely explanation is the feedback between cloud cover and temperature. We establish the long- and short-term relationships between summer cloud cover and temperature over Northern Fennoscandia, by analyzing meteorological and proxy climate data. We identify opposing feedbacks operating at different timescales. At short timescales, dominated by internal variability, the cloud cover-temperature feedback is negative; summers with increased cloud cover are cooler and sunny summers are warmer. However, over longer timescales, at which forced climate changes operate, this feedback is positive, rising temperatures causing increased regional cloud cover and vice versa. This has occurred both during warm (Medieval Climate Anomaly and at present) and cool (Little Ice Age) periods. This two-way feedback relationship therefore moderates Northern Fennoscandian temperatures during both warm and cool hemispheric periods.