Abstract
Climate variability is critically important for nature and society, especially if it increases in amplitude and/or fluctuations become more persistent. However, the issues of whether climate variability is changing, and if so, whether this is due to anthropogenic forcing, are subjects of ongoing debate. Increases in the amplitude and persistence of temperature fluctuations have been detected in some regions, e.g. the North Pacific, but there is no agreed global signal. Here we systematically scan monthly surface temperature indices and spatial datasets to look for trends in variance and autocorrelation (persistence). We show that monthly temperature variability and autocorrelation increased over 1957–2002 across large parts of the North Pacific, North Atlantic, North America and the Mediterranean. Furthermore, (multi)decadal internal climate variability appears to influence trends in monthly temperature variability and autocorrelation. Historically-forced climate models do not reproduce the observed trends in temperature variance and autocorrelation, consistent with the models poorly capturing (multi)decadal internal climate variability. Based on a review of established spatial correlations and corresponding mechanistic ‘teleconnections’ we hypothesise that observed slowing down of sea surface temperature variability contributed to observed increases in land temperature variability and autocorrelation, which in turn contributed to persistent droughts in North America and the Mediterranean.
Highlights
While the magnitude of long term change in the climate is important, society and ecosystems are sensitive to climate variability and its extremes
We started by analysing climate indices that have been derived from the dominant spatial patterns of variability in Northern Hemisphere sea surface temperature data, the Pacific Decadal Oscillation (PDO), the Atlantic Multi-decadal Oscillation (AMO), and the Atlantic Tripole
The latter represents the lagged response of ocean surface temperatures to the dominant mode of North Atlantic pressure variability, the North Atlantic Oscillation (NAO), which we analyse for completeness
Summary
While the magnitude of long term change in the climate is important, society and ecosystems are sensitive to climate variability and its extremes. In this study we set out to explore observed trends in the magnitude and persistence of climate variability These are of interest from both a social and an ecological perspective. We seek to extend previous global analyses that examined variance in annual mean temperature data[12, 13], by studying monthly temperature data for trends in lag-1 autocorrelation as well as variance (measured as standard deviation). This extends previous regional analysis[7], of monthly sea surface temperature data and the Pacific Decadal Oscillation index, to other regions and climate indices. We review existing studies in an attempt to mechanistically link some observed trends in the persistence of ocean surface temperature variability to observed extreme events on land
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