Abstract
Understanding natural climate variability is essential for assessments of climate change. This is reflected in the scaling properties of climate records. The scaling exponents of the interglacial and the glacial climates are fundamentally different. The Holocene record is monofractal, with a scaling exponent H∼0.7. On the contrary, the glacial record is multifractal, with a significantly higher scaling exponent H∼1.2, indicating a longer persistence time and stronger nonlinearities in the glacial climate. The glacial climate is dominated by the strong multi-millennial Dansgaard–Oeschger (DO) events influencing the long-time correlation. However, by separately analysing the last glacial maximum lacking DO events, here we find the same scaling for that period as for the full glacial period. The unbroken scaling thus indicates that the DO events are part of the natural variability and not externally triggered. At glacial time scales, there is a scale break to a trivial scaling, contrasting the DO events from the similarly saw-tooth-shaped glacial cycles.
Highlights
Understanding natural climate variability is essential for assessments of climate change
To identify the underlying dynamics reflected in scale breaks or robust scaling relations, records covering a large range of temporal scales are necessary
The Holocene is monofractal with a scaling exponent HB0.7, whereas the glacial climate is multifractal with H2B1.2
Summary
Understanding natural climate variability is essential for assessments of climate change. For understanding natural climate variability and the character of climate change, assessing correlation and persistence times is important These are reflected in the scaling properties of the climatic records. By filtering out the annual cycle, the scaling properties of temperature variations, covering four to five decades, have been investigated These indicate universal persistence laws for atmospheric variability[4], where station data from around the globe shows monofractal (Hurst)-scaling exponents around 0.7. This is significantly different from the value 0.5 characteristic for a trivial white noise process. It was in ice core records that it was first realized that the glacial climate was dominated by millennial scale instabilities, the Dansgaard–Oeschger (DO) events[9]. The cross-over time scale indicates the internal time scale of built-up of the large ice sheets
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