Abstract
AbstractThe past provides evidence of abrupt climate shifts and changes in the frequency of climate and weather extremes. We explore the nonlinear response to orbital forcing and then consider climate millennial variability down to daily weather events. Orbital changes are translated into regional responses in temperature, where the precessional response is related to nonlinearities and seasonal biases in the system. We question regularities found in climate events by analyzing the distribution of interevent waiting times. Periodicities of about 900 and 1,150 yr are found in ice cores besides the prominent 1,500 yr cycle. However, the variability remains indistinguishable from a random process, suggesting that centennial‐to‐millennial variability is stochastic in nature. New numerical techniques are developed allowing for a high resolution in the dynamically relevant regions like coasts, major upwelling regions, and high latitudes. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large‐scale ocean circulation, whereas subpolar hosing mimicking icebergs yields a quasi shutdown. The same multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores. Finally, abrupt climate events also have counterparts in the recent climate records, revealing a close link between climate variability, the statistics of North Atlantic weather patterns, and extreme events.
Highlights
Weather and climate vary on broad ranges of spatial and temporal scales
The precessional response is related to nonlinearities and/or seasonal biases in the climate system
The generation of low-frequency variability in the climate system is crucial to allow a separation of anthropogenic signals from natural variability, thereby increasing the ability to recognize and improve the attribution of climate and weather events to anthropogenic climate change
Summary
Weather and climate vary on broad ranges of spatial and temporal scales. This is evident from observations and simulations of the present climate as well as from climate history as recorded in geological and glaciological archives (Bradley, 2014; Crowley & North, 1991; Mitchell, 1976; Saltzman, 2002). Solid freshwater (calving ice bergs) could have been transported off the coasts affecting deep water formation effectively This sensitivity is essential to understand past and potential future abrupt climate changes related to freshening of the North Atlantic Ocean (e.g., Kjeldsen et al, 2015; Sejr et al, 2017). High-resolution models are required to elucidate the causal chains in the climate system, notably during abrupt transitions of the last deglaciation, and provide a benchmark for future transitions under rapid CO2 increase (cf Figure 2c) Another way to ascertain the extent of past changes is through the inspection of historical time series of direct temperature measurements or documentation of such environmental observations. We further propose future research directions for studying climate changes regarding sampling strategies, statistical tools, and the formulation of climate models, reviewing the challenges to understand the causes and contributors to climate shifts and extremes
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