Abrupt Climate and Weather Changes Across Time Scales

Abstract

The 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. Plain Language Summary Predicting the future spread of possible climates, the risk of climate extremes and the risk of rapid transitions is of high socioeconomic relevance. The past provides evidence of abrupt climate change and the frequency of extremes. This allows to separate anthropogenic signals from natural climate variability. Earth system models applied both to past and future scenarios will enhance our ability to detect regime shifts which are necessary to potentially predict climate extremes and transitions. We consider the response of the system to regular orbital forcing and then focus on shorter time scales down to weather. The appearance of precession is linked to nonlinear responses of the climate system to external orbital forcing. Furthermore, we find that centennial-to-millennial variability is stochastic in nature. We also discuss recent developments of climate models with superior resolution in typical retrieval regions of paleoclimate records, such as continental margins and coasts. 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 related to icebergs yields a quasi shutdown. Our multiscale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores....

The PMIP4 Last Glacial Maximum experiments: preliminary results and comparison with the PMIP3 simulations

“…These changes in circulation had an impact on precipitation, which was reduced globally (Bartlein et al, 2011) but increased locally, for example, in southwestern North American and in the Mediterranean region (e.g. Kirby et al, 2013;Beghin et al, 2016;Goldsmith et al, 2017;Lora et al, 2017;Lora, 2018;Löfverström and Lora, 2017;Löfverström and Liakka, 2016;Löfverström, 2020;Rehfeld et al, 2020). The interplay between temperaturedriven and circulation-driven changes in regional precipitation during the LGM represents a test of the ability of stateof-the-art models to simulate precipitation changes under future scenarios, where both thermodynamic (e.g.…”

Mathematics and Climate Change

“…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 CO 2 increase. Practically, given the present high-performance computer capacities, efficient and parallelized model codes, it is now possible to conduct simulations for 50-100 model years per day even with a multi-scale ansatz (Lohmann et al, 2020;Sein et al, 2018). Recent developments have considerably improved the computational efficiency and scalability of unstructured-mesh approaches on high-performance computing systems (Danilov et al, 2017).…”

“…Since Earth system models have to simplify the system and rely on parameterizations of unresolved processes using present data, paleoclimate records provide a unique tool to validate models for conditions which are different from our present one. Suitable model-data analyses provide therefore a proper basis to estimate and possibly reduce uncertainties of future climate change projections (Lohmann et al, 2020). Furthermore, the model scenarios in conjunction with the long-term data can be used to examine mechanisms for the statistics of regional climate extremes under different boundary conditions.…”

The archaeology of climate change: The case for cultural diversity

“…Extreme climate events, such as El Niño events, represent another potentially significant source of stochasticity; while their frequency is difficult to predict, archaeological data have been used to date and understand how farming systems in the Southern Hemisphere adapted to them (102). The frequency and scale of past climate events can now be modeled at very fine resolutions (91). The impact of an event depends on the state of the system being affected, however, which means that a cross-disciplinary approach is required in order to predict the outcome (103).…”