Exploration of natural climate variability and changes in future events using observations, proxy data and model simulations

Abstract

Human evolution and civilization are deeply interlinked with the environmental and climatic context of the planet in which they developed and continue to unfold. The principal concerns of this dissertation lie in exploring the connection and interplay between changes in Earth's climate—comprising the physical interactions and states of the atmosphere,biosphere, hydrosphere, and cryosphere—in response to two main drivers: externally forced changes, such as those caused by human activities, volcanic eruptions, and the planet’s orbital configuration; and internally generated changes arising from the natural interactions among these Earth systems. Herein I attempt to make a contribution to the current understanding of the history of the recent past as it relates to natural climatic changes by making use of my expertise as a geologist and experience in the field of paleoclimatology to meld proxy data (i.e., indirect measurements of past environmental change through archives such as ice, sediments or corals) with large datasets comprised of model simulations. Additionally, I utilize some of the data science and visualization techniques I produced to explore a state-of-the-art, high-resolution dataset developed by the Minnesota Climate Adaptation Partnership (MCAP) to generate statistical projections of extreme climate events.Chapters 1 and 2 focus on relative contributions of external forcing and internal variability to climate change during the pre-industrial last millennium (850 – 1850 CE), an era in which anthropogenic changes had not yet taken over and other phenomena were dominant. Using observational data, paleoclimate proxy records and climate model simulations, we assess the evidence for natural, internally generated climate oscillations on multidecadal timescales (~50-80 years) and evaluate whether external forcing mechanisms, principally volcanic eruptions, are to blame for apparent oscillatory behavior, with a focus on the North Atlantic Ocean and surrounding land areas. Chapter 3 focuses on the future, aiming to characterize how extreme precipitation events—among the most impactful weather phenomena in Minnesota, particularly in relation to flooding and infrastructure design—may change in response to both natural and human-induced climate change.