On the Future of Arctic Sea Ice - Projections, Dynamics, and Human Impacts

Abstract

<p>Arctic sea ice (ASI) is a critical component of the Earth’s climate system, serving as both a regulator of energy exchange and a sensitive indicator of climate change. Over recent decades, ASI has experienced a dramatic decline in both extent and thickness, driven by rising global temperatures and amplified by Arctic feedback mechanisms. This decline is a key driver of Arctic amplification, a phenomenon where the Arctic region warms nearly four times faster than the global average. The consequences of this rapid warming extend beyond the Arctic, affecting local ecosystems, global climate systems, and human activities. Despite significant advances in observational tools and climate modeling, projecting the future of ASI remains challenging due to the complex interplay of feedback mechanisms and increasing variability in the ice cover. Even the most advanced models in the latest phase of the Coupled Model Intercomparison Project (CMIP6) show significant discrepancies in predicting the timing and temperature threshold of complete ASI loss, highlighting the challenges of accurately representing ASI dynamics. <p>The scope of this thesis is to investigate the future of ASI through three interconnected studies. The first study develops an observation-based projection of the September ASI area — the time of year when ASI extent reaches its annual minimum — revealing an accelerated decline in response to rising global mean temperatures. Our results narrow the spread found in CMIP6 model predictions, placing the complete loss of September ASI cover (area below 1 million km²) between 1.5°C and 2.2°C above pre-industrial levels. The second study investigates the variability in year-to-year fluctuations of the September ASI area across models participating in CMIP6, under varying levels of greenhouse gas emissions. It identifies a consistent pattern of increasing variability as ASI nears complete loss, with the most pronounced effects observed in the Central Arctic. These findings suggest a loss of stability in this historically stable region as ASI decline progresses, highlighting a shift in Arctic dynamics. Lastly, the third study explores the effects of black carbon emissions from Arctic shipping, an activity that is growing rapidly in response to the decline in ASI cover. It compares the impacts of two major maritime routes — the Northern Sea Route and the Transpolar Sea Route — on ASI, revealing regionally distinct changes in ASI reflectivity between the two pathways and underscoring the importance of careful planning for anthropogenic activities in the region.