The impacts of reduced ice sheets, vegetation, and elevated CO2 on future Arctic climates

Abstract

This study investigates the climatic response of the Arctic to key factors that could shape future climate scenarios: significantly reduced ice sheets, changes in vegetation, and elevated CO2 levels. Using the EC-Earth3.3 Earth system model (ESM), we explore the effects of these forcings under conditions reminiscent of the mid-Pliocene, a key reference for potential future warm climates. Our results reveal that the Arctic climate response varies significantly with different CO2 levels, primarily due to feedbacks involving sea ice and surface albedo. The effects of the reduced ice sheet are, in a pre-industrial CO2 environment (280 ppm), an Arctic warming of 2.4°C. This is driven by substantial sea ice loss in the Barents Sea, which reduces surface albedo. Surprisingly, at 400 ppm CO2, Arctic warming incurred from the ice sheet reduction is lower than expected, at 1.9°C, because sea ice loss is less pronounced compared to pre-industrial conditions, leading to smaller albedo changes. At 560 ppm, the warming is more substantial (2.9°C) but still less than expected, largely due to the already reduced sea-ice extent at this high CO2 level. Vegetation changes further modulate Arctic climate dynamics. At 400 ppm CO2, the expansion of needleleaf evergreen trees decreases surface albedo, adding an additional 0.5°C of warming. However, at 560 ppm CO2, the warming effect of vegetation growth was muted (0.3°C) due to the development of a more diverse canopy with brighter deciduous species, which mitigates the albedo-driven warming. Our findings underscore the complex interplay between CO2 levels, sea ice, and vegetation in determining in Arctic climate dynamics. They highlight that the importance of maintaining CO2 levels at or below 400 ppm to moderate Arctic warming effectively. This study emphasizes the value of integrating paleoclimate insights into future climate projections and underscores the need for a more detailed examination of feedback mechanisms to enhance the robustness of climate models.

Keywords

• Arctic climate change
• paleoclimate modeling
• sea ice
• vegetation feedbacks