One day my student showed me a figure that displayed strong warming in the high southern latitudes in the last interglacial experiments. It was a surprising discovery since we knew that the last interglacial Earth orbital configurations caused cooling there. We suddenly realized that our experiments were unique due to the increased global mean sea levels.
Bearing this in mind, we tried to investigate whether a sea-level rise will play an essential role in the future climate, though examining its impact with climate models remains challenging. Global mean sea-level growth lifts a sea level datum, modifies land-sea distributions, and affects relative sea levels. However, climate models cannot fully consider these processes. For example, atmosphere models generally assume that the ocean surface is flat under the atmosphere. Next, horizontal resolutions in models are not high enough to represent changes in coastal regions when sea-level uplifts range from centimeters to a few meters. Furthermore, when there is more freshwater input, some models can simulate the adjustments in ocean volume due to salinity or temperature change but still cannot simulate the increase in ocean volume due to the added freshwater volume. Finally, ocean bathymetry and land topography changes are not uniform due to isostatic responses.
To overcome the challenge, we used a deep-time paleoclimate modeling skill, changing sea levels spatially uniformly. Although this modeling remained simplified and idealized, it revealed a crucial result. A slight global mean sea-level uplift — even in tens of centimeters — generates significant climate responses, particularly at mid-high latitudes.
Our study rings the alarm bell to pay attention to the impact of sea-level rise in the global domain, not only in coastal regions. Global mean sea level has risen at an accelerated rate in recent decades, accompanied by global warming. Today it is ~20 cm higher than at the beginning of the 20th century. It is virtually certain that the sea level will continue ascending through the 21st century. Sea-level rise will likely become a non-negligible factor that influences the global climate. Given that sea-level growth adjusts large-scale atmospheric and oceanic circulations and associated synoptic systems, both coastal and inland countries are exposed to these changes and risks.
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