Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures

Abstract

While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty, the Intergovernmental Panel on Climate Change (IPCC) reported that sea-level rise from the 1950s levels would likely be within 0.61-1.10 m if warming exceeds 4 C by 2100. The IPCC acknowledged greater sea-level increases were possible through mechanisms not fully incorporated in models used in the assessment. In this perspective, we discuss challenges faced in projecting sea-level change and discuss why the IPCC's sea-level range for 2100 under strong warming is focused at the low end of possible outcomes. We argue outcomes above this range are far more probable than below it and discuss how decision makers may benefit from reframing IPCC's terminology to avoid unintentionally masking worst-case scenarios.

Reducing Uncertainty in 21st Century Sea-Level Predictions and Beyond

“…Sea level rise will continue in the 21st Century, and well beyond it (Siegert et al, 2020). Whether this rise will be contained to <1 m, or be much higher, will depend on whether 1) we can curtail greenhouse gas emissions to "net zero" by mid-Century, thus stalling the atmospheric CO 2 concentrationand then bringing it downso that global warming can be restricted to the 1.5 °C target (relative to the pre-industrial level), and 2) the polar ice sheets will react more rapidly than observed to date, in ways we know they can and have in the past (IPCC, 2019).…”

“…While such experiments are useful in understanding processes that may be responsible for mass loss, and much progress has been made in ice-sheet modelling over the last few decades, there still exists a number of limitations to the models that preclude accurate 21st Century predictions. Siegert et al (2020) point to six issues that urgently need to be resolved as they would help reduce uncertainties in predictions: 1) mapping of subglacial topography, as model outputs are only as good as the inputs, and the landscapes beneath the Greenland and Antarctic ice sheets are far less well resolved than the potential resolution of the models; 2) collecting more ocean data at the ice-sheet marine margins to better comprehend the supply of heat to the most vulnerable sections of the ice sheet; 3) acquiring geophysical information from the ice-bed interface, as the material properties of the bed dictate how rapid the ice can flow to the ocean; 4) improving the coupling between ice sheet, ocean and atmospheric models, to allow feedbacks and process interplays to be factored into predictions; 5) undertaking laboratory investigations of ice fracturing, as it can lead to sudden changes in ice-sheet conditionssuch by the disintegration of floating ice shelves; and 6) enhancing our knowledge of past changes in order to "train" models.…”

“…The amount that is built in and the level to which can mitigate further increases are key issues for the 21st Century, including in the near term of the next 2 decades given persistently high emissions levels. This will determine whether and how we can inhabit today's coastal regions for the rest of this century and beyond (Siegert et al, 2020;Aschwanden et al, 2021).…”

A Roadmap for Policy-Relevant Sea-Level Rise Research in the United Arab Emirates

“…First, scientific understanding of sea-level rise is advancing at a rapid pace. Projections of future sea-level rise have increased substantially (e.g., Siegert et al, 2020;Slater et al, 2021) and these projections will continue to change as scientific understanding rapidly advances. The planet as a physical system is more sensitive than previously thought (Lenton et al, 2019).…”

Spatio-temporal changes of precipitation in the Hanjiang River Basin under climate change

“…The fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC) pointed out that the significant warming of the global climate system in the past 100 years has had extensive and profound impacts on human society and natural ecosystems (Beck and Oomen 2021;Cavanagh et al 2021;Djalante 2019;Siegert et al 2020). A healthy and stable climate and environmental system is essential to the sustainable development of human society (Lai et al 2019;Lucas 2021;Shi et al 2021;Wilhere 2021).…”