Earth’s two large ice sheets, in Antarctica and Greenland, are currently deteriorating and will continue to deteriorate even under the most optimistic greenhouse-gas emissions scenarios. They are a major contributor to sea-level rise and the subsequent damage to natural and human systems. We cannot stop sea-level rise, but we may be able to slow it while humanity does the necessary shift away from carbon-based energy systems.
Over the last four decades, scientific research on ice-sheet deterioration and sea-level rise has been focused on two essential questions:
1. What physical processes cause ice-mass loss that contributes either directly or indirectly to sea-level rise?
2. How is climate change affecting these processes?
Significant progress has been made on these scientifically (and logistically) challenging questions. Most notably, research has identified the physical instability processes that can accelerate ice-sheet mass loss leading to sea-level rise, even under steady or improving climate, as well as “hot spots” where instability may be happening now, e.g., the Thwaites Glacier in the Amundsen Sea sector of Antarctica.
Answers to the above questions have recently raised three further questions that are argued to be essential in driving research over the next two decades. These questions are:
3. What natural processes might limit ice-sheet deterioration?
4. Are there human interventions that could enhance these natural processes, thereby slowing sea-level rise?
5. What is our window of opportunity for implementing these interventions?
If there are technically feasible and socially acceptable interventions, they could greatly reduce the harm from sea-level rise. They would in no way reduce the imperative need to reduce fossil fuel consumption and all the other harms it causes (climate change, ocean acidification, storm intensification, droughts, floods, heat waves, wildfire, permafrost loss, etc.).
This document lays out a research agenda for answering these questions over the next decade, along with a consultation process for ensuring the transparency of the research and its relevance to future decisions about pursuing such interventions. The present document does not advocate for intervention; rather, it advocates for research into whether any interventions may be viable. It describes a pathway to identify possible interventions and the window of opportunity for pursuing them, assuming that the more quickly we know the research answers, the greater the opportunities will be, should any be viable. That window will also depend on the world’s ability to reduce greenhouse gas emissions, thereby reducing pressure on glaciers. However, given the long residence timescale of carbon dioxide in the atmosphere and emissions already made, even the most optimistic reductions of future greenhouse gas emission, in the absence of either carbon dioxide removal or solar geoengineering used at sufficient scale to significantly reduce radiative forcing, will not prevent ice-sheet melt and attendant sea level rise.
Our proposal recognizes the additional pressures from thermal expansion of the oceans; ablation of smaller glaciers, ice caps, and the margins of the Greenland Ice Sheet; destabilization of Antarctica, with surface meltwater damaging the structural integrity of buttressing ice shelves. The proposed research also recognizes that destabilization of the Amundsen Sea sector of Antarctica is primarily driven by submarine, rather than atmospheric, melting; that the submarine melting has large natural inter-annual variability; and that glaciers in the Amundsen sector, including Thwaites and Pine Island may have already crossed a tipping point into unstable dynamic collapse, with self-reinforcing feedbacks involving grounding line retreat, ice flux, ocean-cavity volume, and basal melt rate, accelerating mass loss.
Onset of ice-sheet instability cannot be ruled out even under extremely aggressive emissions reductions
Ice-sheet instability is a function of the time-integrated effects of ocean and atmospheric warming. Time-integrated effects of warming on the Antarctic and Greenland ice sheets will thus persist regardless of how aggressively emissions are reduced in the future. This means that part of the ice-sheet-driven sea-level rise is essentially independent of future emissions scenarios. Therefore, research on glacial interventions may be applicable under the most optimistic future decarbonization pathways. All research supports the intuitive logic that high, business-as-usual (e.g., the Representative Carbon Pathway, referred to as RCP8.5, that results in 8.5 W m-2 radiative forcing by 2100) greenhouse-gas emissions will accelerate Antarctic and Greenland ice sheet–driven sea-level rise. It is not clear, however, whether achieving the low-emissions scenarios or the international reduction pledges set out in the 2015 Paris Agreement and its updates would be sufficient to prevent or slow ice-sheet collapse driven by cumulative emissions to date. If the tipping point into dynamic collapse for parts of the Amundsen Sea sector of the West Antarctic Ice Sheet will soon be, or has already been, crossed, then future emissions scenarios will have little effect on preserving the ice sheet. Therefore, society may benefit from direct engineering interventions even in low-emissions scenarios.
All research supports the intuitive logic that high, business-as-usual (e.g., the Representative Carbon Pathway, referred to as RCP8.5, that results in 8.5 W m-2 radiative forcing by 2100) greenhouse-gas emissions will accelerate Antarctic and Greenland ice sheet driven sea-level rise. It is not clear, however, whether achieving the low-emissions scenarios or the international reduction pledges set out in the 2015 Paris Agreement and its updates would be sufficient to prevent or slow ice-sheet collapse driven by cumulative emissions to date. If the tipping point into dynamic collapse for parts of the Amundsen Sea sector of the West Antarctic Ice Sheet will soon be, or has already been, crossed, then future emissions scenarios will have little effect on preserving the ice sheet. Therefore, society may benefit from direct engineering interventions even in low-emissions scenarios.
The research agenda envisioned here recognizes that implementing an ice-sheet preservation intervention will be one of the more fateful decisions that climate change has forced upon world society. As a result, the vision outlined here reflects a new ethos that goes beyond the motivations that have guided glaciological research for decades. This ethos prioritizes a focus on the impacts of glaciological processes on the well-being of global societies, and it calls for robust participation of sociologists, humanists, ecologists, community leaders, scientific and engineering governing bodies, international treaty organizations, and other relevant stakeholders in guiding the research so that it provides the answers needed for informed decisions about interventions.