Antarctic landcape from the air

Antarctic ice sheets cover about 98% of the Antarctic continent. Photo: Bella Zeldis

Case Study: ASP researchers contribute the IPCC Assessment Report 6

2 August 2021

The 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR6) was released to the public on the 10th of August, but for the last 6 years ASP researchers, Nick Golledge and James Renwick, have been assessing the plethora of international scientific literature and writing the Report as New Zealand’s representatives on the international Working Group 1 team. James is the co-ordinating lead author of Chapter 10 assessing regional climates, and his own research on Antarctic sea-ice and its consequences for global climate makes an important contribution. Nick is a lead author of Chapter 9 which covers ocean, cryosphere and sea-level change. The ASP modelling of the Antarctic and Greenland ice sheet contribution to future sea-level rise, has also made a major contribution to the report.

The ice sheet model developed at Victoria University of Wellington, and used by the ASP National Modelling Hub members, is one of the models chosen by the Ice Sheet Model Intercomparison Project Experiment 6, whose job is to estimate the polar ice sheet contribution in the latest sea-level projections in the IPCC report. Nick and early career ASP researcher, Dan Lowry, have co-authored 10 scientific papers with their international team in time for inclusion in the IPCC Report. Two high profile publications in Nature that were highly influential in the assessment were co-funded by the ASP; “Projected Land Ice Contributions to 21st Century Sea-Level Rise”, was published in May this year. The paper demonstrates that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. However, land ice could contribute up to 75cm by 2100 (of the 1.5 m total) of sea-level rise alone, without emissions reductions. Published in 2019, but cited in the AR6 report, a paper named “Global Environmental Consequences of Twenty-First-Century Ice-Sheet Melt” led by the co-leaders of the ASP National Modelling Hub, showed that fresh meltwater discharged to the ocean could provide a positive feedback enhancing the rate and magnitude of polar ice sheet melt.

Sea ice in the Ross Sea

Sea ice in the Ross Sea. Photo: Brian McKerrow

The IPCC AR6 further strengthens the scientific evidence and consensus that the consequences of climate change are already being felt, and will continue to be felt for decades to come. It reinforces the urgency to mitigate in order to avoid the severest impacts. However, even if the world achieves the target of the Paris Agreement, we are now committed to some serious impacts that can’t be avoided, and the report implies that adaptation will be paramount.

This is certainly the case with rising seas, that will impact at least 800 million people by the end of the century. Although the projected “likely” range (17th-84th percentile) for global sea-level rise by 2100 hasn’t changed significantly from the previous (5th) assessment report (0.44-1.01 m for all emissions scenarios) the new report does state, that “mean sea level rise above the likely range – approaching 2m by 2100 and 5m by 2150 under a very high GHG emissions scenario (SSP5-8.5) cannot be ruled out, due to deep uncertainty in ice sheet processes”. This will continue to challenge NZ local and central government agencies charged with the governance and management of infrastructure, assets and communities living on the coast.

The elephant in the room continues to be our ongoing lack of understanding of how Antarctica’s ice sheets will respond. One of the highest priorities for the international research community, including the ASP, is to quantify the rate of future mass loss of Antarctic ice, and to determine if or when a tipping point will be crossed, that will cause multi-generational ice loss and multi- metre sea-level rise.

This ASP-led research, while making a significant contribution to the IPCC AR6 is also being taken up directly through the MBIE Endeavour-funded NZ SeaRise Programme, which is poised to release its new location specific sea-level projections for the entire New Zealand coastline. These projections that account for vertical land movements and the latest estimates and uncertainties on Antarctica’s contribution, will help NZ stakeholders and decision-makers adapt to the impacts in an effective and timely manner. The release of NZSeaRise projections is being co-ordinated with MfE and timed with the release of the AR6 Working Group 2 Report in early 2022.

This Case Study was submitted to MBIE as part of the ASP annual reporting for the 2020-2021 year. It is an example of world class NZ-led, policy facing research, achieved through close collaboration between two MBIE investments that is having both NZ and global impact.