Author: sam prescott

Project summary from the “Modelling Antarctic Sea Ice” project led by Inga Smith and Andrew Pauling.

Check out a handy fact sheet from this project, here.

What is sea ice?

Sea ice is the layer of frozen seawater covering the ocean surface in the northern and deep southern oceans. In Antarctica, the formation of sea ice each winter and melting each summer represents one of the largest seasonal changes on Earth. The total ice cover varies by about 16 million km² between the yearly minimum and maximum. That’s approximately 60 times the size of Aotearoa New Zealand.

The trend in annual mean Antarctic sea ice area has puzzled scientists during the satellite era (1979-present), with data showing a slight increase from 1979 to 2015, and a sharp decline since.

Animation made using model output from the hist-1950 simulation from the HadGEM3-GC31-MM model submission to the Coupled Model Intercomparison Project phase 6 (CMIP6). doi:10.22033/ESGF/CMIP6.1902

Sea ice is important to global climate because it reflects sunlight, insulates the ocean, and drives cold, salty water into the deep oceans.

What is the problem?

Climate models, which are our best tools for making projections of future climate, have failed to reproduce the observed trends in Antarctic sea ice. From 1979-2015 models showed declining Antarctic sea ice area, which didn’t match the slight increase observed from satellites. There have been different explanations for the discrepancy, for example, that current climate models do not represent the changing amount of land ice in the Antarctic ice sheet.

In the real world, Antarctica is losing mass over time, and as current models do not take this into account, they exclude an important source of fresh water flowing into the Southern Ocean. It has been suggested that this missing fresh water plays an important role in sea ice trends. Additional fresh water near the ocean surface increases the density gradient between the surface and deeper water, inhibiting vertical transport of relatively warm water from the depths, which results in surface cooling and warming of the deep ocean. This surface cooling then drives sea ice growth.

Our work as part of the Deep South National Science Challenge has been to investigate the effect of this missing fresh water on Antarctic sea ice trends in a state-of-the-art climate model.

Our work

We have been investigating the effect of missing fresh water from the Antarctic ice sheet on sea ice in the HadGEM3-GC3.1 climate model, which forms the physical core of the New Zealand Earth System Model.

We have run experiments with artificially added fresh water under pre-industrial control conditions and in a scenario where atmospheric CO₂ increases by 1% each year.

In both scenarios, adding the fresh water results in greater Antarctic sea ice area relative to the simulations that exclude it, and also results in a decline in Antarctic Bottom Water formation. We have tested the effect of adding fresh water as either melting icebergs or basal melt of the ice shelves, and found that while the responses are similar, there is greater ocean warming at depth when the fresh water is added to the model as basal melt.

We have also found that adding fresh water was able to offset ocean warming due to increased atmospheric CO₂ over the continental shelf in several regions around Antarctica. The magnitude of the effect depends on the specific continental shelf geometry, the climate state, and the vertical distribution of the fresh water.

Finally, we have been contributing simulations to an international model intercomparison that aims to better understand the reasons for inter-model differences in the response to the fresh water. We have conducted several of the model simulations outlined as part of the Southern Ocean Freshwater Input from Antarctica (SOFIA) initiative, and analysis and comparison to multiple other models from around the world has shown a large inter-model spread in the Antarctic sea ice and Southern Ocean temperature responses. This highlights the importance of this model intercomparison project for quantifying both the magnitude and uncertainty in the response to Antarctic meltwater.

What are the implications for Aotearoa New Zealand?

Impacts over land in New Zealand are small in our model simulations, but there is a significant reduction in warming of the ocean surface immediately to our southeast in both historical and future warming scenarios. Analysis of the impacts of this on moisture in the atmosphere and circulation are ongoing.

Climate change adaptation is often reduced to a question of monetary-based questions. Why did we let development happen in a risky area in the first place? How much would it cost to protect communities in place now, versus thinking in a longer-term way about where communities might feel and be safest?

But what happens when the most important things to us don’t have a price tag? How do we make sure the things we value most, our connections to whenua and tipuna, are properly factored into the decisions of governments and businesses?

With so much emphasis on the fiscal costs of adapting to climate change, or not adapting, we are losing important elements that should be included in that conversation.

Check out the report from our symposium held earlier this year; see below for podcast and video links to revisit our fantastic panel sessions and speakers!

Check out updated podcast content here. All the day’s great videos here.

The Deep South Challenge is releasing the symposium report on our November 2023 conference, Adapting Aotearoa: Towards a climate resilient land and food system.

This event took place in Christchurch over two days, and saw participants across the agriculture, farming and food production sectors, meet and kōrero with academics and other professionals, to explore innovative solutions for building climate resilience and a deeper understanding of the urgency for adaptation in our agricultural practices.

We were privileged during the conference to hear from veteran journalist and climate change thinker Rod Oram, who tragically died this year (2024). Sessions from the conference were recorded, and are now available. They include Rod’s key note, and our two expert panels.

Our symposium report includes a dedication to Rod Oram.

Story by Nadine Anne Hura (via The Spinoff)

The Deep South Challenge is producing a podcast that will capture the stories of some of the researchers and communities working in our Vision Mātauranga programme. Our Kaitakawaenga Nadine has been travelling the country, listening to their kōrero. [READ on thespinoff.co.nz]

There’s a kind of awe that hits you when you understand the scale of the loss and the commitment required to heal and recover.

Yet, over and over again, people I spoke to reiterated that hope on its own isn’t the thing keeping them going. “Hope is abstract,” Shirley Simmonds of Ngāti Huri told me. She has recently made the move home to Pikitū with her whānau and is deeply attached to the shovel with which she’s she’s helped to plant the beginnings of a food forest, and also tree seedlings on land that was once – and will eventually again be – blanketed in native ngahere. “Hope needs to be activated through work,” Simmonds said. “Sovereignty is inherently practical. The solutions are within us – kei a tātou te rongoā.”

The podcast will be available in March 2024, co-hosted by Ruia Aperahama.

A mini symposium was held in Wellington 9 March 2023 to mark 10 years since New Zealand introduced dynamic adaptive pathways planning (DAPP) approaches for addressing the new climate reality and to share research and practice experience and to discuss where to next. This builds on a 10-year collaboration between Deltares, The Netherlands and the Climate Change Research Institute at Te Herenga Waka Victoria University of New Zealand, with support from the Deep South Science Challenge, the Resilience to Nature’s Challenges Science Challenge and Ministry for the Environment.

The mini-symposium was broken into four sessions—setting the context (why and how); sharing applications from New Zealand and elsewhere (what); discussing lessons learned (experience) ; advancing methods, assessment, engagement and implementation (where to).

The sixty-four participants (including fourteen online) were from research institutions and universities, local and regional government, consultant companies, crown and government agencies with experience in developing decision making under deep uncertainty (DMDU) methods, using the methods and implementing the outputs from using them. Four international researchers also attended including the developers of the DAPP and other DMDU methods from the Netherlands, a researcher and user from Boston USA applying DAPP in a cities context,  and a researcher from Denmark applying DAPP at different scales for infrastructure planning under a changing climate (the full attendee list attached).

Two presentations set the scene. One discussed the role that deep uncertainty tools can play for decision making in a changing climate reality and why we use them, and the other covered the New Zealand context and how the decision tools were socialised into New Zealand and what enabled this to happen. The report and a slide set from the mini-symposium is available here.