Author: sam prescott

Fresh water’s impact on Antarctic sea ice

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.

Revisiting Ko Papa Ko Rangi

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.

Intergenerational Intimacies: a whakapapa conceptualisation of kai (webinar)

A whakapapa conceptualisation of kai

Hana Burgess & Haylee Koroi in conversation with Naomi Simmonds
Co-hosted by Toi Tangata & Te Kōmata o te Tonga, The Deep South National Science Challenge

In this webinar, we bring to the fore a whakapapa conceptualisation of kai, one that centers whanaungatanga – being in good relation. When we talk about kai, we are talking about the food we eat, but through whakapapa, the concept ‘kai’ evokes the many layers of whanaungatanga that constitute kai – whanaungatanga ki ngā atua, ki te taiao, ki te tangata, ki a koe anō. Here, the concept of whanaungatanga – being in good relation, is brought to the centre.

In centering whanaungatanga, we recognise that for our generation being in good relation with kai requires seeing through, and beyond, settler colonialism. Therefore, this kōrero will also seek to expose some of the ways that settler colonialism, and the imposition of hierarchies of race, class and gender, continue to damage and disrupt our relationships with kai.

Through whakapapa, kai is a call for intergenerational vision. It is a call for community and solidarity. It is an acknowledgement that kai is not separate from te taiao, kai is te taiao. Being in good relation with kai is acknowledging the expansive ways that kai nourishes us.

In conversation with Naomi Simmonds from Te Kōmata o te Tonga, The Deep South National Science Challenge, this webinar invites us to deeply consider our relationships with kai, to immerse ourselves in the intergenerational intimacies that kai evokes.

Hana and Haylee’s paper Intergenerational Intimacies is also available for download.

Impact of a changing climate on our energy system

Image of the Pukaki canel
Image of the Pukaki canel

Decarbonising our economy is leading to electrification of both transport and industry, resulting in a doubling of electricity demand in New Zealand in the next 30 years (BCG 2022). Significant new electricity generation will primarily consist of new wind and solar farms, as these have very low emissions and are now the cheapest new forms of electricity generation. The proportion of renewable electricity in our system will increase to close to 100% by the mid-2030s (BCG 2022). Increasing intermittency of supply from variable renewables will mean that when the wind stops blowing and the sun stops shining, we need either storage (e.g. hydro storage, batteries, pumped hydro) or firm dispatchable power (e.g. geothermal) to continue reliable supply. Wind generation is projected to make up ~30% of our electricity mix by 2050 (BCG 2022), and the importance of hydro storage dams will increase, as water can be held back behind the dams when wind and solar supplies are strong, and then used to generate electricity when there is no wind or solar generation available.

However, climate change is going to impact the arrival of these important renewable generation “fuels” as well, and until now this has not been factored into energy models looking out to mid-century. 90 years of historical wind and hydro inflow records are currently used to estimate how much wind and water we are likely to have in 2050, and this assumption is flawed. Climate change impacts on wind and water need to be included in energy planning.

Projected changes to wind and water

This research investigated climate change impacts on the wind and water needed for the energy transition. Projections of wind and water, sourced from Global Climate Models (GCM) and downscaled to local level (Collins 2020, Collins, Montgomery and Zammit) by NIWA scientists (Dr Christian Zammit and Dr Richard Turner), were combined with high resolution electricity system modelling, to explore how changes to wind and water will impact our ability to generate enough renewable electricity to support New Zealand’s decarbonisation goals.

Datasets and guidance from this research allow energy planners to incorporate information they haven’t previously had access to.

Local scale projections show significant changes to both lake inflows and wind speeds by mid-century. On an annual basis, South Island hydro lakes are expected to get wetter and North Island hydro drier over time. Seasonally, the biggest changes between now and 2050 are projected to be 8% higher winter inflows in the big South Island snow-fed catchments (under a middle of the road emission scenario), and 8% lower summer lake inflows in the North Island hydro catchments (see figure 1).

It is projected to get slightly windier everywhere, on an annual basis. Seasonally, winds are expected to get weaker in summer and autumn, and stronger in winter, by mid-century under a mid-range emissions scenario (see figure 1).

Figure 1: Projected % changes to weekly hydro inflows (left) and wind speeds (right) in electricity model regions between 2022 and 2050. Regions/catchments to the left of the black line are in the South Island, regions/catchments to the right of the black line are in the North Island.

Floods are expected to get larger over most of the South Island, and dry periods drier in the biggest hydro catchments. In the North Island, both floods and dry periods are expected to get drier over time. Wind speeds are generally expected to get higher, with both low wind speeds and high wind speeds increasing over time (see figure 2).

Figure 2: Projected % changes to the a) magnitude of flood peaks (change to 95th%ile inflows) and drought depth (change to 5th%ile inflows), and b) to the magnitude of high wind speeds (change to 95th%ile wind speed) and low wind speeds (change to 5th%ile wind speed) for various New Zealand regions, between 2022 and 2050.

Electricity system modelling

The New Zealand electricity system is generally modelled out to 2050 using a long history of past hydro lake inflows and wind speeds. For this research, projections of future water and wind were put through an industry sourced electricity system model (on licence from Meridian Energy Ltd). Three scenarios were modelled:

  1. Using historical hydro inflows and wind records.
  2. Using RCP 4.5, mid-range, emissions scenarios projections of wind and water.
  3. Using RCP 8.5, high-range, emissions scenarios projections of wind and water.

b) and c) (above) are hereafter referred to as the “climate change scenarios”. All other model assumptions were kept the same (generation plant, transmission grid, and demand side climate change impacts such as electrification of transport and industry, changes to heating and ventilation load, doubling of demand and large build programme of new generation).

Results showed that increases to wind and water under the climate change scenarios led to a slightly reduced need for new generation capacity (and subsequent new build capital costs). Although this was a small percentage change (2-4% reduction in costs), this is significant considering that $42 billion is expected to be spent by 2030 on new infrastructure in the energy system (BCG 2022). This equates to about one less wind (or solar) farm under a mid-range emissions scenario, and four less farms under a high range emissions scenario.

As flood peaks get bigger under the climate change scenarios, more hydro water is spilt down spillways without being used for generation, and spill is more likely to occur through much of the year, instead of being mostly confined to summer (as it is now). Hydro generation increases under these scenarios, as more water is expected overall. Less range of hydro storage is used (as incoming water shifts out of summer and into winter, when it is needed), especially in late winter. 

The seasonal and geographical changes to wind and water led to less system shortages in the climate change scenarios (and therefore less demand response and battery use).

Figure 3: Changes in modelled electricity system by 2050, relative to using historical wind and water.

Future work

Climate change is already having a significant and quantifiable impact on the world around us, and now that reliable projections are available, it is important that this information is included in planning for significant infrastructure development in New Zealand. There is significant variability around projections of the future of the New Zealand electricity system, with many moving parts, but to provide more certainty to infrastructure developers and government agencies, information from this research should be included in New Zealand energy planning.

References

Ackerley, D.; Dean, S.; Sood, A.; Mullan, A.B. 2012 Regional climate modelling in New Zealand: Comparison to gridded and satellite observations. Weather Clim. 2012, 32, 3–22.

Boston Consulting Group 2022: The Future is Electric. A Decarbonisation Roadmap for New Zealand’s Electricity Sector. 206pp. https://web-assets.bcg.com/b3/79/19665b7f40c8ba52d5b372cf7e6c/the-future-is-electric-full-report-october-2022.pdf

Collins, Daniel B. G. 2020: New Zealand River Hydrology under late 21st Century Climate Change. Water 2020, 12, 2175; doi:10.3390/w12082175.

Collins, D., Montgomery, K. & Zammit, c. 2018 Hydrological projections for New Zealand rivers under climate change – Prepared for Ministry for the Environment, June 2018, 108pp. https://environment.govt.nz/assets/Publications/Files/Hydrological-projections-report-final.pdf

Other resources

A printable pdf version of this project summary can be downloaded below.

A policy relevant summary can be found here.

Watch Jen present her research here.

Symposium report: Adapting Aotearoa

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.

Five climate lessons from Māori communities (that are guaranteed not to depress you)

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 Decade of Dynamic Adaptive Decision-making tools in New Zealand

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.