Research Project

Modelling climate change in the southern hemisphere

A project which sits at the heart of the Deep South Challenge is the development of the NZ Earth System Model (NZESM). An Earth System Model models our oceans, sea ice, land and atmosphere to understand how our climate will change under anthropogenic greenhouse gas emissions. 

A person sits at desk with two screens showing climate modelling

Fundamentally, the questions we are answering revolve around better understanding the Southern Ocean and Antarctica’s effects on climate and climate change and how we can better simulate it.

Key outcomes:

  • The ongoing development of the NZESM has already shown the value of modelling with a focus on the Southern Hemisphere and the oceans around New Zealand. For example, research in these projects have improved projections of marine heatwaves around New Zealand, and reduced shortwave cloud biases across the Southern Ocean.
  • Improvements made in the NZESM are being fed back to modelling teams in the Northern Hemisphere to improve the Unified Model, an atmospheric model that underpins many global climate and weather modelling efforts. 
  • Global modelling capability in New Zealand has grown, with scientific and technical expertise on climate modelling being established and supported across New Zealand.

How this research is being used:

  • The establishment of the NZESM has enabled nuanced studies on how important climate processes are changing around New Zealand. For example, how climate change may impact the frequency and strength of storms that make landfall in New Zealand.
  • Data from the NZESM have been used for research into larval connectivity modelling, and downscaled (regionally-relevant) data for understanding the meteorological conditions associated with extreme weather events. Downscaled NZESM data will be included alongside the updated climate projections for New Zealand that will be released by NIWA in 2024 for stakeholder use.

In the media:

NZESM: leaving an enduring legacy: 2022 – 2024

Budget: $600,000

The Challenge has already generated global and regional climate model projections to 2100. Hydrological simulations will follow in 2022 and these datasets will provide an unprecedented library of data.

Challenge simulations have already provided – for example – projections in changes to marine heatwaves around Aotearoa and work is already underway to examine changes in the storms impacting the country. Going forward, we will use our pre-existing model data to research upstream changes to regional climate affecting New Zealanders, for example on drought conditions. 

The Challenge has funded multiple climate modelling development studies however not all of them have been incorporated into the NZESM. This project will bring all these developments together. Some of these advances have been done in collaboration with international partners and this will provide a showcase of the world-leading model development work that the Challenge has enabled.  

Impactful climate projections need to be accompanied by impactful science communications. this project will build on the reputation gained from previous Challenge projects both to ‘advertise’ our science in near-real-time, and to leave a legacy of material which can outlive the Challenge itself.  

Climate simulations using the NZESM, the NZ RCM and the NZ Water Model: 2019 – 2022

Budget: $1,375,000

Building on the Deep South Challenge’s first phase, we were able to integrate three different computer models:

  1. Our global earth system model, the NZESM. The major improvement in this model compared to our ‘parent’ model in the UK is our high-resolution representation of the ocean in our region. This provides our model with its New Zealand “fingerprint”.
  2. A regional atmosphere climate model (which downscales the global climate model for New Zealand).
  3. A hydrological model for New Zealand – the NZ Water Model.

In our first five years, we were able to establish significant capability for climate modelling within New Zealand. We brought together climate researchers working discretely on modelling projects into a cohesive, nationwide network. Our broad team is now sharing the same modelling framework, code and model outputs, including with our international collaborators.

With the help of NeSI’s supercomputers, we have produced simulations for our climate history from 1950–2015. We are now running our first simulation of New Zealand’s future, out to 2100.

Simulating New Zealand’s changing climate: 2015 – 2019

Budget: $1,900,000

Gaps in international observations and understanding of the deep south region mean that Earth System models currently struggle to accurately represent aspects of the climate around New Zealand and the surrounding oceans, like the clean air over the Southern Ocean, or the behaviour of Antarctic sea ice.

Developing the NZESM means that New Zealand can contribute internationally to how we model processes critical to Southern Hemisphere climate and establish local expertise on how to understand and evaluate climate models and projections. Having an Earth System model “in-house” also means we can configure the model to best suit the needs of New Zealand. We are doing this, for example, by modelling the ocean at high-resolution around New Zealand to better simulate the complex ocean circulation around here.

As the NZESM is based on the UK Earth System Model, we’re also helping to develop the underlying atmospheric model known as the Unified Model, which is also used in several other climate and weather prediction modelling centres around the world.  

By strengthening our ability to understand and anticipate our future climate, we’re giving New Zealanders the best possible chance to adapt and manage risk in the years to come.


This significant endeavour is supported by an international partnership with other weather and climate modelling centres led by the UK Meteorological Office. Our global climate model is based on the UK’s version, and our international partnership is essential. We simply couldn’t do this on our own.