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  • Climate affects our lives, and it will continue to affect our future. But how do we know what might change over time? Scientists often use models to represent and test ideas and processes. A global climate model (GCM) is a model of how the Earth’s atmosphere, oceans, land surfaces and sea ice interact to affect the climate.

    Each of these Earth systems is complicated on its own, but when combined, it gets very complex!

    Rights: Le Treut, H., R. Somerville, U. Cubasch, Y. Ding, C. Mauritzen, A. Mokssit, T. Peterson and M. Prather, 2007: Historical Overview of Climate Change. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

    Interacting cycles affect the climate

    The climate system is extremely complicated. Ideally, climate models simulate as many of the physical, chemical and biological influences as possible.

    Climate models have two main functions. The first is to accurately represent the current climate and the interactions between Earth’s land, water and atmospheric systems. The second function is to help us understand what might happen with future climates. The models allow us to experiment with different features – like warming atmospheric temperatures or oceans that are more acidic – to see what impacts the change could have on the climate. These ‘What if?’ scenarios help governments, cities and towns, businesses, land users and individuals plan for the future.

    Models in science

    In science, a model is a representation of an idea, an object, a process or a system that is used to describe and explain phenomena. By making a model (a smaller working version of something), scientists can examine individual components and see how they respond to change.

    Models are often used to explain complex data. There may be more than one model to explain or predict what might happen in particular circumstances. Often, scientists evaluate the ‘correctness’ of a model. In the process, the model might be modified – or even rejected.

    Nature of science

    Scientists use models as a way of representing phenomena. These days, models are often mathematical and run on computers rather than being visual representations.

    Building a climate model

    To understand how global circulation climate models are built, think Minecraft. The Minecraft world is divided into blocks that are used to create 3D models. Climate models divide the world into 3D blocks called grid cells. Each cell has information about whether it is covered by water or land and the land use – for example, farm, mountain or city. Each cell also uses physical and chemical laws to simulate the movement of air, water and energy. The mathematical equations are turned into computer code. Additional coding allows the different grid cells to interact. To complicate things even further, climate happens over a period of years, so the models run on hourly, daily or weekly timescales.

    Rights: Image courtesy of Geophysical Fluid Dynamics Laboratory, National Oceanic and Atmospheric Administration, USA

    Grid cells

    Three- dimensional climate models divide the Earth into grid cells.

    Increased computer power means the models are continually improving to run at higher spatial and temporal resolutions. Smaller grid cells and shorter time steps allow the models to become more accurate at regional or local scales. Climate models may start off like Minecraft and have a few things in common with The Sims video game series – but to be meaningful, they require petabytes (1015 bytes) of data storage!

    Determining accuracy

    Regardless of the amount of data a model uses, it still needs to accurately simulate the Earth’s complicated and interacting systems. To validate the model or check its accuracy, scientists use observational data. The data comes from current climate records and historical records like ice and sediment cores. If a model produces similar results to what actually happened in the past, it is considered trustworthy.

    Rights: Intergovernmental Panel on Climate Change, 2007

    Improved resolution in climate models

    As computer processing becomes more powerful, climate models can run at higher resolution and provide more detailed information.

    In addition, the models undergo peer review. Research groups around the world compare results between models. If necessary, revisions are made to the equations or coding. Research shows climate model software has fewer bugs (errors) than leading commercial software.

    Climate models are not perfect. It is not possible to fit the complexity of the Earth into a model. However, none of the GCMs can explain the Earth’s recent warming without the influence of rising greenhouse gas concentrations. This finding adds to the cumulative evidence that our current experiences of climate change are associated with human activity.

    Climate models – the New Zealand experience

    The National Institute of Water and Atmospheric (NIWA) developed regional-scale projections (forecasts) of climate trends and variability to the year 2100. NIWA scientists selected the six best-performing general circulation models for New Zealand, based on how they fit with observed and historical data. They improved the spatial resolution to grid cells of about 5 km using information from NIWA’s Regional Climate Model.

    Using this information, the Climate Changes, Impacts and Implications for New Zealand (CCII) project developed case studies about potential impacts of climate change on alpine, upland, lowlands, coastal and marine systems. The website Our Future Climate New Zealand uses the regional climate model output to explore the spatial and temporal variability of climate projections for several New Zealand locations.

    Related Hub resources

    Earth system, What is the Earth system? and The ocean and Earth’s systems and cycles provide more information on the complex interactions that occur on our planet. The Argo project collects oceanic data used in GCMs.

    Read how scientists use direct observation to validate sea ice thickness and atmospheric measurements in Antarctica.

    Watch this video to find out more about the Argo project and New Zealand's involvement in it.

    MethaneSAT is Aotearoa New Zealand’s first government-funded space mission. Find out how it is helping inform global emission models.

    Dr Mike Williams is the director of the Deep South Science Challenge leadership team. Read about the Deep South Challenge objectives in New Zealand's National Science Challenges.

    Useful links

    Read about the Deep South Science Challenge and the work to build a New Zealand Earth Systems Model in this New Zealand Geographic article: New Zealand's Next Top Model.

    This Columbia University blog post is a beginner’s guide to climate models.

    Watch this TEDx talk: Should we trust climate models?

    The Coupled Model Intercomparison Project enables a diverse community of scientists to analyse GCMs in a systematic fashion to facilitate model improvement.

    The interactive website Our Future Climate New Zealand has been designed to provide the ability to look at a number of climate change projections for New Zealand.

    Find out more about The CCII (Climate Changes, Impacts & Implications) project that ran from 2012 to 2016 on the NIWA website here, included are a range of reports.


    Thin Ice – The Inside Story of Climate Science, a David Sington/Simon Lamb film, looks at what’s really happening with global warming by filming scientists at work in the Arctic, the Antarctic and around the world. It gives a 56-minute view of the range of human activity and scientific work being undertaken to understand the world’s changing climate. The result is a unique exploration of the science behind global warming and an intimate portrait of a global community of researchers racing to understand our planet’s changing climate.

    The Science Learning Hub has produced a series of articles using short video resources produced by the Thin Ice team. The film itself is available by emailing It is recommended viewing to give students context for the Hub’s articles and the videos they contain. The link for streaming is available free of charge. The DVD is also available to New Zealand schools for $20 to cover costs.

    Learn more at

      Published 12 April 2017, Updated 11 February 2022 Referencing Hub articles
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