Global climate models (GCMs) create a virtual earth that captures our scientific understanding of how the earth’s climate works. They are run by climate modelling research centers around the world, including CSIRO and BoM in Australia.

NARCliM 1.0 projections were generated from four GCMs that form part of the CMIP3 dataset. The CMIP3 dataset was used by the IPCC in their Fourth Assessment Report (AR4), and was released in 2010.

Other CMIP datasets have been produced since CMIP3. These have informed other climate projections for NSW, such as NARCLiM 1.5.

GCMs provide projections of future climate changes based on our understanding of the Earth’s climate system, and estimations of current and future greenhouse gas emissions.

GCMs map the world into a grid of cells, usually hundreds of kilometres wide. They generate projections for those cells, which gives a good overview of climate projections at the global scale but  lacks the detail needed to clearly understand the impacts of climate change at smaller regional scales – such as NSW.

To overcome these limitations, a process called dynamical downscaling is used. NARCliM downscales data from GCMs by using high resolution regional climate models (RCMs). These regional models capture the finer details of the NSW landscape that influence its climate, such as mountain ranges and coastlines.

The NARCliM 1.0 process for dynamical downscaling uses the Weather Research and Forecasting (WRF) model, to simulate the climate at a 50 kilometre and then 10 kilometre resolution. This provides a good representation of local landscapes and coastal processes across NSW.

This approach produces the most comprehensive and reliable view of future climates for NSW and south eastern Australia. It creates future climate scenarios that are used by  scientists, governments, industries and communities to plan for future changes in climate.

Our climate is influenced by the amount of greenhouse gases in the atmosphere. Climate models make projections based on estimated future amounts of greenhouse gases in the atmosphere, known as emissions scenarios. These scenarios consider the amounts of greenhouse gases likely to be produced by natural and human activities, such as burning fossil fuels, increased energy use from population growth, and land uses such as land clearing, forestry and agriculture.

NARCliM 1.0 uses the A2 emissions scenario in the IPCC’s Special Report on Emissions Scenarios. This scenario was identified as being the most likely future scenario when the NARCliM 1.0 projections were developed, based on the global emissions trajectory and rate of population growth, economic growth and technological change.

Climate projections produced by models are the best information we have on possible future climates, but there is no way of predicting the actual future climate. Because of this, NARCLiM projections will not always match our observations of the climate.

Understanding how climate projections differ from observations helps improve the performance and accuracy of models, and our interpretation of projections.

The global and regional climate models used by NARCliM 1.0 were tested to see how well the projections matched actual observed climate data. This testing showed that downscaling and using regional climate models improved projections:

• Dynamical downscaling improved projections for rainfall, minimum and maximum temperature.
• Dynamical downscaling improved projections specific to NSW as it captured regional influences on climate, such as the mountains and coastlines.
• Using RCMs improves projections by accounting for major climate drivers in NSW, such as the El Nino–Southern Oscillation system.

Testing also showed where RCMs were less accurate (these issues are common in all RCMs):

• Rainfall tended to be overestimated.
• Maximum temperature tended to be underestimated.

The projections for these variables were improved by correcting model data with actual observed data on rainfall and maximum temperature (a process called bias correction).

NARCliM 1.0 produced a large dataset – almost 1 petabyte in size (1 million gigabytes). This dataset is recognised by the Australian Government as a dataset of national significance and is stored on Commonwealth data repositories.

To find out about these and other climate projection tools, and to access NARCliM data, see Other climate projections available for NSW. Visit the NSW Climate Data Portal website for the terms and conditions of using NARCliM data.

NARCliM is an ongoing project to provide the most comprehensive climate projections for NSW and south eastern Australia. A second set of NARCliM projections was released in 2020 (NARCliM 1.5) and a third set is in development (NARCliM 2.0).