CSIRO is today expected to announce up to 350 people will lose their jobs – just days after the Australian government boosted funding to the national science agency by A$387 million.Our scientific colleagues have told us roughly a third of CSIRO’s climate modellers are expected to lose their jobs – five out of 15 scientists. These cuts come on the back of decades of slow but steady reductions in funding in the same area. This would threaten Australia’s ability to do its own climate modelling at a time when the United States has drastically cut its climate science program.The cuts pose a direct threat to Australia’s climate model, known as ACCESS (Australian Community Climate and Earth System Simulator). It’s the only global climate model developed in the southern hemisphere.If ACCESS funding is slashed, Australia will have less ability to model how climate change will affect us. That means less ability to forecast how threats such as sea-level rise will play out and plan how we adapt. What’s at stake?Our scientific colleagues have told us these plans include cutting roughly a third of the approximately 15 scientists who look after ACCESS – a foundational climate program that few people know about. A climate model is a computer simulation of Earth’s climate system. It might sound abstract, but its findings are extremely important to all of us. Global climate models such as ACCESS began as scientific tools to study Earth’s changing climate. But they have become much more than that. These sophisticated models have become vital for policymakers who have to take critical decisions at global, national and local levels.The landmark 2015 Paris Agreement – in which the world agreed to hold global warming as close to 1.5°C as possible – was built in large part on predictions made by climate models, one of which bears the “Made in Australia” trademark – the ACCESS model. CSIRO has developed and run this climate model for several decades, even as budgets shrank. Ten years ago, major funding cuts significantly reduced Australia’s global climate capabilities until they were globally marginal. These capabilities had taken many decades to build and grow. On its website, CSIRO emphasises the importance of ACCESS, stating: At CSIRO, we use ACCESS to contribute to major international climate modelling and prediction projects.Now the likely loss of these scientists means we face the threat of losing the capability of having an Australian global climate model altogether, alongside our credibility in international climate modelling efforts.What’s climate modelling for?While we experience yet another cut to climate modelling, climate models elsewhere, especially in the European Union, are being upgraded to answer ever more complex and detailed questions. Questions that we need to answer here too. They include:how do we ensure our climate adaptation strategies are sound and will not further fuel the cost-of-living crisis? how will the changing weather affect our ability to reach net zero in Australia, the Indo-Pacific region and globally?how might sea-level rise be locally distributed and interact with changing local weather conditions to amplify flooding?Without ACCESS, we are at grave risk of not being able to answer these questions in Australia. This threat to our sovereign capability seems short-sighted. Australia has long collaborated with overseas scientists and agencies and used their data. But this is becoming less certain. In the US, cuts to climate research threaten climate modelling efforts there. Geopolitical tensions and future election outcomes in other nations could mean decreased willingness to share scientific data, including information about future climates.An Australian climate model?ACCESS is the only global climate model developed in the southern hemisphere. Our soils, landscapes and vegetation are unique. So too is the weather and climate that shape them. Crucially, these factors are very different to those in the northern hemisphere. Models built in Europe, such as at the UK Meteorological Office, naturally focus on processes that affect European climates. The same is true for other regions and nations. So who, if not us, is going to build and sustain a global model with Australia squarely in mind?International collaboration at riskBeyond our own shores, Australia has been an active member of the international community collaborating to provide projections of our future climate since the 1990s. In the past, we were recognised as a scientific powerhouse. This reputation enhanced our credibility at negotiating tables all over the world, none more so than at the annual United Nations climate talks, the next edition of which will be co-chaired by Australia.Losing the ability to contribute our global model to future UN-led climate assessments by the Intergovernmental Panel on Climate Change will undoubtedly diminish our standing as a nation well beyond the climate science community. But make no mistake, it will affect that community, too. We speak to the next generation of climate scientists every day when working with students and research fellows. Worryingly, more and more of them ask whether there is a future for them here. The answer used to be obvious. It no longer is. The threat of brain drain will become a reality.All this makes today an important day for Australia. Are we going to follow those nations that are decreasing the funding for climate science? Or will we join those investing in developing the scientific capabilities that allows their citizens and governments to plan with confidence?We still have a choice. CSIRO’s media team has been contacted for comment.Christian Jakob receives funding from the Australian Research Council. CSIRO is a partner in the ARC Centre of Excellence for the Weather of the 21st Century.Andy Hogg receives funding from the Australian Research Council. He is Director of ACCESS-NRI, which receives funding from the National Collaborative Infrastructure Strategy (NCRIS) in the Department of Education. Sarah Perkins-Kirkpatrick receives funding from The Australian Research Council and the Minderoo Foundation; and is the current president of the Australian Meteorological and Oceanographic Society. She previously worked at CSIRO as a climate scientist.