We have long known every tonne of carbon dioxide matters to the climate. But governments keep approving new fossil fuel projects – even as climate change worsens.

Until now, it’s been difficult to say how much damage and extra warming a specific project will do. Fossil fuel companies – and government agencies approving their projects – have often relied on what’s known as the “drop in the ocean” defence.

While backers concede a new project will add more carbon dioxide emissions to the atmosphere, they say these are tiny compared to the global tally and that it’s almost impossible to track damage attributable to the emissions of an individual project.

This defence won’t work any more. In recent years, attribution science has advanced rapidly, allowing scientists to pinpoint the role of climate change in making disasters and extreme weather more likely.

Our new open-source climate tool – the Carbon Impacts Tracer – goes one step further. It shows how much a new project will warm the planet – and how much damage it will do across eight areas, from loss of crops to heatwave deaths in Europe.

This will help make fossil fuel companies and governments approving these projects accountable for the damage they will do.

To measure the damage attributable to a single fossil fuel project, we connected the dots between emissions produced, extra warming and the damage done to people and the........

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