From past temperature change to future sea level rise, climate science is full of conflicting numbers. Here’s our guide to the ones you can and can’t trust

When ice melts, sea level rises – but how much, and how fast? Paul Nicklen/National Geographic Creative

TWELVE years to save the planet. Warming of 3°C, or perhaps 5°C if we don’t take drastic action now. Sea level rise of 0.3 metres by 2100 – or is it 3 metres?

Just about every article you’ll read about climate change is full of numbers, starting with 1.5°C, the number that we are told represents the maximum temperature rise we can allow and still avoid the worst effects of global warming.

Except it isn’t – and that is just the beginning of the confusion. No two numbers from climate change studies ever seem to agree. Even climate scientists are often baffled by the figures other researchers come up with.

Climate change deniers seize on the uncertainty as evidence that the underlying science is wrong. It’s not. It is just complex, as messy, real-world science is. The biggest uncertainty by far is us, namely what exactly we do over the next century. And the uncertainty cuts both ways: we could be underestimating how fast the world will warm and what the effects will be.

So what numbers can and can’t we be certain of? Read on for our potted guide.

How much has the planet warmed already?

As part of the Paris climate accord of December 2015, nearly every country in the world agreed to try to limit the increase in global average temperature to 1.5°C above pre-industrial levels.

To work out what that means, we must first know where we are …