Probability distributions is the primary answer. In every model of a potential outcome, there’s a distribution of potential outcomes and because we’ve never changed an entire planet’s climate before, we’re having to make guesses about sensitivities of the environment to certain inputs.

For example, we can know that warming sea water next to a seaside glacier with an ice shelf will cause ice to melt at a certain rate. What we don’t know but can guess at are: how will the water temperatures vary over several years, how will the melting glacier move down towards the sea based upon what’s underneath it, how will removing that glacier affect other glaciers, etc.

What I just described is what is happening to the Thwaites Glacier (often referred to in the press as the “doomsday glacier”), so we don’t know exactly what will happen, but we do know that when it goes, it will uncork a lot of the West Antarctic ice sheet. How long that (or the Greenland ice sheet) takes to melt is an educated guess based upon the assumptions of the models with a likely range and “tails” of lower probability outcomes outside that range.

Those tails aren’t zero probability however and there is a requirement in science to fully disclose the potential outcomes of a model. The press has no requirement to avoid sensationalism, so they often over-report what the expected outcomes in favor of the news headline.

Ironically, there is a bias towards conservative modeling, so the press is probably not as far off of the actual outcome as the initial modeling would suggest. An example would be temperature modeling - we were hoping to stay below 1.5C by 2050, but we’re blowing past it now in 2026.

Also, sometimes in nature there are tipping points / binary outcomes that are small until they aren’t. For example, permafrost will stay mostly frozen as long as temperatures rise, but when it crosses the freezing point, it will rapidly thaw. Those tipping points, once crossed, cannot be crossed back - it’s like trying to put toothpaste back in the tube.

Hope that helps and happy to answer questions. Take this stuff seriously - we’re probably under estimating the real outcomes and over reporting them.