The manufacturer (IPCC) says that based on their best information and models if you do not get your oil changed in your car every 10k miles it will lead to increased engine wear which can lead to other problems. Every reputable mechanic (climate scientists)agrees that 10k is a reasonable estimate and that people who drive over that limit will lead to even worse results on average.
Now lets say you've got a smart uncle Jim. He's a damned good electrician and he's been driving his car over 10k without changing his oil for years and he says his car is still running great. He brings it into the shop and the mechanic says his mileage is down and there's some wear on the engine that they can see. Since your uncle Jim can't see the wear that these mechanics see he accuses them of trying to rip him off and drives the vehicle even farther past the 10k miles just to prove them wrong.
This is the climate change debate in a car analogy. There's tons of variables that can affect how long a car lasts and no good mechanic can tell on what day a car will break, but over a long enough timeline they can say for sure that it will result in degraded performance.