1. Climate is a long-term average. Long-time averages are much simpler to predict than individual outcomes. You cannot predict the result of a coin toss, but you can be reasonably confident that among 1000 tosses there will be between 400 and 600 occurrences of heads.

2. Scientists, especially young ones, have an incentive to challenge dominating scientific views because that is how you make yourself known in the scientific community. Being known can be transformed to getting the next academic position.