Yes. It is unethical to give someone a disease so you can study it. Best we have are case studies of people who got the disease and are being treated for it.
In climate studies, it is not practical to increase temperature or humidity by x% and see the effects. Again, you have case studies - either from the past or from parts of the world that are warming much faster than the rest. Or you can do mesocosm experiments where you warm, say, a square metre of grassland, and see the effects. But then there is a lot of uncertainity in scaling up the findings of such small-scale studies.