The pseudocategory of “climate scientist” was invented by the UN’s IPCC. So the UN has everything to do with it.
Climate science is distinguished from climatology by practitioners in the field by the fact that climate science relies heavily on numerical models for the study of climate processes, whereas climatologists primarily use statistical methods to study climate. Climate scientists also use statistical methods to study the output of their numerical models and to compare these results with observations. The distinction is in the wide use of numerical models by climate scientists. These numerical models (in contrast to, say, statistical models or conceptual models) are based on the fundamental laws of physics and have essentially the same basic equations as models used by fluid engineers to study fluid motions in combustion chambers, flow around airplane bodies, and flow in pipes and ducts.