Fortunately, expertise is not limited to a single concrete topic. There are experts in climate change from a socio-economic perspective, which are able to do science in such complex environments :)
If such experts existed, centrally planned economies would work wonderfully. Unfortunately, they don't. For sufficiently complex problems, the knowledge is diffuse across a wide range of individuals and there is no one expert we can turn to. That's why debate, and tolerating dissent, is important.
Huh? These experts absolutely exist - look e.g. at iSAGE during the pandemic in the UK. They combined epidemiology with sociology to provide a more comprehensive view of the situation. It's just that you ultimately have to listen to people saying "do X, which is expensive". Governments don't on the whole tend to love that.
Dissent is important, within reason. Things like claiming a medication we know is ineffective can cure Covid in the face of 99% of the medical establishment telling you you're a moron is not within reason, for example.