New Paper on Climate Change, Published This Month in “Nature”

A friend sent me this piece on a paper published in Nature suggesting that the effects of climate change could be far worse than most scientists predict.

I respond:

Yes. I’ve seen this. FWIW, I’ve always been suspicious that our current models:

a) use conservative assumptions, and

b) might be missing important feedback loops that are still unknown or poorly understood.

I’m confident that a) is correct because I’ve been told that in face-to-face meetings with climate scientists.

However, these same scientists deny that b) is true, which astounds me.  How do we know what we don’t know?