James Hansen and Michael Mann. Michael Mann in this interview gives a moderately alarmist view of coming climate change. He mentions that James Hansen recently expressed an even more alarmist view about climate change. The thing with Hansen, he makes bold predictions that make the larger climate change community uncomfortable, and he either turns out to have gotten it right, or it turns out even worse than he predicted.
The mainstream climate change community always seems stuck in the mindset of denying how bad and how fast the changes are happening. When they first started thinking about climate change, they thought in terms of thousands of years. When measurements showed it happening right before their eyes (in the 1980s), they started thinking "Maybe it can happen in centuries." By the 90s, they started scrambling to check paleoclimate records to see if climate change could happen even faster. Now they are staring at catastrophe happening in decades, and severe consequences happening right now.