Understood, though I didn't have that idea about #2. My impression was that it was a well-known problem (going back to talk radio and Rupert Murdoch properties, and then growing and being more in our face with everything the Internet enabled).
Maybe one of the problems is that, online, a flood of dozens of angry tweets stomping on someone, by (for the sake of argument) a small minority of people who are having a bad day... has the effect that people are routinely (almost systematically) stomped, because there's always some dozens of people having a bad day? And they all sound the same, so maybe it's a rotating vocal minority that looks like a bigger problem than it is?
Regarding death threats...
I think we have different expectations about the possibility of gov't help (I'm still a bit Pollyanna on this). Local police might or might not have the resources to take the report and coordinate with federal resources, but it's likely inter-state, so the victim could go direct to the FBI.
I'm sure I've read news stories of the senders of death threats being tracked down by law enforcement.
And, I suppose the sender just might be linked to a domestic group/network (or foreign agitators) that the FBI is already tracking.
If the researchers are under a university or NGO, are they getting support from their organization, or do they need to confront the org's administration into interfacing better with law enforcement regarding death threats?
(I'm speaking of baseline situation in recent years; I have no idea what the situation at the FBI is this week, given the various gov't disruption going on, and the keyword "climate" being targeted by some. Even if the situation is complicated at the moment, maybe lead the reporting of a crime and request for assistance with the death threat part, and then the details relevant to the investigation/analysis include that the victim is a climate researcher?)
If all else fails, an org's lawyer (and investigator they hire) might also identify doxing and egging activity (especially online) that's traceable to death threats, and be able to do more with law enforcement and/or civil courts.