[hosepipe]

1) 50 years,
2) 1000 years,
3) sometime in the future...
4) or not at all...

Duuuhh..
"scientists"... (Eddie Murphy laugh)...

[AntiGuv]

#4 is not an option. There is no doubt that a supervolcano will erupt again at some time in the future.

[DJtex]

One of these super-volcanos erupts on average every 50,000 years or so. Any of them will end civilization, either Toba, or Yellowstone, or Mammoth Mountain in California, or dozens of others.

At 50k years vs. 20 million for an asteriod to hit, this threat is 400 times as likely to end the good times. Also, of course, we're in one of the brief inter-glaciation stages in the Ice Ages that have dominated the earth for 1 to 3 million years. (Eight in the last 750k years). We just don't know how lucky we've been or how tenuous civilization is.