Centaurs as a hazard to civilization
B. Napier, D. Asher, M. Bailey and D. Steel
Astron. Geophys., 56 (6), 24-30 (2015)

Abstract:
Assessments of the risk posed by near-Earth objects ignore the possibility of a giant comet entering the inner solar system. Bill Napier, David Asher, Mark Bailey and Duncan Steel examine the likelihood and potential consequences of the appearance of such a centaur.

Full published paper at Oxford Journals