Table 1. Summary of selected extreme event responses
Response by region Late 20th century trend? (ref.) Primary mechanism(s) Secondary mechanism(s)
Northwest
   Increased frequency of extreme hot events Yes (16) Radiative forcing Snow albedo feedbacks
   Decreased frequency of extreme cold events; less severe cold events Equivocal (16) Radiative forcing Snow albedo feedbacks
   Increased frequency and contribution of extreme precipitation events; weaker rain shadows Yes (17, 18, 37) Enhanced cyclonic flow aloft Enhanced atmospheric moisture content
Northeast
   Increased frequency of extreme hot events Yes (16) Radiative forcing
   Decreased frequency of extreme cold events; less severe cold events Yes (16) Radiative forcing
Southwest
   Increased frequency of extreme hot events; longer heat-waves Yes (16) Radiative forcing Surface moisture feedbacks; enhanced anticyclonic flow aloft
   Increased contribution of extreme precipitation events Yes (37) Enhanced low- and upper-level cyclonic flow Enhanced atmospheric moisture content
Southeast
   Increased frequency of extreme hot events Yes (16) Radiative forcing
   Decreased frequency of extreme cold events; less severe cold events Yes (16) Radiative forcing
   Increased frequency and contribution of extreme precipitation events Yes (17, 37) Enhanced convective available potential energy Enhanced coastal moisture convergence