Current shifts in abrupt climate change: The stability of the North Atlantic conveyor and its influence on future climate

摘要

When climate shifts abruptly changes occur so rapidly and unexpectedly that human and natural systems have difficulty adapting to, or coping wilt, them. By using palaeoclimatic indicators such as tree and coral growth rings, ice cores and deep sea sediments, climate scientists have uncovered mans' instances of abrupt and relatively short-lived climate changes in the past. These abrupt changes (some taking place within several 50 years) are especially evident over the last 100,000 tears when the planet, under longer-term Mlilankovitch and other forcings, was slipping into and then out of an ice age. Relatively short-term thermohaline (temperature and salt) driven changes ire the vigour and distribution of ocean currents are believed to lie at the heart of the abrupt climate shifts. In particular: thermohaline driven changes between three `modes' of the North Atlantic Conveyor (incorporating the Gulf Stream and North Atlantic Drift) are held to be the key factor explaining abrupt climate shifts over the North Atlantic and adjacent regions. By switching from `on' mode (maximum beat advection) to a `half-on')node (moderate heat advection) to all 'off' mode (little heat advection) and back again, the Northern Conveyor is thought to drive the main pattern in abrupt climate change in the North Atlantic region during the last ice age, This pattern involves multiple sequences of rapid switching from relatively warm periods (interstadials), to cold periods (Dansgaard-Oeschger events) to very cold episodes (Heinrich events) and then back to warm interstadial periods.