Complex sentence: A shutdown or slowdown of the thermohaline circulation is an effect of global warming on a major ocean circulation, while a shutdown has not occurred in recorded history, a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) has been observed in recent decades.
Split into simpler sentences: A shutdown or slowdown of the thermohaline circulation is an effect of global warming on a major ocean circulation. While a shutdown has not occurred in recorded history, a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) has been observed in recent decades.