Top Pro & Con Arguments
Deep ocean currents, not human activity, are a primary driver of natural climate warming and cooling cycles.
Over the 20th century there have been two Arctic warming periods with a cooling period (1940-1970) in between. According to a study in Geophysical Research Letters, natural shifts in the ocean currents are the major cause of these climate changes, not human-generated greenhouse gases.  William Gray, PhD, Emeritus Professor of Atmospheric Science at Colorado State University, said most of the climate changes over the last century are natural and “due to multi-decadal and multi-century changes in deep global ocean currents.” 
Global cooling from 1940 to the 1970s, and warming from the 1970s to 2008, coincided with fluctuations in ocean currents and cloud cover driven by the Pacific Decadal Oscillation (PDO) – a naturally occurring rearrangement in atmospheric and oceanic circulation patterns.  According to Don Easterbrook, PhD, Professor Emeritus of Geology at Western Washington University, the “PDO cool mode has replaced the warm mode in the Pacific Ocean, virtually assuring us of about 30 years of global cooling, perhaps much deeper than the global cooling from about 1945 to 1977.” Read More