text: Global warming and cooling have closely followed the phases of the PDO. The most significant pattern of PDO behavior is a shift between warm and cool phases that last 20 to 30 years. In 1905, the PDO shifted to its warm phase. In 1946, the PDO changed to its cool phase. In 1977, the PDO returned to its warm phase and produced the current warming. In 2007-8, the PDO turned cold again, so we can expect several decades of naturally-caused global cooling.