HISTORIC MT. BAKER GLACIER FLUCTUATIONS—GEOLOGIC EVIDENCE OF THE CAUSE OF GLOBAL WARMING

Advance and retreat of glaciers on Mt. Baker show distinct oscillations with periods of ~30 ± 5 years. From ~1890 until the late 1920s, glaciers on Mt. Baker were well downvalley from their present termini, and then retreated rapidly from the late 1920s to the late 1940s. Glaciers readvanced again from the late 1940s and early 1950s to 1977, then retreated rapidly from ~1977 to the present. These glacial oscillations are mirrored by global temperature curves, North Pacific sea surface temperatures (PDO), North Atlantic sea surface temperatures (NAO), European alpine glaciers, and Greenland ice cores (GISP2). Similar earlier glacial fluctuations are recorded in Little Ice Age moraines that show cooler climates at about 1790, 1850, and 1890. Oxygen isotope ratios in Greenland ice cores show that these cycles have continued over the past millennium.

These late Pleistocene, global, climate changes have implications for understanding present–day global warming. The global climate has been warming (and cooling) not just since modern atmospheric CO2 has risen, but over the past millennium, long before rising atmospheric CO2 from manmade emissions. Although atmospheric CO2 is now at an all time high, 80% of manmade CO2 emissions occurred after 1945. However, more than half of the global warming of the past century occurred before 1945, mostly between 1890 and 1940, when it could not have been caused by increased atmospheric CO2. During the 30 years (1945 to 1977) following the most dramatic rise in CO2 (1945), global climates actually cooled, raising the question, if increasing CO2 is the cause of global warming, why did global climates cool during this dramatic rise in CO2? If rising CO2 causes global warming, temperatures should have increased, rather than decreased, during this 30 year period.

Extrapolation of previous cyclical global climate changes suggests that the present global warming should begin to decline between now and about 2010, remain cool until about 2040, then warm again from about 2040 to about 2070 before entering another cool cycle from 2070 to 2100. The total amount of global warming to 2100 should be about 1° F, rather than 5° F to 11° F predicted by the IPCC.