The preponderance of evidence is in favor of global warming. But legitimate questions remain about the extent of warming. British modelers foresee an alarming temperature rise of 3.6 to 7.2 degrees Fahrenheit by 2100, dwarfing the single-degree Celsius increase recorded during the past 100 years. Both models reflect a minimum increase in summer temperatures of 1.8 to 3.6 degrees Fahrenheit by the 2030s. With the Great Lakes experiencing their fourth year of water losses, other scientists disagree about how much more data is required to tie the trend to warming worldwide.
Calls vary from two more years to seven years to three decades.
Only from looking at 20 or 30 years of data can we really spot an emerging trend. We don't have that kind of record for global warming yet. Water Sports Affected Measured last month, water levels in Lakes Michigan and Huron are 23 inches below their long-term average. Lake Superior, at the top of the lake system, remains 14 inches below its average level, according to U.S. Army Corps of Engineers records. Held back by sluice gates, Ontario swings less violently because it is mechanically regulated.