My cousin Renate, her husband Bill and I stood far above Grinnell Lake at Glacier National Park and looked down: Its water was a milky blue where the waterfall from the melting Grinnell Glacier above flows into it. Grinnell Glacier is fast disappearing. We already had read that the 150 glaciers that once existed in this park have been reduced to 25, and if temperatures continue to rise at the present rate, they are expected to be gone in 20 years. Some climate scientists predict they'll be gone in 10.
That prediction seems entirely reasonable when we walk down the hallway of the Many Glacier Hotel where photographs taken from the early 1900s to the present are a record of the glaciers' progressive demise.
The Earth still has an impressive number of glaciers (160,000), but nearly every major glacier in the world is shrinking. Glaciers, like ice sheets and sea ice, are affected by warming temperatures. Melting seems to be occurring worldwide - though at different rates.
We have evidence of other changes occurring as a result of these warming temperatures. Oceans are not only warmer, but more acidic; the difference between daytime and nighttime temperatures is decreasing; plants are blooming earlier (some by days, some by weeks) than they used to; animals are moving farther and farther toward the North and South poles. These are all warning signs the Ad Hoc Study Group on Carbon Dioxide and Climate (impaneled by President Jimmy Carter and headed by the meteorologist Jule Charney of MIT) cautioned us against waiting for after the National Academy of Sciences undertook in its first major study of global warming back in 1979.
Because the climate system has a built-in time delay, it's difficult to predict how long it can take for changes that are already set in motion to become evident. Increasing carbon dioxide levels to the atmosphere puts the earth out of "energy balance," so to speak. For balance to be restored, as laws of physics dictate, the entire planet has to heat up, including the oceans, and that process, the Charney panel pointed out, could take "several decades."
The Charney panel concluded with the following paradoxical observation: "We may not be given a warning until the carbon dioxide loading is such that an appreciable climate change is inevitable."
In other words, as I understand it, by the time global warming is so obvious as to be potentially or probably catastrophic, climate change may be so much underway that there is little that can be done to mitigate it, much less reverse it.
• Ursula Carlson, Ph.D., teaches writing and literature at Western Nevada College and for this column referred to Elizabeth Kolbert's "Field Notes from a Catastrophe" published in 2006.