With some folks wondering why Chicago is experiencing its warmest winter in decades, David Bush, a University of West Georgia geologist, likes to remind people "not to confuse weather with climate."
He acknowledged that wild swings in weather over the years, especially an icy, chilly winter in the Southeast a couple of years ago, can cause people to ask how global warming can be occurring.
But Bush says understanding the difference between weather and climate is key.
Weather is short-term, day-to-day occurrences, such as major air masses from the North that bring arctic air to the normally more temperate South, or warm Southern air making its way North and causing unseasonably warm temperatures.
Climate, instead, is a longer-term, bigger-picture setting.
Bush also talked about how some commentators sow confusion and doubt among the public about the scientific discussion of global change. He cited polls that showed rising skepticism among Americans about climate change, and the stolen email scandal that revealed embarrassing and inappropriate comments from the Climate Studies Unit at East Anglia University a few years ago.
Doubt about whether the planet is warming is also fed by the use of Earth surface temperature data as a direct measure of global warming, Bush said.
He said that it would be difficult to measure temperature trends over the last few years or decades on Earth.
"Where do you stick the thermometer? What matters most? Daytime highs? Nighttime lows? Summer temperatures? Winter temperatures?" Bush said.
Trying to gauge whether the planet is warming (or cooling) in this fashion seems fraught with peril, he said.
But Bush cited conclusive evidence that the planet is warming. "The Earth does the averaging for us. There are many physical and biological characteristics of our planet that clearly indicate the Earth is warming, and has been for decades," he said.
Scientists overwhelmingly agree that the planet is warming.
He cited studies from both hemispheres indicating that 95 percent of the world’s alpine glaciers are retreating. Glacier National Park in Montana has merely 26 named glaciers, compared with 150 in 1850.
If this trend continues, the park could be ice-free by 2030. Other studies show that glaciers in the Himalayas are shrinking so rapidly that the summer flow of the major rivers (Indus, Ganges, Mekong, Yellow, Yangtze) they feed may eventually be seriously affected.
Permafrost regions are thawing in high northern latitudes, causing buildings to sink, roads to crumble, and a variety of other troubles for human infrastructure. The great ice sheets are retreating. The Greenland ice sheet melting began to accelerate in the 1990s. Now the margin of the entire ice mass is melting even in its northernmost reaches. The West Antarctic ice sheet has begun extensive melting, mostly since 2000, and the rate of melting has increased since then.
Sea level is rising, and the rate of rise has accelerated over the last century. A tide gauge on a concrete, open-ocean pier in Duck, N.C., indicates the sea level is now rising at a 1 1/2-foot-per-century rate. In the Pacific, atoll nations such as Tuvalu already are being abandoned because of the rising sea. Soon the Maldives must follow.
The summer sea-ice cover of the Arctic Ocean is shrinking and thinning, and may disappear altogether.
Bush pointed to all of that evidence in saying that it's clear - the planet is warming.
"We should be reading the planet, not thermometers. The Earth is clearly warming and sea level is clearly rising," he said.
The scientific and political debate now centers on what is causing this global warming - natural circumstances (tectonic and astronomical forcing) or human behavior.
Bush argues that both are factors. As a result, he says, it is important to plan for the impact of future warming.
This can be seen clearly on Georgia's coast, where cities such as Savannah and all the communities along Georgia’s barrier islands must begin planning for the inevitability of rising sea level.
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