Forget the melting glaciers. Global warming is revealing itself in subtler ways. Think methane. Swedish bogs are releasing more methane as climate warms and permafrost melts. Methane is a potent greenhouse gas with 25 times the heat-trapping power of carbon dioxide (CO2). With more methane in the air, climate warming could accelerate.
Meanwhile, just as global warming theory predicts, the atmosphere's highest layers are getting colder and thinner. Contrary to expectations, high atmospheric cooling is the way greenhouse gases, such as CO2 and methane, interact with infrared (heat) radiation. At low altitudes, they absorb heat coming up from below and radiate some back downward.
But where astronauts live, these gases release most of their heat out into space, which cools the higher altitudes. The outer atmosphere contracts as it cools, thinning out its density.
Satellites orbiting a few hundred miles out would feel less drag as the air through which they travel becomes thinner.
That's how John Emmert and colleagues with the Naval Research Laboratory in Washington found evidence that this long-expected global warming effect is under way.
They report in the Journal of Geophysical Research that 30 years of tracking data for 27 satellites and space junk show a steady decline in outer atmospheric density.
That's good news for satellite owners who can use less rocket fuel to keep their birds aloft. The news from Sweden is more troubling.
Bacteria in wetlands release methane as they break down organic matter. It's the marsh gas that sometimes ignites to make spooky lights in the night. This activity slows down when bogs freeze.
Northern peat bogs - especially in subarctic Eurasia - are major sources of methane, which spreads throughout the world. Scientists have wondered what will happen as permafrost continues to melt and bogs become even more biologically active.
An international research team recently provided a window into that future. The group, led by Torben Christensen and colleagues at Lund University's GeoBiosphere Science Center in Sweden, studied 30 years of changes in Sweden's Abisko region. Their results, published in Geophysical Research Letters, show Sweden's sub-arctic bogs are losing permafrost rapidly. It's completely gone in some areas. And Dr. Christensen says that, at the Stordalen site, methane emission is up "at least 20 percent, but maybe as much as 60 percent, from 1970 to 2000."
His team report warns that if its findings are typical of the northern subarctic, global warming could accelerate as bogs thaw.
Laurence Smith at the University of California at Los Angeles and colleagues with a joint Russian-American research team expressed a similar concern last January in Nature.
Their studies of vast peat lands in Siberia show the bogs currently absorb a lot of CO2 from the atmosphere while releasing methane. But this could change. If global warming continues, the researchers warn that chemical and biological activity in the bogs could break down organic matter that now stores CO2, releasing a major new source of the gas back into the atmosphere.
The bottom line is that we have to pay attention to subtle effects. We're not going to be drowned by melting glaciers, but we might be bitten by what's sneaking up on us.