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EISEROWITZ'S STUDY OF risk perception found that Americans fall into "interpretive communities"—cliques, if you will, sharing similar demographics, risk perceptions, and worldviews.

On one end of this spectrum are the naysayers: those who perceive climate change as a very low or nonexistent danger. Leiserowitz found naysayers to be "predominantly white, male, Republican, politically conservative, holding pro-individualism, pro-hierarchism, and anti-egalitarian worldviews, anti-environmental attitudes, distrustful of most institutions, highly religious, and to rely on radio as their main source of news."

This group presented five rationales for rejecting danger: belief that global warming is natural; belief that it's media/environmentalist hype; distrust of science; flat denial; and conspiracy theories, including the belief that researchers create data to ensure job security

We might wonder how these naysayers, who represent only 7 percent of Americans yet control much of our government, got to be the way they are. A study of urban American adults by Nancy Wells and Kristi Lekies of Cornell University sheds some light on environmental attitudes. Wells and Lekies found that children who play unsupervised in the wild before the age of 11 develop strong environmental ethics. Children exposed only to structured hierarchical play in the wild—through, for example, Boy Scouts and Girl Scouts, or by hunting or fishing alongside supervising adults—do not. To interact humbly with nature we need to be free and undomesticated in it. Otherwise, we succumb to hubris in maturity. The fact that few children enjoy free rein outdoors anymore bodes poorly for our future decision-makers.

THE ALARMISTS AND THE ACROBAT ON THE OTHER END of Leiserowitz's spectrum of perception regarding global warming is an interpretive community he calls the alarmists, generally comprised of individuals holding pro-egalitarian, anti-individualist, and antihierarchical worldviews, who are supportive of government policies to mitigate climate change, even so far as raising taxes. Members of this group are likely to have taken personal action to reduce greenhouse gas emissions.

Collectively, alarmists compose 11 percent of Americans, with the remaining interpretive communities falling considerably closer to the alarmists than the naysayers in the spectrum—suggesting the gap might be cinched by sustained public education on the neighborhood dangers likely to arise in a changed global climate.

Hurricane Katrina provided a wake-up call for how bad it can get in the neighborhood, and may prove a tipping point itself.

Yet long before its rampage, American kids were coloring pictures of the first icon of global environmentalism, the Amazon. Its billion-plus acres of rivers and rainforest—its trees collecting and containing excessive greenhouse gases from the atmosphere—were our primer for the revolutionary notion that the earth's neighborhoods are interdependent. Today Amazonia is the most famous of Schellnhuber's tipping points. For a generation, kids have grown up learning that the Amazon is at risk from massive deforestation. But even if clearcutting were to halt, climate models forecast that a warming globe will convert the wet Amazonia forest into savanna within this century, and the loss of trees will render the region a net CO2 producer, further accelerating global warming.

Hydrofluorocarbons (HFCs) HFCs are man-made chemicals, many of which have been developed as alternatives to ozone-depleting substances (ODS) for industrial, commercial, and consumer products.

The global warming potentials of HFCs range from 140 (HFC-152a) to 11,700 (HFC-23).

The atmospheric lifetime for HFCs varies from just over a year for HFC-152a to 260 years for HFC-23.

Most of the commercially used HFCs have atmospheric lifetimes less than 15 years; e.g., HFC-134a, which i sused in automobile air conditioning and refrigeration, has an atmospheric life of 14 years.

Perfluorocarbons (PFCs) Primary aluminum production and semiconductor manufacture are the largest known man-made sources of two perfluorocarbons – CF4 (tetrafluoromethane) and C2F6 (hexafluoroethane).

The GWP of CF4 and C2F6 emissions is equivalent to approximately 6,500 and 9,200 tonnes, respectively. PFCs are also relatively minor substitutes for ozone-depleting substances (ODSs).

PFCs have extremely stable molecular structures and are largely immune to the chemical processes in the lower atmosphere that break down most atmospheric pollutants. Not until the PFCs reach the mesosphere, about 60 kilometers above Earth, do very high-energy ultraviolet rays from the sun destroy them. This removal mechanism is extremely slow and as a result PFCs accumulate in the atmosphere and remain there for several thousand years.

The estimated atmospheric lifetimes for CF4 and C2F6 are 50,000 and 10,000 years respectively.

Sulfur Hexafluoride (SF6) The global warming potential of SF6 is 23,900, making it the most potent greenhouse gas the IPCC has evaluated.

SF6 is used for insulation and current interruption in electric power transmission and distribution equipment, in the magnesium industry to protext molten magnesium from oxidation and potentially violent burning, in semiconductor manufacturing to create circuitry patterns on silicon wafers, and as a tracer gas for leak detection.

Like the other high GWP gases, there are very few sinks for SF6, so all man-made sources contribute directly to its accumulation in the atmosphere. Measurements of SF6 show that its global average concentration has increased by about 7% per year during the 1980s and 1990s, from less 1 ppt in 1980 to almost 4 ppt in the late 1990’s (IPCC, 2001).

HFC-134a has an atmospheric lifetime of about 14 years and its abundance is expected to continue to rise in line with its increasing use as a refrigerant around the world.

The only significant emissions of HFCs before 1990 were of the chemical HFC-23

Between 1978 and 1995, HFC-23 concentrations have increased from 3 to 10 parts per trillion (ppt), and continue to rise. Since 1990, when it was almost undetectable, global average concentrations of HFC-134a have risen significantly to almost 10 ppt (parts per trillion).