Graphs at the National Climatic Data Center's website (www.ncdc.noaa.gov/indicators) vividly display trends from the late 1800s to the present in atmospheric, surface and ocean temperatures, as well as changes in sea level, snow cover and glacier volume. All point to a warming climate, something many former skeptics now accept as fact.
But is the warming human-caused? The complex interactions of air, sea, ice cover, vegetation and astronomical cycles make projections difficult. Earth's climate has undergone many natural changes in its long history, but no known natural cause explains the current warming trend.
Human causes can. Noncontroversial facts point to human causation:
1. CO2 and other greenhouse gasses in the atmosphere absorb heat.
2. Atmospheric CO2 is now one-third greater than at any time in the past 800,000 years, and it's rising.
3. This spike began around 1800, from fossil fuel use and deforestation.
This century-plus, human-caused spike in heat-trapping atmospheric CO2 corresponds with the 100-plus year uptrend in average temperatures (air, sea and land).
However, I suspect that rather than a suspicion of the science, skepticism toward human causation (and, earlier, for global warming itself) comes more from a perceived threat to ideology and an aversion to taking responsibility.
Salt Lake City