To establish the reality of anthropogenic climate change, one must demonstrate four points. It must be shown that the planet is warming, atmospheric concentration of carbon dioxide (and other green house gases) is increasing, human activity is causing this increase and the overabundance of these gases cause warming.
Let us first examine the claims that warming is occurring at all. In the Intergovernmental Panel on Climate Change's (IPCC) fourth assessment on climate change, released in 2007, the change in average global temperature was reported as 0.74 degrees Celsius, up from the 0.6 degrees reported in their third assessment, issued in 2001. To cite the lower number is to cite out of date research. And just for the record, the usefulness of an average global temperature statistic is not disputed as long as it's calculated correctly (geometrically).
What about the "global cooling" scare of the 1970s? There is a simple explanation: From the early 20th century until the 1950s, certain industrial techniques were quite "dirty," emitting not just carbon compounds but also sulfur compounds and other impurities. These accumulated in the atmosphere and reflected sunlight back out into space. However, these inefficiencies were later addressed and remedied, so as the airborne particles degraded cooling ceased and warming recommenced.
Now, a few questions that are answered quickly and easily. Are atmospheric CO2 levels up? Certainly. At present, the concentration is approximately 375 parts per million (ppm), the highest in 650,000 years, over which time the average was 180-300 ppm. Is human activity responsible for these increases? Absolutely. The burning of fossil fuels is the primary cause.
Does a higher concentration of atmospheric CO2 cause warming? Contrarians like to point out that there is a lag between CO2 concentration increase and temperature increase. That's true; such a lag exists for the same simple reason that there is a lag in the cooling caused by other compounds. The effects, as expected, are not immediate. CO2 will trap radiation over time, but you can't expect the effects to be instantaneous. That's common sense. Many models for climate change show the causal relationship between CO2 and temperature. Are they perfect? Of course not. But they align surprisingly well and are refined to a higher degree of precision each year. It would be regrettable if the transient issue of experimental uncertainty, declining as it is, were to distract from the bigger issue: that of climate change itself.
The answer to the big question of human responsibility is yes, human activity is causing climate change. The IPCC concluded with 90 percent certainty that humans are responsible for the majority of warming. According to the combined output of over a dozen models, human activity can be attributed to virtually all temperature increases of the late 20th century.
There is a near absolute consensus among the scientific community that this is the case. For evidence of such agreement, look no further than a 2004 study that found, of nearly 700 papers in Science that addressed the question of human responsibility, not a single one argued that humans are not the primary cause.
The big picture is, like too many other issues, that climate change has become a partisan matter. To quote Roger Pielke Jr., "Republican political agendas require confronting current scientific consensus." What a shame that there is not enough intellectual honesty among many conservatives to set aside ideology in favor of integrity.
Sources - realclimate.org, IPCC Fourth Assessment Report, Science, Statistical Science, "Proceedings of the National Academy of Sciences of the United States of America"
