Two central questions in Climate Science are: is our planet warming, and, if so, are human activities primarily responsible? The 2007 Report from the Intergovernmental Panel on Climate Change (IPCC): The Physical Science Basis, makes it very clear.
This report, free and available online, consisting of 996 pages of text, data and graphs, states on page 252, "Instrumental observations over the past 157 years show that temperatures at the surface have risen globally… " and "An increasing rate of warming has taken place over the past 25 years, … ." Ten indicators of a warming world were discussed in an earlier article here (9/5/10) and can be found in www.ICSUSA.org .
On page 665 this same IPCC report states, "Human-induced warming of the climate system is widespread." Also, "Greenhouse gas forcing has very likely (greater than 90 percent probability) caused most of the global warming over the past 50 years." Physicist John Cook published the following chart based on the many lines of evidence and data in the IPCC report and the NOAA "State of the Climate 2009" report, also available free and online. His chart highlights 10 indicators of the human fingerprint on climate change.
We have room today to discuss just two of these. However, climateprogress.org, Aug. 10, 2010, does provide information and peer reviewed references for all 10.
Let's look at one of the indicators in the chart, "Less oxygen in the air." When we combust carbon, from coal, oil or natural gas in order to extract the energy from it, we use two oxygen atoms to convert each carbon atom to carbon dioxide. This is the basic chemistry of that process. This oxygen has to come from someplace and indeed, it does: it comes from the air around us. Careful measurements of the oxygen content of our atmosphere show the levels to be falling in conjunction with the rising amount of carbon dioxide which is exactly what one would expect.