berretta as I understand it the concentration of carbon dioxide (CO2) in Earth's atmosphere determines its contribution to the greenhouse effect and the rates of plant and algal photosynthesis. The concentration has increased markedly in the 21st century, at a rate of 2.0 ppm/yr during 2000–2009 and faster since then. It was 280 ppm in pre-industrial times, and has risen to 400 ppm (parts per million) as of May 2013, with the increase largely attributed to anthropogenic sources. About 57% of the CO2 emissions go to increase the atmospheric level, with much of the remainder contributing to ocean acidification. Despite its relatively small overall concentration in the atmosphere, CO2 is an important component of Earth's atmosphere because it absorbs and emits infrared radiation at wavelengths of 4.26 µm (asymmetric stretching vibrational mode) and 14.99 µm (bending vibrational mode), thereby playing a role in the greenhouse effect. The present level appears to be the highest in the past 800,000 years and likely the highest in the past 20 million years, but well below 10% of its 500-million-year peak. The problem I have is that humans have only been on this planet for about 2-3 million years so 500 million years ago is perhaps of little relevance. I have no qualifications in this area so tend to go with the majority of scientists who do.
