Photosynthesis: Physiological and Ecological Considerations

9.5 Photosynthetic Responses to Caron Dioxide 359.5.1 Atmospheric CO 2 concentration keeps risingFIGURE 9.19 Concentration of atmospheric CO 2 from 420,000 years ago to the present.Web Topic 9.5Prehistoric Changes in Atmospheric CO 2The history of atmospheric CO 2on Earth has been one of slow but constant changes,far slower than the rate of today’s atmospheric CO 2changes. The last million year’sworth of history of atmospheric carbon dioxide is trapped in the ice core bubbles.36•These ice core data show thatatmospheric CO 2levels changedbetween 180 ppm (glacial periods)and 280 ppm (interglacial periods)as Earth moved in and out of iceages.•As of January 2007, the CO 2concentration in Earth’s atmospherewas about 0.0383% by volume, or383 ppmv.Web Figure 9.5.A Air bubbles trappedinside frozen ice. Courtesy ofNewScientist.com:http://www.newscientist.com/data/images/ns/cms/dn8369/dn8369-1_500.jpg•ppm, part per million(a) by mass: 1 mg/kg(b) by volume: 1 mL/10 3 L (cm 3 /m 3 )18