Spring is now arriving a week earlier in the Northern Hemisphere than it did twenty years ago and rising atmospheric temperatures are the most likely cause, according to researchers at the Scripps Institution of Oceanography. Their findings indicate that climate change is measurably altering earth’s carbon dioxide cycle. Dr. Charles Keeling, an author of the study which was published in Nature in July, 1996, noted that "our measurements of the increase in seasonal changes of carbon dioxide levels conform very well with temperature measurements going back to the late 1950s showing that surface temperatures are getting warmer." In addition, Keeling noted, "Small changes in temperature -- averaging only a fraction of a degree Celsius a year -- are nevertheless causing fairly large changes in plant growth."
Each spring and summer, the level of carbon dioxide in the atmosphere drops as plants absorb the gas, and then rise again as plants die and decay, releasing carbon dioxide during fall and winter. According to the study, the researchers at the Scripps Institution found that seasonal swings in carbon dioxide concentrations have grown 20 percent larger in Hawaii and 40 percent larger in Alaska since the early 1960s.
One result is that the spring decline in carbon dioxide now occurs seven days earlier than it did during the mid-1970s. "The drawdown in carbon dioxide is earlier than it was before and that’s probably the key to the whole picture, because it looks like the growing season has lengthened," Keeling told Science News.
Citation: "Increased activity of northern vegetation inferred from atmospheric CO2 measurements," Nature, Vol. 382, July 11, 1996. See also .