Warmth in north pushes spring forward.When viewed from space, the northern end of the globe is looking a tad greener these days. Satellite measurements from 1981 to 1991 have revealed a noticeable increase in vegetation and a lengthening of the growing season growing season, period during which plant growth takes place. In temperate climates the growing season is limited by seasonal changes in temperature and is defined as the period between the last killing frost of spring and the first killing frost of autumn, at which , a team of scientists reports. The group attributes the greening to an increase in northern temperatures. Ranga B. Myneni of Boston University Boston University, at Boston, Mass.; coeducational; founded 1839, chartered 1869, first baccalaureate granted 1871. It is composed of 16 schools and colleges. and his colleagues discovered the enhanced plant growth by analyzing data from radiometers flying on weather satellites. The radiometers measure different wavelengths of light reflecting off Earth's surface Noun 1. Earth's surface - the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water" surface . Because plants absorb most of the visible light hitting the ground, regions with vegetation reflect far less light than does exposed soil, snow, or water. Over the 10-year span, areas between 45 [degrees] N and 70 [degrees] N showed a 12 percent increase in spring and summer plant growth. At the same time, the annual growing season extended. By 1991, vegetation was appearing about 8 days earlier and remaining green about 4 days later than it had in 1981, report Myneni and his colleagues in the April 17 Nature. Analysis of more recent data shows that these trends have continued through at least 1994, says Myneni. The new findings confirm a report last year by Charles D. Keeling keeling the marking of ewes by the ram when they are mated by the marking on the ewe of paint or chalk from the sternum of the ram. of the Scripps Institution of Oceanography Scripps Institution of Oceanography: see California, Univ. of. in La Jolla La Jolla (lə hoi`yə), on the Pacific Ocean, S Calif., an uninc. district within the confines of San Diego; founded 1869. The beautiful ocean beaches, in particular La Jolla shores and Black's Beach, and sea-washed caves attract visitors and , Calif., who collaborated with Myneni on the current study. By tracking carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. concentrations in the atmosphere, Keeling and his colleagues had detected signs of enhanced photosynthesis in the north, with springtime growth appearing a week earlier than it had previously (SN: 7/13/96, p. 21). Myneni, Keeling, and their coworkers suggest that warming in the north has triggered the bloom. Large sections of Alaska, northwestern Canada, and northern Europe and Asia have warmed in recent decades, melting snow earlier in the year. The scientists remain unsure why temperatures have climbed. The cause could be a natural change, or it could be greenhouse warming rearing its ugly head, notes Myneni. |
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