July 8, 2009

Early seasons due to greenhouse gas effect

Due to increase in atmospheric greenhouse gas concentrations Spring now arrives sooner than it did 50 years ago, say scientists.

Greenhouse gases are chemical compounds that contribute to the greenhouse effect. When in the atmosphere a greenhouse gas allow sunlight (solar radiation) to enter the atmosphere where it warms the Earth’s surface and is re- radiated back into the atmosphere as longer-wave energy (heat). Greenhouse gases absorb this heat and ‘trap’ it in the lower atmosphere.

The rapid increase in atmospheric concentrations of the three main human-made greenhouse gases – carbon dioxide, methane, and nitrous oxide – is clear from the data sets for these gases over the last 420,000 years.

Fossil fuel-burning is the primary anthropogenic source of carbon dioxide, with cement and lime production also being important. Ruminant livestock and rice cultivation are the leading human activities contributing to methane emissions, while agriculture is the primary source of human-made nitrous oxide emissions.

using updated records from the Climate Research Unit at the University of East Anglia, UK it is seen that the onsets of all four seasons have shifted forward by an average of about 1.7 days between 1954 and 2007. During this period, the temperature difference between summer and winter narrowed by about six per cent over land because of warming winters. Both these changes are significantly larger than those observed in the first half of this century from 1900–1953, leading the researchers to infer that human influence, and not natural variability alone, caused the changes.

Warmer winters combined with a premature turn towards spring may be causing earlier spring blooms and bird migrations, effects long reported by biologists. The group's results suggest that these plants and animals are indeed directly responding to a changing climate.

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