"CLIMATE CHANGE"
Climate change is a
significant and lasting change in the statistical distribution of
weather patterns over periods ranging from decades to millions of years.
It may be a change in average weather conditions, or in the distribution of
weather around the average conditions (i.e., more or fewer extreme weather
events). Climate change is caused by factors such as biotic processes,
variations in solar radiation received by Earth, plate
tectonics, and volcanic eruptions. Certain human activities
have also been identified as significant causes of recent climate change, often
referred to as "global warming".
On the broadest scale, the
rate at which energy is received from the sun and the rate at which it is lost
to space determine the equilibrium temperature and climate of Earth. This
energy is distributed around the globe by winds, ocean currents, and other mechanisms
to affect the climates of different regions. Factors that can shape climate are
called climate forcing’s or "forcing
mechanisms". These include processes such as variations in solar
radiation, variations in the Earth's orbit, mountain-building and continental
drift and changes in greenhouse
gas concentrations. There are a variety of climate
change feedbacks that can either amplify or diminish the
initial forcing. Some parts of the climate system, such as the oceans and ice
caps, respond slowly in reaction to climate forcing’s, while others respond
more quickly.
Life affects climate through
its role in the carbon and water cycles and
such mechanisms as albedo, evapotranspiration, cloud formation, and weathering. Examples
of how life may have affected past climate include: glaciation 2.3
billion years ago triggered by the evolution of oxygenic photosynthesis, glaciation
300 million years ago ushered in by long-term burial of resistant
detritus of vascular land plants (forming coal), termination
of the Paleocene-Eocene Thermal Maximum 55
million years ago by flourishing marine phytoplankton,
reversal of global warming 49 million years ago by 800,000 years
of arctic azolla blooms, and global cooling over the past 40 million
years driven by the expansion of grass-grazer ecosystems.
