Life is very fragile and can only exist under a narrow range of physical conditions. It is in fact purely accidental that Earth can sustain life. Earth is located within the habitable zone of the solar system. It is located just far enough away from the Sun to provide the right surface temperature and gravity conditions to develop an atmosphere with moderate pressure.
The Earth also has the moon's fixed orbit, which eliminates big fluctuations in surface temperature and atmospheric pressure that would result from orbital changes. The ice and moisture that Earth captured from meteors and comets has condensed into oceans and lakes. The atmosphere holds the elements required for life on Earth to form and survive: hydrogen, carbon and oxygen.
There are three vital components to life: water, air and sunlight. Water and air sustain life and sunlight provides energy for organisms to grow. Beyond these three components, the surface magnetic field serves as a trap for electrically charged particles from cosmic rays and thus protects life on the planet from being constantly bombarded by high-energy particles from outer space. Condensation and convection creates the rain that moistens the earth, and clouds absorb and reflect solar radiation.
Although the thickness of the atmosphere is only 0.2 percent of the planet's radius, natural greenhouse gasses finely adjust the surface temperature. Were it not for these gasses partially trapping the solar radiation reflected by the earth's surface, the average surface temperature would be minus 16oC rather than 14oC, which would cover the entire globe with ice and snow and make it unfit for life.
With the advent of the Industrial Revolution, we started using carbon fuels emitting massive amounts of carbon dioxide and other greenhouse gasses into the atmosphere, which has increased the energy that is trapped on the planet. Many climatologists believe this to be the main cause for the average global temperature increase of 0.85oC over the past century.
Computer simulations based on estimates of the expected total amount of greenhouse gas emissions, scientists predicted that the average surface temperature will rise between 2oC and 4oC by the end of the 21st century. Rising temperatures and accelerated water evaporation has led to more frequent and stronger storms, typhoons and hurricanes, while many places such as Africa suffer from severe droughts. A great deal of media coverage has been dedicated to global warming and Al Gore's film An Inconvenient Truth also provides a detailed description.
Global warming can be most easily seen in melting ice sheets in the polar regions. It is frightening to see the speed with which the ice caps in the Arctic and Antarctic have been breaking off. They have been melting for several years. The surface area of the glaciers and ice caps in these areas is shrinking rapidly and this has caused a 0.3m rise in sea levels in the course of a few decades, submerging several low islands. If the ice caps on Greenland and the Antarctic completely melt away within 50 years as predicted, sea levels will rise by more than 10m. By then the world's harbor cities will all become new versions of Venice, while the Netherlands and Bangladesh will lose most of their land.
Earth is the only place in the universe known to harbor life. It is our precious and only home. It not only sustains life but is alive itself. Only if Earth is healthy will all living creatures thrive. To sustain life -- be it human, animal or plant -- we must value this precious blessing, respect and care for each other, and live in peace.
Tsong Tien-tzou is a research fellow at Academia Sinica's Institute of Physics.
Translated by Ted Yang
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