Throughout history, the
earth's atmosphere has changed.
There have been seven periods of glacial development and retreat in the last 650,000 years alone, with the sudden end
of the last ice age around 11,700 years ago marking the beginning of the modern climate period and of human civilization.
Much of these climate changes are due to very small differences in the orbit
of the Earth that modify the amount of solar energy obtained by our planet.
The current warming trend is of special significance because much of it is highly likely to be the result of human activity
since the mid-20th century and to continue at a pace that is extraordinary over decades to centuries (more than 95 percent probability).
Satellites orbiting the Earth and other technological advancements have allowed scientists to see the big picture,
gathering on a global scale many different types of knowledge about our world and its environment.
This body of evidence, gathered over several
years, shows the signs of a changing environment.
In the mid-19th century, the heat-trapping nature of carbon dioxide and other gases was demonstrated.
The scientific basis is their ability to influence the transfer of infrared energy through the atmosphere.
Ice cores from Greenland, Antarctica, and tropical mountain glaciers suggest that the atmosphere
of the Planet is reacting to changes in the levels of greenhouse gases.
Tree rings, ocean sediments, coral reefs, and layers of
sedimentary rocks can also be found as ancient evidence.
This ancient data, or paleoclimate, shows that current warming occurs about
ten times faster than the average rate of warming of ice-age recovery.
Human-active carbon dioxide grows more
than 250 times faster than it did from natural resources after the ice age.
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