GLOBAL CHANGING
Earth is currently in a period of warming. Over the last
century, Earth's average temperature rose about 1.1°F (0.6°C). In the last two
decades, the rate of our world's warming accelerated and scientists predict
that the globe will continue to warm over the course of the 21st century. Is
this warming trend a reason for concern? After all, our world has witnessed
extreme warm periods before, such as during the time of the dinosaurs. Earth
has also seen numerous ice ages on roughly 11,000-year cycles for at least the
last million years. So, change is perhaps the only constant in Earth's
4.5-billion-year history.
Scientists note that there are two new and different twists
to today's changing climate: (1) The globe is warming at a faster rate than it
ever has before; and (2) Humans are the main reason Earth is warming. Since the
industrial revolution, which began in the mid-1800s, humans have attained the
magnitude of a geological force in terms of our ability to change Earth's
environment and impact its climate system.
Since 1900, human population doubled and then doubled again.
Today more than 6.5 billion people inhabit our world. By burning increasing
amounts of coal and oil, we drove up carbon dioxide levels in the atmosphere by
30 percent. Carbon dioxide is a "greenhouse gas" that traps warmth
near the surface.
Humans are also affecting Earth's climate system in other
ways. For example, we transformed roughly 40 percent of Earth's habitable land
surface to make way for our crop fields, cities, roads, livestock pastures,
etc. We also released particulate pollution (called "aerosols") into
the atmosphere. Changing the surface and introducing aerosols into the
atmosphere can both increase and reduce cloud cover. Thus, in addition to
driving up average global temperature, humans are also influencing rainfall and
drought patterns around the world. While scientists have solid evidence of such
human influence, more data and research are needed to better understand and
quantify our impact on our world
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