Yes, the global mean temperature is on the rise. The National Climatic Data Center estimates an increase of 0.74 degrees Celsius (1.3 degrees Fahrenheit) in the global mean temperature since the 1800s. The question, of course, is what has caused the warming? There remains a debate between scientists over whether humans contribute to global warming and climate change in a significant way. Some scientists say that mankind has made an impact on global warming by increasing, via industrial and automotive emissions the concentration of greenhouse gases in the lower atmosphere. (Cars release carbon into the atmosphere, creating smog. The smog blankets the area, traps heat and raises the temperature. Industrial output has a similar result.) Others feel the jury is still out and that the science is far from settled. In fact, according to a peer-reviewed study released in the summer of 2011, recent NASA satellite data from 2000 to 2011 shows the Earth is releasing far more heat into space than some scientists have contended, and it predicts far less global warming in the future [source: Forbes].
Regardless of who is right on that score, one thing's for sure: we're lucky we're not stuck in an ice age. "Warming" hasn't always been the watchword. If you widen the time-dilation lens a bit, Earth and its rabble of creatures have experienced in the last 1 million years periods of glaciation that caused enormous change (not to mention ice and cold) to the planet. Just 650,000 years ago ("just" because it's such a speck of geologic time!) the ice buildup was so great that ice pushed deep into the U.S. midwest from Canada and modern-day Germany was hit with ice from Scandinavian climes. Sea levels dropped by about 400 feet (122 meters) and the worldwide temperature overall dropped by 9 degrees F (5 degrees C). Imagine that kind of temperature swing today, with sheets of ice covering vast swaths of the planet. And it wasn't as though that glaciation period hung around for a few decades: It stayed that way for some 50,000 years [source: University of California San Diego]. At least, for all of it's trouble and suffering, the Earth got some gorgeous valleys, enormous lakes and fjords.
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