What is causing this heating? Various greenhouse gases such as carbon dioxide, methane and nitrous oxide trap the incoming energy from the Sun. The greenhouse gases let the Sun's energy enter the atmosphere, but stop some of it from leaving. The amount of extra heat trapped in the atmosphere by these greenhouse gases is equal to the energy released by some 400,000 Hiroshima atom bombs each day.
The current carbon dioxide levels are about 40% higher than they were in the 19th century. They are also at their highest levels for the last 800,000 years. Indeed, over the last 800,000 years, carbon dioxide levels stayed within the range of 170 - 280 ppm until the Industrial Revolution.
That makes the sudden recent jump to 400 ppm over the last two centuries really quite astonishing. In fact, in the year 2013, the carbon dioxide levels grew at the fastest rate ever measured since reliable global records began.
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