For the past 150 years, humans have been burning more and more fuels taken from the ground, combining them with oxygen from the air, and turning them into carbon dioxide that we put back into the atmosphere. This has put more insulation into the atmosphere and has caused an average global warming of about 1.5 degrees Fahrenheit. One-and-a-half degrees does not seem like much, but we must remember that this is an average of temperatures across the globe. Warmer (equitorial) parts of the world have not experienced as much regional warming as the colder (polar) parts of the world. This is because, even though the equatorial region receives more heat from the sun, the warmer air rises more quickly and, through the air and ocean currents, is taken up to the polar regions, which receive less direct heat from the sun. Simply put, more hot air created by climate change at the equator means more hot air sent to the north and south poles, thus causing a more significant warming effect in these areas.
The warmer air and water in the polar regions is what is causing the icecaps in these areas to melt at a faster rate than that at which the ice can re-form through snowfall. This is why the polar icecaps are melting instead of growing. The ice at the poles also reflects ninety percent of the sunlight, where as open ocean absorbs ninety percent of the sunlight. So, with less ice, particularly at the North Pole where there is nothing but ocean underneath, the sun and its heat is absorbed more readily by the ocean, thus causing it to heat up more quickly. The two effects in combination are causing rapid warming and melt-off in the polar regions.
Melting ice is one significant source of increased water volume in the oceans, which in turn causes a general rise in sea level. However, even if there were no melting ice, sea levels would still rise. Why? Because warmer water takes up more space than colder water. These two effects in combination -- increased water volume and warmer water temperatures -- are causing sea levels to rise and are posing significant risks to the over one billion people living on or near coastlines.
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