CLIMATE - New Study Shows Independent Evidence Of Global Warming

One of the biggest challenges of climate science seems like it should be one of the easiest; measuring temperatures. The fact is, regular measurements of temperature around the globe didn't being in real earnest until the late 19th century. So when scientists want to understand what temperatures were like prior to that era, they have to use proxies. For example, scientists can tell by the way ice crystallizes what the weather and temperature was like thousands of years ago in ice core samples from polar regions. In the modern era, although there have been steady measurements, they've taken place at different sites at different times with different technologies, which means some heavy math can come into play to normalize that data well enough to see clear trends.

http://www.forbes.com/sites/alexknapp/2013/02/21/new-study-shows-indep