Upper ocean heat content has increased significantly over the past two decades. An estimated 70 percent of the excess heat has accumulated in the top 2,000 feet of the ocean, and the rest has flowed into deeper ocean layers.

In 2012—for the 23rd consecutive year—mountain glaciers worldwide lost more mass through melting than they gained through new snow accumulation. The retreat of the majority of mountain glaciers worldwide is one of the clearest signs that climate is warming over the long term.

In 2013, global average sea level was 1.5 inches above the 1993-2010 average, which is the highest yearly average in the satellite record (1993-present). Overall, sea level continues to rise at a rate of one-eighth of an inch per year.

 Arctic sea ice extent shrunk down to 2.0 million square miles (5.1 million square kilometers) in September 2013—18 percent below the 1981-2010 average, but larger than record low set in 2012.

Climate change is a global phenomenon, affecting weather events around the world.

In October 2003, a little-known think tank in the Department of Defense quietly released a report warning that climate change could happen so suddenly it could pose a major threat to our country's national security. Why was the Pentagon worried about abrupt climate change? Because new evidence from Greenland showed it had happened before. 

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