The U.S. had its fourth warmest winter on record. NOAA's Deke Arndt recaps the 2011-2012 winter.

James Roger Fleming presents a historical perspective on how our understanding of Earth's climate system developed through innovations and discoveries by pioneering scientists in the 1800s and 1900s who asked and answered fundamental questions about the causes and effects of global climate change.


Although they are related, meteorology and climatology have important differences, particularly in how scientists develop and use weather and climate models. What makes climatologists think they can project climate scenarios decades into the future when meteorologists cannot accurately predict weather more than two weeks in advance? This presentation by Wayne Higgins of NOAA's Climate Prediction Center clarifies the relationships and differences between weather and climate, as well as the differences between natural climate variability and human-induced climate change.

Climate scientist Michael MacCracken explores some of the scientific, legal, and ethical implications of "geo-engineering" options that have been proposed by some people to address global climate change.

Jackie Richter-Menge describes the "Arctic amplification" phenomenon: how the loss of Arctic sea ice leads to further warming.

In the mid-1980s, the winter sea ice pack in the Arctic was dominated by multi-year ice—ice that had survived at least one summer melt. Today, less than half of the sea ice at winter maximum has survived at least one summer.

The low ice extent recorded this September continued the downward trend seen over the last 30 years. Meanwhile, scientists are finding that the ice cover has grown thinner, making it more vulnerable to melting during the summer.