President Obama waves from the doorway of Air Force One on Monday as he prepares to fly to New York for the U.N. General Assembly. Hans Pennink/AP hide caption

itoggle caption Hans Pennink/AP

A glacier in Patagonia, Argentina, calves, with a sudden collapse of ice. Researchers say that the activity that precedes these types of tipping points and the triggers that cause them may follow predictable patterns. Philip Stanley Dickson/iStockphoto.com hide caption

itoggle caption Philip Stanley Dickson/iStockphoto.com

A more than 30,000-year-old dyed flax fiber found in Georgia. It's likely that early humans used plants in the area to color the fibers. Eliso Kvavadze hide caption

itoggle caption Eliso Kvavadze

In the study, cotton-top tamarins grew calmer after they heard music compositions based on their own calm, friendly calls, and became more agitated when exposed to music that contained elements of their own threatening or fearful calls. Bryce Richter/University of Wisconsin-Madison hide caption

itoggle caption Bryce Richter/University of Wisconsin-Madison

Fertilizer is crucial to agricultural production, but its increasing use is leaking nitrous oxide, an ozone-deteriorating gas, into the atmosphere. iStockphoto.com hide caption

itoggle caption iStockphoto.com

These healthy newborn monkeys, Mito and Tracker, developed from embryos containing transplanted DNA. They are named after the dye "mitotracker" used for imaging mitochondria in cells. Oregon National Primate Research Center at OHSU hide caption

itoggle caption Oregon National Primate Research Center at OHSU

The Monterey Bay coastline, Northern California. In a large underwater canyon just offshore, researchers are studying the effects of increasing acidity on marine life. iStockphoto hide caption

itoggle caption iStockphoto

A coral reef near the Caribbean island of Bonaire teems with plant and animal life. Rising water temperatures and increasing ocean acidity pose enormous threats to this wondrous but vulnerable ecosystem. Mark Vermeij hide caption

itoggle caption Mark Vermeij

A longfin damselfish patrols its algae garden off the coast of Bonaire. Damselfish kill a section of the coral, and then wait for algae to grow in the dead spot. On this coral, only a few live sections remain. Henry DeBey hide caption

itoggle caption Henry DeBey

Passengers on a whale-watching ship in Massachusetts Bay. Whale watching is one of many recreational activities that draw people to the waters off the coast of Massachusetts. Kerry Crisley/The Nature Conservancy hide caption

itoggle caption Kerry Crisley/The Nature Conservancy