Plankton collected in the Pacific Ocean with a 0.1mm mesh net. Seen here is a mix of multicellular organisms — small zooplanktonic animals, larvae and single protists (diatoms, dinoflagellates, radiolarians) — the nearly invisible universe at the bottom of the marine food chain. Christian Sardet/CNRS/Tara Expeditions hide caption

itoggle caption Christian Sardet/CNRS/Tara Expeditions

A 2008 view of the leading edge of the Larsen B ice shelf, extending into the northwest part of the Weddell Sea. Huge, floating ice shelves that line the Antarctic coast help hold back sheets of ice that cover land. Mariano Caravaca /Reuters/Landov hide caption

itoggle caption Mariano Caravaca /Reuters/Landov

ADP Co-chairs Daniel Reifsnyder (left) and Ahmed Djoghlaf (center) say their negotiation work is difficult but worth it. "We only have one planet, you know," Reifsnyder says. "We have to protect it." Courtesy of IISD/ENB hide caption

itoggle caption Courtesy of IISD/ENB

Much of the Netherlands is below sea level, including Amsterdam. Urgenda argues that any rise in the sea level could have a huge impact on the country. Ari Shapiro/NPR hide caption

itoggle caption Ari Shapiro/NPR

President Obama, seen here inspecting solar panels on the roof of the Department of Energy, has submitted a U.S. pledge to reduce greenhouse gases. Kevin Lamarque/Reuters/Landov hide caption

itoggle caption Kevin Lamarque/Reuters/Landov

A 2008 view of the leading edge of the Larsen B ice shelf, extending into the northwest part of the Weddell Sea. Huge, floating ice shelves that line the Antarctic coast help hold back sheets of ice that cover land. Mariano Caravaca /Reuters/Landov hide caption

itoggle caption Mariano Caravaca /Reuters/Landov

These beans, grown on test plots at the International Center for Tropical Agriculture in Colombia, can thrive in temperatures that cripple most conventional beans. Courtesy of CIAT/Neil Palmer hide caption

itoggle caption Courtesy of CIAT/Neil Palmer

Staghorn coral planted by scientists in the Florida Keys. Researchers hope to give the same sort of boost to the world's shrinking population of pillar coral, now that they can raise the creatures in a laboratory. Joe Berg/Way Down Video/Mote hide caption

itoggle caption Joe Berg/Way Down Video/Mote

Climate skeptic Willie Soon has argued in the past that too much ice is bad for polar bears. An investigation into Soon's funding found he took money from the fossil fuel industry and did not always disclose that source. iStockphoto hide caption

itoggle caption iStockphoto

A mummy of a Chinchorro child, dating to between 5000 B.C. and 3000 B.C. The Chinchorros were hunter-gatherers who lived in the region between modern-day Peru and Chile. Claudio Santana/AFP/Getty Images hide caption

itoggle caption Claudio Santana/AFP/Getty Images

A lot of the airborne particles in the Earth's atmosphere come from natural sources, such as desert dust (red-orange) and sea salt (blue). But there's also soot from fires (green and yellow) and sulfur emissions (white) from burning fossil fuel. William Putman/ NASA/Goddard hide caption

itoggle caption William Putman/ NASA/Goddard

Smoke rises from chimneys of coal-based power plants in the Sonbhadra District of Uttar Pradesh, India. The Washington Post/Getty Images hide caption

itoggle caption The Washington Post/Getty Images

Rajendra K. Pachauri speaks at the U.N. Climate Change Conference in Lima, Peru, on Dec. 11, 2014. He is stepping down as chairman of the Intergovernmental Panel on Climate Change. Juan Karita/AP hide caption

itoggle caption Juan Karita/AP

Crew members pull an oyster dredge in Tangier Sound of the Chesapeake Bay near Deal Island, Md., in 2013. A study found that the Chesapeake Bay shellfishery is a "hot zone" for ocean acidification. Patrick Semansky/AP hide caption

itoggle caption Patrick Semansky/AP

Robert Davies (standing) and the quartet during a performance of "The Crossroads Project." Musicians include (left to right) Robert Waters, Rebecca McFaul, Anne Francis Bayless and Bradley Ottesen. Andrew McCallister /Courtesy of The Crossroads Project hide caption

itoggle caption Andrew McCallister /Courtesy of The Crossroads Project

To put their probes into the Arctic Ice, researchers hitched a ride on a South Korean icebreaker. Courtesy of Craig M. Lee/University of Washington hide caption

itoggle caption Courtesy of Craig M. Lee/University of Washington

The eruption of Mount Pinatubo in the Philippines in 1991 spewed almost 20 million tons of sulfur dioxide into the atmosphere, causing worldwide temperatures to drop half a degree on average. Arlan Naeg/AFP/Getty Images hide caption

itoggle caption Arlan Naeg/AFP/Getty Images