Fresh climate change evidence reinforces concern among scientists, environmentalists and some government officials. World temperatures hit a record high for the third straight year in 2016, U.S. agencies said last week. Last year was the hottest year on record since scientists began tracking Earth's temperature in the 1880s, according to NASA and the National Oceanic and Atmospheric Administration. Average surface temperatures were slightly higher over land and the oceans.

The impact includes rising levels of heat-trapping carbon dioxide and methane gas in the atmosphere, severe coral damage at the Great Barrier Reef off Australia, unprecedented heat in India (123.8° Fahrenheit in May) and expanded glacial melting. Sea ice in the Arctic Ocean and around Antarctica is at record lows for mid-January. "The likelihood of this having happened in the absence of human-caused global warming is minimal," says Michael Mann, a climate scientist at Pennsylvania State University.

Actions are being taken. At a Paris conference in late 2015, governments agreed to phase out fossil fuels this century and shift to renewable energies such as wind and solar power. Still, some specialists fret about irreversible changes. "There are points of no return where, for example, a certain amount of warming triggers unstoppable collapse of glaciers off of Antarctica, even if the planet cools again," says Ben Strauss, vice president of a research group in Princeton, N.J., called Climate Central.

UN official says: "Long-term indicators of human-caused climate change reached new heights in 2016." -- Petteri Taalaas, head of the World Meteorological Organization

Incoming U.S. official says: "The ability to measure with precision the extent of [human] impact and what to do about it are subject to continued debate and dialogue." -- Scott Pruitt, presidential nominee to head the Environmental Protection Agency

Climate expert says: "I expect the [average temperature] record to be broken again within a few years." -- Piers Forster, University of Leeds in England