Five Reasons We Need To Act Now on Climate Change: As world leaders in Paris negotiate cuts in greenhouse gases, scientists say we face urgent reasons to take action.

http://news.nationalgeographic.com/2015/12/151204-climate-paris-disease-antarctic-arctic-ice-melt-acidification-fish-co2/

The city of Jiangyin is experiencing large-scale construction of housing developments to keep up with China’s growing population. More people on Earth will mean increased greenhouse gases unless global leaders find ways to curb them.

The West Antarctic Ice Sheet

Since the 1970s warming ocean waters have melted a significant section of ice in the Amundsen Sea in the Southern Ocean – so much that collapse of a far greater mass of ice may be inevitable. Scientists from NASA and elsewhere, based on a half-dozen studies in the past two years, now believe it may be too late to stop  so much Antarctic ice from melting that it would send sea levels rising 16 feet more, inundating regions home to hundreds of millions of people. What may still be
possible, however, is for humans to control just when that might happen.Antarctica's South Dakota-sized Thwaites Glacier has dwindled so substantially in recent decades that it is now held in place by a weak tongue of ice. Thwaites and the melting of another nearby glacier already are causing a modest amount of sea level rise – even as thousands of years of excessive cold to the east means the amount of Antarctic snow and ice overall is still growing. The problem: Once Thwaites goes completely it would likely destabilize other sections of the West Antarctic Ice Sheet, triggering a far more massive melt. No one can say how much we need to thwart rising temperatures to keep this melting to a trickle. But many scientists seem to agree in principle: Curb emissions fast enough, and this expected collapse could stretch out over several thousand years – plenty of time for humans to prepare. But if we don't act with haste, the collapse could be well underway by the end of this century. "What keeps you up at night is that the thresholds are often not well-defined," says Jason Smerdon, with Columbia University's Earth Institute. "At some point, they can cause very rapid changes in the system. But exactly when is hard to pin down."