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Preventing an extra single degree of heat could make a life-or-death difference in the next few decades for multitudes of people and ecosystems on this fast-warming planet, an international panel of scientists reported Sunday. But they provide little hope the world will rise to the challenge. The Nobel Prize-winning Intergovernmental Panel on Climate Change issued its gloomy report at a meeting in Incheon, South Korea. (Borenstein, 10/8)

The report, issued on Monday by the Intergovernmental Panel on Climate Change, a group of scientists convened by the United Nations to guide world leaders, describes a world of worsening food shortages and wildfires, and a mass die-off of coral reefs as soon as 2040 — a period well within the lifetime of much of the global population. The report “is quite a shock, and quite concerning,” said Bill Hare, an author of previous I.P.C.C. reports and a physicist with Climate Analytics, a nonprofit organization. “We were not aware of this just a few years ago.” The report was the first to be commissioned by world leaders under the Paris agreement, the 2015 pact by nations to fight global warming. (Davenport, 10/7)

At the same time, however, the report is being received with hope in some quarters because it affirms that 1.5 degrees Celsius is still possible — if emissions stopped today, for instance, the planet would not reach that temperature. It is also likely to galvanize even stronger climate action by focusing on 1.5 degrees Celsius, rather than 2 degrees, as a target that the world cannot afford to miss. “Frankly, we’ve delivered a message to the governments,” said Jim Skea, a co-chair of the IPCC panel and professor at Imperial College London, at a press event following the document’s release. “It’s now their responsibility … to decide whether they can act on it.” He added, “What we’ve done is said what the world needs to do.” (Mooney and Dennis, 10/7)

Half a degree may not sound like much. But as the report details, even that much warming could expose tens of millions more people worldwide to life-threatening heat waves, water shortages and coastal flooding. Half a degree may mean the difference between a world with coral reefs and Arctic summer sea ice and a world without them. (Plumer and Popovich, 10/7)