Nations have delayed curbing their fossil-fuel emissions for so long that they can no longer stop global warming from intensifying over the next 30 years, though there is still a short window to prevent the most harrowing future, a major new United Nations scientific report has concluded. Humans have already heated the planet by roughly 1.1 degrees Celsius, or 2 degrees Fahrenheit, since the 19th century…but that’s only the beginning. Even if nations started sharply cutting emissions today, total global warming is likely to rise around 1.5 degrees Celsius within the next two decades, a hotter future that is now essentially locked in. …A second report, set to be released in 2022, will detail how climate change might affect aspects of human society, such as coastal cities, farms or health care systems. A third report, also expected next year, will explore more fully strategies to reduce greenhouse gas emissions and halt global warming.