The report—authored by hundreds of researchers from 67 countries, who reviewed more than 34,000 scientific references—finds that if the world reaches 2 degrees Celsius of warming above pre-industrial temperatures, extinction will very likely threaten up to 18 percent of species in terrestrial ecosystems. And it notes that mortality is already rising among some species, like corals killed by bleaching , trees damaged by drought , and the mass die-off among kelp forests . People are no exception to the health risks of a warmer world: The report calls out the increased risk of illness from food or water-borne pathogens like freshwater cyanobacteria, as well as cardiovascular and respiratory problems caused by wildfire smoke and atmospheric dust .Rapid warming is also compromising the planet’s capacity to sequester excess carbon from the atmosphere, an ability which has so far helped save humanity from itself. “Some places,” Parmesan continued, “even in areas that are undisturbed, such as intact, old-growth Amazon rainforest and parts of the permafrost in undisturbed areas in North America and northern Siberia, are starting to turn from being overall net sinks of carbon—so sucking up more carbon than they put out—to turning into overall net sources of carbon.”The report also spills significant ink about the fates of cities, both in terms of their vulnerabilities and their power to fight climate change. “I think one of the things that comes out of the report is that cities in and of themselves provide that classic example of a challenge as well as opportunity,” said coauthor William Solecki, of the City University of New York’s Hunter College, at the press conference. “We recognize the world is very rapidly urbanizing—up to 70 percent of the world's population by 2050 will live in cities.”“We're concentrating lots of lots and lots of people in these very small places that are bull's-eyes for any kind of natural disaster, let alone a human-compounded natural disaster from climate change,” adds Jonathan Foley, executive director of Project Drawdown, which advocates for climate action but wasn't involved in the report. “That's actually increasing the risk for really bad things to happen to lots of people all at once. But the good news is that cities could be designed so much better than they are now."