A new United Nations report warns that the severe impacts of global warming would occur by 2040, or in the lifetime of today’s working-age people. In order to avert that scenario, global warming must be contained at 1.5 degrees Celsius above pre-industrial era levels, the U.N.’s Intergovernmental Panel on Climate Change (IPCC) said. The report has been met with a mixture of hope and despair. Some point to the dramatic changes that would be required to hit that mark – even as the U.S., the world’s second-largest emitter of carbon dioxide, rolls back measures designed to slow climate change — while others say that the report affirms that meeting the target is still possible. The IPCC report said global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45% from 2010 levels by 2030, and reach “net zero” around 2050. Accomplishing that goal would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport and cities,” the report added.…