The United Nations-appointed Intergovernmental Panel on Climate Change’s new report on the latest authoritative scientific information about global warming has drawn a lot of attention. Here are five key takeaways from the report:
Nearly all of the warming that’s occurred since pre-industrial times was caused by the release of heat-trapping gases such as carbon dioxide and methane. Much of that is the result of humans burning fossil fuels — coal, oil, wood and natural gas.
The authors say global temperatures are up by 2 degrees Fahrenheit since the 19th century, reaching their highest in over 100,000 years — and only a fraction of that increase could have come from natural forces.
Almost all countries have signed the 2015 Paris climate accord, which aims to limit global warming to an increase of 3.6 degrees Fahrenheit above the pre-industrial average by the year 2100. The agreements says that ideally the increase would be no more than 2.7 degrees Fahrenheit.
But, having considered five likely scenarios, the report’s 200-plus authors concluded that all see the world crossing the 2.7-degree threshold in the 2030s — sooner than in previous predictions. Three of those scenarios also see temperatures rising 3.6 degrees.
The 3,000-plus-page report concludes that ice melt and sea level rise are accelerating.
Wild weather events — from storms to heat waves — are expected to worsen and become more frequent.
Further warming is “locked in” due to the greenhouse gases that humans already have released into the atmosphere. That means that, even if emissions are drastically cut, some changes will be “irreversible” for centuries.
While many of the report’s predictions paint a grim picture of human impact on the planet and the consequences going forward, the U.N. panel also found that so-called tipping points — like catastrophic ice-sheet collapses and the abrupt slowdown of ocean currents — are “low likelihood,” though they can’t be ruled out.
A BIG CATCH
Tthough temperatures are expected to overshoot the 2.7-degree target in the next decade, the report suggests that warming could be brought back down to this level through “negative emissions.”
That means sucking more carbon dioxide out of the atmosphere than is added, effectively cooling the planet again.
The panel says that could be done starting about halfway through this century but doesn’t explain how. Many scientists are skeptical.