5 things to know about the new U.N. report on climate change

Floating dock atop dried-up lakebed in Colombia
A floating dock sits on the parched lakebed of the Suesca lagoon in Colombia.
(Fernando Vergara / Associated Press)

The United Nations’ Intergovernmental Panel on Climate Change published a new report Monday summarizing the latest authoritative scientific information about global warming. Here are five important takeaways.

Blaming humans

The report says almost all of the warming that has 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.

Scientists say that only a fraction of the temperature rise recorded since the 19th century can have come from natural forces.


Paris goals

Almost all countries have signed up to the 2015 Paris climate accord that aims to limit global warming to 3.6 degrees Fahrenheit (2 degrees Celsius) — and ideally no more than 2.7 degrees Fahrenheit (1.5 degrees Celsius) — by the year 2100, compared with the late 19th century.

The report’s 200-plus authors looked at five scenarios, all of which will see the world cross the 2.7-degree threshold in the 2030s — sooner than in previous predictions. Three of those scenarios will also see temperatures rise 3.6 degrees above the pre-industrial average.

Dire consequences

The 3,000-plus-page report concludes that ice melt and sea-level rise are already accelerating. Wild weather events — from storms to heat waves — are also expected to worsen and become more frequent.

Because further warming is “locked in” from the greenhouse gases humans have already released into the atmosphere, some changes will be “irreversible” for centuries even if emissions are drastically cut, the report said.

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Some hope

While many of the report’s predictions paint a grim picture of humans’ impact on the planet and its looming consequences, the IPCC also found that so-called tipping points, such as catastrophic ice-sheet collapses and the abrupt slowdown of ocean currents, are “low likelihood,” though they cannot be ruled out.

Big catch

Meeting the most ambitious goal of the Paris accord — keeping temperature increases to 2.7 degrees by the end of the century — will only be possible through what are known as “negative emissions.” That means sucking more carbon dioxide out of the atmosphere than is added, something the report suggests could be done after 2050. The panel doesn’t explain how this can be done, though, and many scientists are skeptical that it’s possible.