'Unequivocal' that human influence has warmed the planet, UN climate panel finds

A United Nations climate panel has confirmed -- in its strongest language ever -- that the impacts of human-caused climate change are severe and widespread, and that while there is still a chance to limit that warming, some impacts will continue to be felt for centuries.

"It is unequivocal that human influence has warmed the atmosphere, ocean and land," the report reads. "Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred."

The UN panel said there is more evidence than ever before that human activity and greenhouse gas emissions are warming the planet at a rate unprecedented in the last 2,000 years and that the impacts of that warming are already severe and widespread.

"Human-induced climate change is already affecting many weather and climate extremes in every region across the globe," according to the report.

"Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and their attribution to human influence, has strengthened" since the last UN climate science report in 2013.

The report from the Intergovernmental Panel on Climate Change (IPCC) was compiled by 234 authors from 66 different countries who analyzed more than 14,000 scientific reports about climate change. It will set the stage for global negotiations later this year on how to more drastically reduce greenhouse gas emissions to limit the impact of warming temperatures as much as possible.

John Kerry, the special presidential envoy for climate, said the report underscores the "overwhelming urgency" and high stakes for those international talks.

"The world must come together before the ability to limit global warming to 1.5 degrees Celsius is out of reach. As the IPCC makes plain, the impacts of the climate crisis, from extreme heat to wildfires to intense rainfall and flooding, will only continue to intensify unless we choose another course for ourselves and generations to come. What the world requires now is real action," he said in a statement.

That review confirmed that warming temperatures are contributing to more extreme events in every inhabited part of the world and that if temperatures increase an average of 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, the world will see increasing heat waves, longer warm seasons, and shorter cold seasons. At 2 degrees of warming, the changes will start to reach levels that could threaten human health and agricultural systems in parts of the world.

Global average temperatures have increased between 0.8 degrees and 1.3 degrees Celsius since the industrial age, and climate researchers around the world have ruled out any natural explanation for the rapid rate of increasing temperatures. The report says "some recent hot extremes over the past decade would have been extremely unlikely to occur without human influence on the climate system."

The report finds that global surface temperatures, meaning the temperatures of the oceans and on land, will continue to increase until at least 2050, regardless of actions taken to decrease emissions.

And unless greenhouse gas emissions are drastically reduced, the world will exceed 1.5 degrees of warming in the next 20 years. Limiting future warming to 2 degrees Celsius will require "immediate, rapid and large-scale reductions in greenhouse gas emissions," according to the IPCC.

Ko Barrett, a vice chair for the UN climate panel and senior adviser for climate at the National Oceanic and Atmospheric Administration, said that even though the world's current path is likely to meet or exceed the amount of warming targeted in the Paris Agreement there is still a chance to limit the amount of warming and limit the impacts of climate change.

"It's true that unless there are immediate rapid and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5 degrees Celsius will be beyond reach. But there are pathways that take us to keep these levels in check. It just requires strong rapid and sustained reductions in CO2 (carbon dioxide), methane and other greenhouse gases," she told ABC News.

Barrett said that even with the sobering findings of the report, she's seen a stronger reaction from governments and young people throughout the world who want to prevent the worst-case scenarios.

"At the same time that it's, you know, undeniable that these -- some of these findings are dire. There also is, at least in my mind, a real sense of hope and a drive for action," she said.

While drastic emissions reductions could stabilize rising temperatures and prevent more dire consequences from additional warming, the UN panel found that some impacts of climate change to the oceans and ice in the Arctic are locked in for years to come, while the amount of emissions will determine how rapidly those impacts accelerate.

The report found that oceans will continue to warm, become more acidic and contain less oxygen for the rest of the 21st Century -- though those impacts can still be made less severe if we reduce greenhouse gas emissions.

Glaciers and permafrost are also almost certain to continue melting for decades -- or even centuries -- and the report says the Arctic may "practically" be ice free in September near the middle of the century under certain greenhouse gas scenarios. September is when we usually see the minimum sea-ice coverage in the Arctic.

"If we were to stop emitting greenhouse gases today the planet would stop warming, but sea level would continue to rise. However, I think it's important to manage that our emissions matter hugely for the long-term amount of sea level rise and how quickly it comes," Bob Kopp, an author of the report and director of the Rutgers Institute of Earth, Ocean & Atmospheric Sciences, told reporters on Sunday.

The report found that global mean sea level has already risen by .656 feet between 1901 and 2018 and will continue to rise at least through 2100.

"In the longer term, sea level is committed to rise for centuries to millennia due to continuing deep ocean warming and ice sheet melt and will remain elevated for thousands of years," the report says.

While the report lays out some dire impacts of climate change it's also a call to action for reducing greenhouse gas emissions as soon as possible to prevent some of these worst-case scenarios and limit these impacts as much as possible.

"Stabilizing the climate will require strong, rapid and sustained reductions in greenhouse gas emissions, and reaching net-zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate," said IPCC Working Group I Co-Chair Panmao Zhai.

The IPCC is expected to release two more reports on adapting to the impacts of climate change and possible policy solutions to limit warming and meeting the goals of the Paris Agreement in early 2022.

ABC News' Dan Manzo contributed to this report.