UN sounds alarm on 'irreversible' climate impacts, but offers hope

The UN climate panel sounded a dire warning Monday, saying the world is dangerously close to runaway warming and that humans are "unequivocally" to blame.

Already, greenhouse gas levels in the atmosphere are high enough to guarantee climate disruption for decades if not centuries, scientists warn in areportfrom the Intergovernmental Panel on Climate Change (IPCC).

That's on top of the deadly heat waves, powerful hurricanes and other weather extremes that are happening now and are likely to become more severe.

Describing the report as a "code red for humanity," UN Secretary General Antnio Guterres urged an immediate end to coal energy and other high-polluting fossil fuels.

"The alarm bells are deafening," Guterres said in a statement. "This report must sound a death knell for coal and fossil fuels, before they destroy our planet."

WATCH | World reacts to dire forecastfrom UN climate panel:

Climate change affecting every region on Earth, UN report says

3 years ago

Duration 1:20

The UN's Intergovernmental Panel on Climate Change warns in a report that climate disruptions are guaranteed for decades, if not centuries, due to greenhouse gas levels. People of all ages across the world expressed concern for what that means for the future.

The IPCC report comes just three months before a major UN climate conference in Glasgow, Scotland, where nations will be under pressure to pledge ambitious climate action and substantial financing.

Drawing on more than 14,000 scientific studies, the report gives the most comprehensive and detailed picture yet of how climate change is altering the natural world and what still could be ahead.

"This report tells us that recent changes in the climate are widespread, rapid and intensifying, unprecedented in thousands ofyears," said IPCCvice-chair Ko Barrett, senior climate adviser for the U.S. National Oceanic and Atmospheric Administration.

Here are some key takeaways.

World set to cross 1.5 C threshold

Each of five scenarios for the future, based on how much carbon emissions are cut, passes the more stringent of two thresholds setin the 2015 Paris climate agreement.

A rise of 1.5 C above pre-industrial levels is generally seen as the mosthumanitycould cope with without suffering widespread economic and socialupheaval.

Under each scenario, the report said, the world will cross the 1.5 Cwarming mark in the 2030s, earlier than some past predictions. Warming has ramped up in recent years, data shows.

"Our report shows that we need to be prepared for going into that level of warming in the coming decades. But we can avoid further levels of warming by acting on greenhouse gas emissions," said report co-chair Valerie Masson-Delmotte, a climate scientist at France's Laboratory of Climate and Environment Sciences at the University of Paris-Saclay.

In three scenarios, the world will also likely exceed 2Cover pre-industrial times theother, less stringent Paris goal with far worse heat waves,droughts and flood-inducing downpours "unless deep reductions in carbon dioxide and other greenhouse gas emissions occur in thecoming decades," the report said.

WATCH | Greece heat wave worst in 3 decades:

Greece battles wildfires after worst heat wave in 3 decades

3 years ago

Duration 3:50

Wildfires have ignited across Greece in the wake of the nation's most protracted heat wave in 30 years which sent temperatures soaring to 45 C for days creating bone-dry conditions.

Sea level rise, some other harms are irreversible

Some harm from climate change dwindling ice sheets, rising sealevels and changes in the oceans as they lose oxygen and become more acidic is "irreversible for centuries to millennia," the report said.

"We are now committed to some aspects of climate change,some of which are irreversible for hundreds to thousands ofyears,"said IPCC co-author Tamsin Edwards, a climate scientistat King's College London. "But the more we limit warming, themore we can avoid or slow down those changes."

Even if global warming were halted at 1.5 C, theaverage sea level would still rise about twoto threemetres, and maybe more.

Sea level rise has picked up speed, as polar ice sheets meltand warming ocean water expands. Already, associated floodinghas nearly doubled in many coastal areas since the 1960s, withonce-in-a-century coastal surges set to occur once a year by2100.

Scientists could not rule out extreme rises of more than 15metres by 2300, if tipping points trigger runaway warming.

"Themore we push the climate system the greater the odds wecross thresholds that we can only poorly project," said IPCCco-author Bob Kopp, a climate scientist at Rutgers University.

Arctic summers will soon be ice free

Summertime sea ice atop the Arctic Ocean will vanishentirely at least once by 2050, under the IPCC's most optimisticscenario. The region is the fastest-warming area of the globe warming at least twice as fast as the global average.

While Arctic sea ice levels vary throughout the year, theaverage lows during summer have been decreasing since the 1970sand are now at their lowest levels in a thousand years.

Thismelting creates a feedback loop, with reflective ice giving wayto darker water that absorbs solar radiation, causing even morewarming.

WATCH | Some climate change impacts 'irreversible' now, latest IPCC report says:

Some climate change impacts 'irreversible' now, says UN climate panel

3 years ago

Duration 1:16

The world must act to stop climate extremes from getting worse, says a new report by the Intergovernmental Panel on Climate Change.(Maggie MacPherson/CBC)

Good news: worst-case scenario, tipping points unlikely

In five previous reports, the world was on that final hottest path, often nicknamed "business as usual."

But this time, the world is somewhere between the moderate path and the small pollution reductions scenario because of progress to curb climate change, said report co-author Claudia Tebaldi, a scientist at the U.S. Pacific Northwest National Lab.

The report said ultra-catastrophic disasters commonly called "tipping points," like ice sheet collapses and the abrupt slowdown of ocean currents are "low likelihood" but cannot be ruled out.

The much talked-about shutdown of Atlantic ocean currents, which would trigger massive weather shifts, is something that's unlikely to happen in this century, Kopp said.

More than 100 countries have made informal pledges to achieve "net zero" human-caused carbon dioxide emissions sometime around mid-century, which will be a key part of climate negotiations this fall in Scotland. The report said those commitments are essential.

"It is still possible to forestall many of the most dire impacts," Barrett said.

Value of IPCC reports debated

British Prime Minister Boris Johnson said he hoped the report would be "a wake-up call for the world to take actionnow, before we meet in Glasgow."

If it isn't, at least one scientistquestioned whether the IPCC should even continue to issue reports.

"We have all the evidence we need to show we are in a climate crisis," said three-time IPCC co-author Sonia Seneviratne, a climate scientist at ETH Zurich who doubts she will sign up for a fourth report.

"Policy makers have enough information. You can ask: Is it a meaningful use of scientists' time, if nothing is being done?"