U.N. panel paints grim future for humanity without drastic action to combat climate change

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• William Brangham:

  A dire warning and a stark reality. Global temperatures will rise. It is unequivocal that human activity is driving the surge. The extremes we're now experiencing — fires, floods, droughts, and storms, will only intensify. That is all part of a landmark report by a team of more than 230 scientists convened by the U.N.'s Intergovernmental Panel on Climate Change.

• William Brangham:

  The western U.S. is sifting through the ashes of yet another catastrophic fire season; one that's only just begun. And, today, climate scientists at the United Nations made it clear: these extreme events are largely our doing.

  This independent report released by the U.N. is the starkest warning yet that the planet is warming to a dangerous degree. It affirms that our burning of coal, oil and gas is accelerating climate change, and that climate change is behind many of these extreme weather events.

  The authors say these effects are happening far faster than predicted.

  Kim Cobb, Georgia Institute of Technology: There's really one key message that emerges from this report: we are out of time.

• William Brangham:

  The 3,000-page report is the work of more than 200 scientists from around the world. They found that global temperatures are the hottest in 100,000 years, and many effects of climate change are already irreversible.

  Those temperatures are on track to pass the target set by the 2015 Paris Climate agreement, and pass them decades earlier than expected.

  The report says that if the planet warms beyond the target of 1.5 Celsius, or 2.7 degrees Fahrenheit, these extreme weather events are forecast to be more frequent, and more severe. The report states that only by drastically cutting greenhouse gas emissions can these extremes be lessened.

• Ko Barrett, Vice Chair, IPCC:

  Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5 degrees C or 2.7 degrees Fahrenheit will be beyond reach.

• William Brangham:

  Scientists say the consequences of climate change are ever present, from the severity of the wildfires and droughts in the Western U.S. to devastating flooding across Europe just last month.

  World leaders are set to assess today's report, and plot their response, at the next global climate summit in Scotland this November.

• William Brangham:

  For a closer look at today's report and the science behind it, we turn again to Michael Oppenheimer. He's a professor of geosciences and international affairs at Princeton University. And while not an author of this latest report, he is a long-time participant in the work of the Intergovernmental Panel on Climate Change.

  Michael Oppenheimer, always Michael Oppenheimer, always great to you have on the NewsHour.

  The head of the U.N. referred to this as code red for humanity. Do you share that dire assessment?

• Michael Oppenheimer:

  Unfortunately, I do. The forecast is really grim. The climate is changing at an accelerating pace and that means basically we're in trouble. More intense heat waves, heavier precipitation during extreme rainstorms, draught, hurricanes shifting to more category four and five.

  The longer we wait to reduce the emissions of the green house gases like carbon dioxide that are causing the problem, the worse it's going to get.

• William Brangham:

  One thing that really jumped out to me in this report is the attribution science, directly connecting climate change to specific events. That seems to be getting particularly sharp, are we getting better and better at making those linkages?

• Michael Oppenheimer:

  Oh, much better. I mean even 15, 20 years ago, we really couldn't make specific statements about specific events. And we declared that as the case.

  We would make general statements about what's the global trend, for instance. Now rather than big general statements about the havoc that climate change is causing we can make very specific statements about what has happened in particular events at particular places and particular times.

  We can say how much climate change increased the chances of an individual damaging or deadly event having occurred in the first place. That would be, for instance, the intense rainfall that occurred in 2017 and Hurricane Harvey that was about 50 percent or more what it usually would be without the green house gases in the atmosphere. It would be like the cause of the Australian fires where we could say — wildfires two years ago, where we could say specifically what is the percent that climate change increased the likelihood of that event happening.

  Or it will be done, I'm sure shortly, for the tremendous heat event that occurred in the Pacific Northwest a few weeks ago. That was so off the charts I think it will be relatively easy to say climate change was responsible for a big share of it. We'll see exactly what the data shows as the analysis is done. So that makes climate change real for the average person, and it's no longer a matter of speculation as to whether a bad event that we suffered through was caused by climate change.

  We can say with some precision exactly how much climate change is responsible. That's called attribution.

• William Brangham:

  This report also points out that we have increasingly little time to act.

  Can you talk a little bit about the urgency that the U.N. is putting forward here? Is there a window of time for action that is closing?

• Michael Oppenheimer:

  Well, the general message without large and rapid reductions and emissions of the greenhouse gases, we'll rush into what I call a climate danger zone. That's a warming of greater than about 3 or 4 degrees Fahrenheit, one and a half to two degrees Celsius, that the country agrees to avoid in the 200 — 2015 Paris agreement. In that zone of danger, impacts continually accelerate, compounding and contaminating, beyond society's ability to successfully adapt. That's why countries said we shouldn't go there.

  On the other hand, if it gets serious about rapid immediate reduction and large reductions of the emissions of gases, we could produce a notable slowing of the warming within 20 years, now I don't know and I don't think anybody could say with any sureness whether we're going to make the one and a half or two degree limit, stay out of the danger zone but even if we get out of the danger zone, the quicker we get out of it, the better. So this is not — in the end, this is not a problem that the technological or scientific one. It's a political one, basically.

• William Brangham:

  You pointed out that cutting greenhouse gas emissions is the key here. And we have seen a lot of nations make big pledges, less so big action. President Biden we have seen right now had to trim his very ambitious climate goals in the negotiations in the Congress and Senate.

  Do you have any confidence that the United States let alone all these other nations will actually act in time.

• Michael Oppenheimer:

  Well, let's talk about the there is a wind at the back of the countries that do want to act because we are in the middle of an energy revolution, we are talking about electrifying the whole system including transportation, eventually that electricity can be produced by carbon-free energy. And that will help get us out of the problem. And all of it is, looks like it could be done at a reasonable cost because costs of renewable forking are plummeting.

  Now as I mentioned a second ago, is the political will really going to be there to do that. It is very complicated. You have to make interest groups in a bunch of countries that are the big emitters happy with the serious program to cut emissions.

  I'm not a politician. I can't say whether it will be done. I can say that these countries have moved mountain — moved heaven and earth before on big problems, usually national security.

  This is as big as those problems. They've got to do the same thing again. Whether they will or not — well, it's partly up to us to try to put the pressure on our governments to make them do it.

• William Brangham:

  All right. Michael Oppenheimer from Princeton University, thanks for join us on this very sobering day, always good to see you.

• Michael Oppenheimer:

  Thanks for having me.