Quotes from Experts

New IPCC report: Quotes from authors

On August 9, 2021, the Intergovernmental Panel on Climate Change (IPCC) released the first working group section of its latest report, AR6 Climate Change 2021: The Physical Science Basis. We asked the following questions to several co-authors of the report. Reporters can use the video clips, audio, and comments below in news stories, with attribution to the scientist who made them.

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August 9, 2021


What is the most important take-home message you’d like Americans to hear as this report gets released?


Dr. Kim Cobb

“There’s really one key message that emerges from this report: We are out of time. And this report really provides compelling, scientific linkages between the headlines that we see today and what we know about the physics of the climate system and how it’s being impacted by rising greenhouse gases.”
(Posted August 9, 2021 | Download Video)

Kim Cobb, Ph.D.
Professor of earth and atmospheric sciences, Georgia Institute of Technology (she/her)

Dr. Baylor Fox-Kemper

“The biggest, most important aspects of climate change are not changing from report to report. And so things like the fact that the earth—were we to double the amount of carbon in the atmosphere—would warm by about 5 degrees Fahrenheit doesn’t change in this report. But the precision with which we can say that has improved, and in particular regional information, and information about extremes is provided in this report at a level of detail that exceeds any of the previous reports.”
(Posted August 9, 2021 | Download Video)

Baylor Fox-Kemper, Ph.D.
Professor of earth, environmental, and planetary sciences, Brown University (he/him)

Dr. Jessica Tierney

“So we keep hearing more and more in the news about these extreme events, and the takeaway message from this new report is that these events are just going to occur more and more often as global temperatures rise. And they may get more and more intense. And so in the Western U.S., for example, we need to think hard about issues like water conservation and water storage in order to sort of weather through these increasingly extreme events.”
(Posted August 9, 2021 | Download Video)

Jessica Tierney, Ph.D.
Associate professor of geosciences, University of Arizona (she/her)

Dr. Linda O. Mearns

“I used to say, when I was talking about climate change, that climate change is serious, certain, and soon. But this is no longer accurate. Now it is very serious, very certain, and now.”
(Posted August 9, 2021 | Download Video)

Linda O. Mearns, Ph.D.
Senior scientist, Research Applications Lab, National Center for Atmospheric Research (she/her)

“The changes that we have seen so far are associated with around 1 degree C of warming. Limiting warming to the 1.5 degree C target of the Paris Agreement would require immediate, rapid, and large-scale reduction in greenhouse gas emissions.  However, regardless of any specific temperature target, every degree matters: Reducing emissions will reduce impacts.”
(Posted August 9, 2021)

Mathew Barlow, Ph.D.
Professor of climate science, University of Massachusetts Lowell

What does the new IPCC report tell us about attributing extreme weather-related events in the United States to human-caused climate change?


Dr. Jessica Tierney

“OK, so this is a major change from the last IPCC report which came out eight years ago. Eight years ago we weren’t completely sure whether some of the extreme events we’re seeing were due to human-caused climate change. Now we’re pretty sure that that is the case. So some examples might be the extreme heat waves that we’re seeing around North America right now. The IPCC, this new report, says that those heat waves were unlikely to occur without human climate change.”
(Posted August 9, 2021 | Download Video)

Jessica Tierney, Ph.D.
Associate professor of geosciences, University of Arizona (she/her)

Dr. Kim Cobb

“Not surprisingly, the IPCC report brings new links, and stronger links, between any number of different weather and climate extremes and rising greenhouse gases and global warming. Most notably, extreme precipitation is on the rise, as are wildfires and droughts, and of course gripping headlines across the world right now, heat extremes across the land and the ocean.”
(Posted August 9, 2021 | Download Video)

Kim Cobb, Ph.D.
Professor of earth and atmospheric sciences, Georgia Institute of Technology (she/her)

Dr. Baylor Fox-Kemper

“Climate change is something that takes place over decades and centuries. And so when we think about the changing weather, it’s really the repeat occurrences or the tendencies of weather events that are changing over decades. Even so, because of past emissions, we’re already seeing changes to weather in North America, like a drier southwest, a wetter northeast, and a longer fire season, a more intense fire season, and all of those changes are expected to deepen as we go farther into this century.”
(Posted August 9, 2021 | Download Video)

Baylor Fox-Kemper, Ph.D.
Professor of earth, environmental, and planetary sciences, Brown University (he/him)

“There’s much more attention to the attribution of extreme events in this report. And this includes a number of different types of extremes, for example, intensification of extreme precipitation, extreme temperatures, and some attribution of individual events, for example hurricanes, for example Hurricane Harvey.”
(Posted August 9, 2021)

Linda O. Mearns, Ph.D.
Senior scientist, Research Applications Lab, National Center for Atmospheric Research (she/her)

“In general, the attribution of extreme weather events to human-caused climate change can now be made with higher certainty, and we now have increased evidence that extreme events are becoming both more frequent and more severe. Human influence very likely contributed to the observed increase in heatwaves and likely contributed to the increased intensity of heavy rainfall. Increases in weather conditions favorable to fire (“fire weather”) and some aspects of drought in the Western U.S. have also been linked to human-caused climate change.

For the future, we expect a continued increase in the intensity and frequency of extreme events, with larger increases for higher greenhouse gas emissions. The increases observed so far have occurred with around 1 degree C of warming. Reducing emissions will reduce impacts; limiting warming to the 1.5 degree C target of the Paris Agreement would require immediate, rapid, and large-scale reduction in greenhouse gas emissions.”
(Posted August 9, 2021)

Mathew Barlow, Ph.D.
Professor of climate science, University of Massachusetts Lowell

What does the new IPCC report tell us about anticipated long-term climate changes in the United States (e.g. droughts, changes in snow cover)?


Dr. Kim Cobb

“The IPCC report makes clear that the United States, like many other countries, is facing a host of climate change challenges going forward. These range from rising sea levels along our coastlines to changes in water resources that are linked to changes in their water cycle, including extreme precipitation. And of course, the threat of heatwaves, wildfires, and droughts are also going to be increased going forward.”
(Posted August 9, 2021 | Download Video)

Kim Cobb, Ph.D.
Professor of earth and atmospheric sciences, Georgia Institute of Technology (she/her)

Dr. Jessica Tierney

“Snowpack in the Western United States is almost certain to decline in the future. And that has implications for water availability, because a lot of the stream flow in the Western United States, for example the Colorado River, depends on snow. So we have increased confidence that we’re going to see less flow through our river systems in the Western U.S., which means that we’re going to be even more prone to drought. And in fact, if emissions continue, then there is a very good chance that we’re going to see a level of drought and aridity that we haven’t seen in at least a thousand years.”
(Posted August 9, 2021 | Download Video)

Jessica Tierney, Ph.D.
Associate professor of geosciences, University of Arizona (she/her)

“My role in the IPCC is a chapter that was focused on sea level rise, as well as changes in the ocean and frozen parts of the earth. And sea level rise is one of the most important, slow-moving processes, or slow-moving impacts of climate change. And so, as we get toward the end of this century, if we have low emissions, we expect to see something like one to two feet of sea level rise and something higher like two to three feet under high emissions. But in fact, if certain changes in Antarctica occur, we could see as much as six feet—or it’s really as much as six feet can’t be ruled out as a possibility.”
(Posted August 9, 2021)

Baylor Fox-Kemper, Ph.D.
Professor of earth, environmental, and planetary Sciences, Brown University (he/him)

“Projections of the future U.S. climate show changes to a wide range of important aspects, including to heatwaves, heavy rainfall, drought, snow, the seasonal cycle, sea level rise, and ocean acidification. Heatwaves and the intensity of heavy rainfall are projected to continue increasing, and snow decreasing, for most of the U.S.; and the occurrence of drought and weather conditions favorable to wildfires are projected to continue increasing for the Western U.S. Of importance to coastal communities and ecosystems, ocean temperature, ocean acidity, and sea levels are all projected to continue increasing. Higher emissions will lead to larger changes; reducing emissions will reduce the severity of the impacts.

The general aspects of heatwaves and heavy rainfall are primarily considered in Chapter 11; the variability and seasonality of rain and the water cycle in Chapter 8; drought in Chapters 8 and 11; snow in Chapters 8 and 9; and sea level rise and ocean acidification in Chapter 9. More regionally-specific information is provided in Chapters 11, 12, and the Atlas.”
(Posted August 9, 2021)

Mathew Barlow, Ph.D.
Professor of climate science, University of Massachusetts Lowell

Is there anything else reporters should know as they dig into this report?


Dr. Kim Cobb

“I think one of the most valuable things about this report is that it provides a rich framework for assessing regional impacts of ongoing climate changes. And we can do that a lot better in this round than we could in previous reports. And so that provides really a tapestry to bring to life what specific regions may be facing going forward and of course what communities can do to keep themselves safe.”
(Posted August 9, 2021 | Download Video)

Kim Cobb, Ph.D.
Professor of earth and atmospheric sciences, Georgia Institute of Technology (she/her)

Dr. Baylor Fox-Kemper

“Climate change is a global problem. And one of the things about global problems that’s important to remember is that we should be working together as scientists and governments from around the world. And so one exciting aspect about this report is that there’s actually open data access, and people can go on their own to what’s called the interactive atlas and see what the changes will be like in their region.”
(Posted August 9, 2021 | Download Video)

Baylor Fox-Kemper, Ph.D.
Professor of earth, environmental, and planetary sciences, Brown University (he/him)

“There are now chapters that focus more deeply on extreme events, specifically on climate impact drivers—conditions that lead to important impacts. And there’s also an impressive interactive atlas where reporters and people can explore many results for themselves.”
(Posted August 9, 2021)

Linda O. Mearns, Ph.D.
Senior scientist, Research Applications Lab, National Center for Atmospheric Research (she/her)

“The new IPCC report projects that sea level is likely to rise by a little less than a foot by 2050, so that’s only thirty years away, regardless of the emissions scenario around how much we emit. And that’s because we already have a lot of ice melting that’s coming in the pipeline, contributing to sea level. Now in terms of the end of the century, it could be anywhere from about a foot and a half to three feet of sea level rise depending on how much we emit. So this is obviously important for all of our cities that are sitting very close to the coast line such as on the Eastern Seaboard, Florida, Gulf Coast.”
(Posted August 9, 2021)

Jessica Tierney, Ph.D.
Associate professor of geosciences, University of Arizona (she/her)

“Solar Radiation Management (SRM), the idea of limiting global warming by reducing the amount of sunlight reaching Earth’s surface, has begun to receive a lot of attention. The report shows that while SRM could potentially offset some effects of global warming, there would likely be substantial regional and seasonal trade-offs as the effects of SRM are not uniform; rapid implementation or termination of SRM could cause abrupt changes to the water cycle; and SRM does not address some important effects of climate change such as ocean acidification. SRM is considered in the Technical Summary, Box TS.8; and in Chapters 4, 5, 6, and 8.

Finally, one last thing to keep in mind is that this report is based on a careful assessment of a very large body of peer-reviewed scientific evidence:  More than 200 scientists from over 60 countries reviewed more than 14,000 peer-reviewed scientific papers.”

Mathew Barlow, Ph.D.
Professor of climate science, University of Massachusetts Lowell

Creative Commons LicenseThe text and video on this page are licensed as Creative Commons CC BY-SA 4.0. Journalists are free to use any text or video on this page with or without attribution to SciLine.

Dr. Mathew Barlow, Ph.D., professor of climate science, University of Massachusetts Lowell

None provided

Dr. Kim Cobb, Ph.D., professor of earth and atmospheric sciences, Georgia Institute of Technology (she/her)

I have no conflicts to declare.

Dr. Baylor Fox-Kemper, Ph.D., professor of earth, environmental, and planetary sciences, Brown University (he/him)

Prof. Fox-Kemper is an oceanographer and climate modeler who seeks to improve the representation of small-scale processes in climate models. Past and present funding support from federal and state agencies, universities, the Schmidt Futures Foundation, and the Gulf of Mexico Research Initiative are gratefully acknowledged.

Dr. Linda O. Mearns, Ph.D., senior scientist, Research Applications Lab, National Center for Atmospheric Research (she/her)

Dr. Mearns is a climate scientist working on regional climate change, climate change scenario formation, and exploring uncertainties in climate change. No funding for these research areas is received from for-profit entities. She has no conflicts of interest.

Dr. Jessica Tierney, Ph.D., associate professor of geosciences, University of Arizona (she/her)

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