The Intergovernmental Panel on Climate change (IPCC) has just released its latest major assessment report on global climate change, approved by the world’s governments.
Climate Change 2021: Physical Science Basis is the Working Group I contribution to the IPCC’s Sixth Assessment Report (AR6). The Working Group comprises more than 200 scientists from 66 countries who assessed the current scientific understanding of climate change. Northern Arizona University Regents’ Professor Darrell Kaufman of the School of Earth and Sustainability is a lead author of the report, which will form the scientific underpinnings for negotiations with governments later this year to limit global carbon emissions.
The IPCC report is the world’s most comprehensive and authoritative source of scientific information on understanding and responding to climate change. The report is based on a review of many thousands of scientific papers and is scrutinized by hundreds of scientists from around the world. Since the Fifth Assessment Report was published in 2013, new evidence shows how much humans are influencing the climate system, and how society’s actions to limit greenhouse gas emissions will determine the future of Earth’s climate.
“The contributions of Dr. Kaufman and his team to the IPCC’s Sixth Assessment Report, which is being played out on the world’s stage, speak to NAU’s stature as a research university as well as to the prominence of each of these individual scientists. As we continue to build on our strong legacy of environmental and climate science research, our paleoclimatologists have again proven that the value of this work lies in its global impact on public policy—ultimately affecting the quality of life for all,” NAU President José Luis Cruz Rivera said.
Kaufman is a lead author on the chapter, “The changing state of the climate system,” which features information about natural climate variability over a wide range of time scales. “My role in the new report focused on changes in the climate system prior to industrialization, or ‘paleoclimate’, as context for understanding what’s happening now and what could happen in the future,” Kaufman said.
He also co-authored the report’s FAQs and summary documents, including the “Summary for policy makers,” which was subjected to an intense line-by-line approval process involving dialogue between the authors and delegates from more than 100 countries. “It was a lot of work, but super gratifying to have the opportunity to carry it through to the approval step. That’s where authors and governments collaborated to craft a summary that’s timely and most helpful for policy decisions.”
The IPCC represents the world’s scientific community by periodically reporting on the state of knowledge about climate change, following an extensive and transparent review process by experts and governments around the world to independently assess all published information and to summarize the most relevant advances in climate science.
Recent publications by Kaufman and other NAU paleoclimate scientists were featured prominently in the report. The paleoclimate team includes professor R. Scott Anderson, associate professor Nicholas McKay, assistant professor of practice John Fegyveresi and assistant research professors Michael Erb and Cody Routson, as well as their postdoctoral researchers, graduate and undergraduate students. They study how the climate system changes on time scales of decades to many thousands of years, as it responds to both natural and human-caused forcings.
“Understanding environmental change and its current trajectory requires a long-term perspective of the natural variability in the Earth system,” he said. “We conduct our field-oriented research in Arizona, Colorado, Alaska, Antarctica and New Zealand. In the lab, we analyze a variety of biological and physical properties of sediment cores that we collect from lakes, and ice cores from polar ice sheets. And in collaboration with our colleagues worldwide, we are developing major global datasets of long-term climate to better quantify past changes and to compare them with the output of Earth system models.
Key NAU studies inform IPCC assessment
Several major NAU research projects, funded chiefly through grants from the National Science Foundation, have been aimed at understanding the causes and effects of natural climate variability. The scientists’ recent work clarifies how unusual recent global warming has been compared to natural climate fluctuations of the past.
Evidence from warmer periods that occurred prior to industrialization, generated by NAU studies, was also used in the report to clarify how climate change will play out over multiple centuries and millennia, as polar ice, deep ocean circulation and other slow-moving features of the climate system adjust to a warmer world.
Key NAU studies that contributed to the upcoming IPCC report include the following:
- Over the past 150 years, global warming has more than undone the global cooling that occurred over the past six millennia, according to a major study published in 2020 in Nature Research’s Scientific Data. The findings show that the millennial-scale global cooling began approximately 6,500 years ago when the long-term average global temperature topped out at around 0.7°C warmer than the mid-19th century. Since then, accelerating greenhouse gas emissions have contributed to global average temperatures that are now surpassing 1°C above the mid-19th century. Kaufman led this study, with McKay as co-author, along with collaborators Routson and Erb. The team worked with scientists from research institutions all over the world to reconstruct the global average temperature over the Holocene Epoch—the period following the Ice Age and beginning about 12,000 years ago. (See related story.)
- In 2020, NAU doctoral candidate Ellie Broadman led a study published in the journal Proceedings of the National Academy of Sciences. Working with Kaufman and four noted British scientists, Broadman and the team compiled a new record of hydroclimatic change in the past 10,000 years in Arctic Alaska, revealing that periods of reduced sea ice result in isotopically heavier precipitation derived from proximal Arctic moisture sources. The researchers supported their findings about this systematic relationship through isotope-enabled model simulations and a compilation of regional paleoclimate records. (See related story.)
- Also in 2020, an international group of 93 paleoclimate scientists from 23 countries—led by Kaufman, McKay, Routson and Erb—publisheda set of records in Scientific Data representing the most comprehensive paleoclimate data ever compiled for the past 12,000 years, compressing 1,319 data records based on samples taken from 679 sites globally. At each site, researchers analyzed ecological, geochemical and biophysical evidence from both marine and terrestrial archives, such as lake deposits, marine sediments, peat and glacier ice, to infer past temperature changes. Countless scientists working around the world over many decades conducted the basic research contributing to the global database.
- In 2019, Routson led the paleoclimate team in a study published in Nature using climate records dating back thousands of years to demonstrate that warming in the Arctic is associated with fewer storms and increased aridity in a huge swath of the Northern Hemisphere, including most of the continental United States. The scientists showed that this pattern could lead to dramatic effects on agriculture and population centers throughout the U.S., Europe and Asia. (See related story.)
- According to a 2016 study, global warming began in the Arctic and tropical oceans before thermometers were widespread enough to record the early signal. Kaufman and McKay, along with scientists from around the world, discovered that human-caused global warming began in the mid-1800s. The NAU scientists, who co-authored the study published in Nature, examined the climate variation found in corals, ice cores, tree rings and the changing chemistry of stalagmites in caves worldwide. (See related story.)
Several other NAU scientists have served on IPCC working groups and/or contributed research to previous IPCC reports as well, including Regents’ Professor Scott Goetz, professor Kevin Gurney, Regents’ Professor Bruce Hungate, Regents’ Professor Yiqi Luo, Regents’ Professor Michelle Mack, assistant research professor Christina Schädel and Regents’ Professor Ted Schuur. All NAU scientists’ efforts for the IPCC are voluntary.