Understanding climate change

Understanding climate change Meet the scientists looking backward to help predict the future

BY NOAH HAGGERTY, APPLIED PHYSICS, 2024

In 2014, the United Nations Intergovernmental Panel on Climate Change, the world’s leading voice on the matter, released its latest assessment report, delivering stunning predictions of the potential consequences of human-driven climate change in the 21st century. At the same time that the U.N. panel in Geneva prepared the report for release, an international team of climate and ocean scientists left port — headed for Alaska. They hoped to uncover one of the greatest missing pieces in scientists’ understanding of past climate change: what had happened in the North Pacific directly after the last ice age from 9,000 to 19,000 years ago. The expedition lasted two months, during which the team traveled to five sites to drill sediment cores, which act as geological time capsules, storing information in their chemical make-up. Climate expert and Northeastern professor Dr. Daniel Douglass elaborates, “The transition out of the last ice age is a good chance to study how changes occur.” Furthermore, comparing these results against current climate models, Douglass says, “is the best way to find and correct any mistakes that may exist in the models and gives us more confidence in the accuracy of their predictions going forward.”

In 2020, the analysis of the North Pacific core samples is finally reaching completion in the form of a detailed string of scientific papers. Dr. Alan C. Mix, a climate and ocean researcher at Oregon State University and member of the expedition team, explains, “Each paper builds on the previous one, such that the puzzle picture is starting to emerge, and it appears to be pretty important as one of the ‘missing links’ in global climate evolution.” One of the first pieces of the puzzle was published in 2015 by Dr. Summer In 2014, the United Nations Praetorius, a former student of Mix. Intergovernmental Panel on The paper made headlines announcing Climate Change, the world’s a link between abrupt ocean warming leading voice on the matter, released and expansive oxygen-deficient its latest assessment report, delivering regions, coined “dead zones” because stunning predictions of the potential of their inhospitableness to life. consequences of human-driven climate Praetorius postulated that hotter water, change in the 21st century. At the same which cannot hold as much dissolved time that the U.N. panel in Geneva oxygen as cooler water, accelerates prepared the report for release, an the chemical processes undertaken by international team of climate and small marine lifeforms, like plankton. ocean scientists left port — headed for These processes further remove oxygen Alaska. They hoped to uncover one of from the water by packaging it with the greatest missing pieces in scientists’ organic material, creating a runaway understanding of past climate change: feedback loop in which a small amount what had happened in the North Pacific of ocean warming in a region can cause directly after the last ice age from 9,000 a significant depletion of oxygen. The

“It appears to be pretty important as one of the

‘missing links’ in global climate evolution.”

to 19,000 years ago. The expedition paper warns that ocean temperatures lasted two months, during which in this century are likely to increase at a the team traveled to five sites to drill rate beyond anything measured in the sediment cores, which act as geological past, and the consequences for marine time capsules, storing information life, as well as human fisheries, could in their chemical make-up. Climate be catastrophic. expert and Northeastern professor Dr. Daniel Douglass elaborates, “The Another former student of Mix, Dr. transition out of the last ice age is a Jianghui Du, utilized the expedition’s good chance to study how changes data to add another piece to the puzzle occur.” Furthermore, comparing these in a 2018 paper, linking the release of results against current climate models, carbon dioxide into the atmosphere Douglass says, “is the best way to find to the strength of ocean circulation. and correct any mistakes that may Through computer modeling and exist in the models and gives us more simulation, Du determined that ocean confidence in the accuracy of their currents pulled from a massive carbon predictions going forward.” dioxide reservoir sitting at the bottom of the Pacific and circulated it to the surface, releasing the carbon dioxide into the atmosphere. The model also In 2020, the analysis of the North showed melting glacier water as the Pacific core samples is finally reaching likely culprit of increased circulation, completion in the form of a detailed resulting in yet another climate string of scientific papers. Dr. Alan C. feedback loop where melting glaciers Mix, a climate and ocean researcher at lead to a release of carbon dioxide from Oregon State University and member the ocean, further warming the planet. of the expedition team explains, “Each paper builds on the previous one, such Since the expedition in 2013, an that the puzzle picture is starting to astounding 500 papers detailing the emerge, and it appears to be pretty mechanics of the past North Pacific have important as one of the ‘missing links’ been published based on the expedition’s in global climate evolution.” data. Nearly a decade of work has culminated in two groundbreaking One of the first pieces of the puzzle papers recently published by the team, was published in 2015 by Dr. Summer finally piecing together the story of the Praetorius, a former student of Mix. North Pacific. They determined that the The paper made headlines announcing melting of the Cordilleran Ice Sheet over a link between abrupt ocean warming western Canada and Alaska had caused and expansive oxygen-deficient multiple feedback loops in the Pacific regions, coined “dead zones” because Ocean, triggering a global climate shift. of their inhospitableness to life. The melting had created a cascading Praetorius postulated that hotter water, climate effect that devastated marine which cannot hold as much dissolved ecosystems through the creation of dead oxygen as cooler water, accelerates zones, warmed the Antarctic region, the chemical processes undertaken by contributed to the melting of eastern small marine lifeforms, like plankton. North American ice sheets, and led to a These processes further remove oxygen global increase of atmospheric carbon. from the water by packaging it with The papers solidified the North Pacific organic material, creating a runaway as a key player in both past and future feedback loop in which a small amount global climate events. of ocean warming in a region can cause a significant depletion of oxygen. The The insight these findings provide paper warns that ocean temperatures into modern anthropogenic climate in this century are likely to increase at a change is indispensable. Discussing rate beyond anything measured in the this significance, Mix says, “The past, and the consequences for marine projected scales of [human-driven] life, as well as human fisheries, could change, estimated by models, are far be catastrophic. beyond the range of changes observed in our history... and we now know that Another former student of Mix, Dr. the Pacific is intimately involved in Jianghui Du, utilized the expedition’s rapid global changes.” As the planet data to add another piece to the puzzle continues to warm, Mix hopes to return in a 2018 paper, linking the release of to the North Pacific to study the marine carbon dioxide into the atmosphere geologic record from periods even to the strength of ocean circulation. warmer than where we’re headed.

PHOTO BY SHUTTERSTOCK DESIGN BY KATIE GREEN, BIOENGINEERING, 2022

(2015). DOI: 10.1038/nature15753 Nature

(2020). DOI: 10.1126/science.aba7096 Science