North American ice sheets drove dramatic sea-level rise at the end of the last ice age

Tulane University

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Midnight view of the Greenland Ice Sheet near Ilulissat in July 1991. The background shows the vast ice sheet, while the foreground fjord is choked with icebergs released by one of the world’s fastest-moving outlet glaciers. During the last ice age, this ice sheet was directly connected to the ice masses that covered most of Canada. (Photo by Torbjörn Törnqvist) 

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Credit: Photo by Torbjörn Törnqvist/Tulane University

Melting ice sheets in North America played a far greater role in driving global sea-level rise at the end of the last ice age than scientists had thought, according to a Tulane University-led study published in Nature Geoscience.

The findings overturn decades of conventional wisdom about how Earth emerged from its last great freeze and could reshape how scientists view the risks of climate change in today’s warming world.

Between 8,000 and 9,000 years ago, retreating North American ice sheets alone caused more than 30 feet (about 10 meters) of global sea-level rise. For years, scientists assumed Antarctica was a more important contributor during this period, but the new study shows the opposite: Antarctica’s role was comparatively small, while North America’s ice masses were the dominant driver. 

“This requires a major revision of the ice melt history during this critical time interval,” said Torbjörn Törnqvist, Vokes Geology Professor at Tulane and co-author of the study. “The amount of freshwater that entered the North Atlantic Ocean was much larger than previously believed, which has several implications.” 

The North Atlantic is one of the most sensitive parts of the global climate system, powering ocean currents such as the Gulf Stream that keep the weather in Northwest Europe much milder than it would be otherwise. Decades of research have shown that those currents can weaken due to the influx of freshwater, for example from Greenland’s melting ice. This would not only lead to dramatic cooling in Europe but could also change rainfall patterns in the Amazon. 

The Tulane findings suggest the system was surprisingly resilient in the past, which differs from recent studies that have concluded that a weakening or even a collapse of the Gulf Stream is imminent  

“Clearly, we don’t fully understand yet what drives this key component of the climate system,” Törnqvist said. 

Reconstructing past sea levels from more than 8,000 years ago is notoriously difficult because it often requires offshore drilling. A breakthrough came when former Tulane postdoc Lael Vetter discovered deeply buried ancient marsh sediments preserved just across the Mississippi River from New Orleans. Carbon-14 dating of those samples pushed the sea-level reconstruction back to more than 10,000 years. 

Building on that work, former PhD student Udita Mukherjee combined the Mississippi Delta record with data from Europe and Southeast Asia. The global comparison revealed striking differences in sea-level rise rates — differences that only a much larger North American ice melt could explain. 

“This research provides a stark reminder of the complexities of our climate system and melting ice sheets,” said Mukherjee, now a postdoctoral fellow at the University of Hong Kong. “Broadening our focus beyond North America and Europe to include valuable high-quality data from Southeast Asia was critical for this study. By embracing a truly global perspective in climate studies, we can enhance our understanding and work together towards a sustainable future.” 

The research was funded by the U.S. National Science Foundation and co-authored by colleagues from the University of Ottawa and Memorial University in Canada, Maynooth University in Ireland and the University of South Florida. 

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Journal

Nature Geoscience

DOI

10.1038/s41561-025-01806-0 

Article Title

Sea-level rise at the end of the last deglaciation dominated by North American ice sheets

Article Publication Date

9-Oct-2025

 

Early planting to avoid heat doesn’t match current spring wheat production

Washington State University

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Wheat growing in Eastern Washington.

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Credit: Photo Scott Weybright/Washington State University.

PULLMAN, Wash. — Planting wheat earlier in the spring to avoid crop damage from ever-hotter summers may not keep harvests on pace with current levels.

That’s a key finding from new research at Washington State University challenging assumptions that earlier planting could offset the effects of a warming climate. Researchers used computer modeling to show that moving crop plantings earlier in the season brings about other plant growth issues that could hinder productivity.

The findings were published in Communications, Earth, and Environment.

“Over the years, a lot of studies addressing climate change in agriculture have talked in positive terms about earlier planting as a fix for increased heat,” said Kirti Rajagopalan, an assistant professor in WSU’s Department of Biological Systems Engineering. “We wanted to look at that more critically because it seemed very simplified. We thought the reality could be more nuanced, and that is reflected in our findings.”

Rajagopalan and her graduate student, Supriya Savalkar, are the lead authors on the paper. They studied spring wheat across much of the northern U.S., working with other scientists, including wheat breeders, to analyze planting windows and temperatures in the various regions. The team used high-performance computing power to run simulations in every region.

Their data clearly showed that spring wheat could have less productivity than current levels even if the crop is fully grown before the height of summer temperatures.

“Yes, earlier planting has some benefits,” Rajagopalan said. “But we wanted to make sure we haven’t overemphasized those benefits compared to potential tradeoffs.”

Early planting can still, despite a changing climate, expose crops to less than ideal temperatures in other growth stages, which could limit growth.

“We looked at how the crops experience temperature ranges,” said Savalkar, who will defend her PhD dissertation in November. “You can reduce heat stress in some stages, but at the cost of exposing it to elevated heat or cold stress in other growth stages.”

Another impact of earlier planting is a reduction in the planting window. The USDA provides current planting windows for crops by region, and spring wheat currently has a window of around 11 weeks. Earlier planting may shrink that window down to one to seven weeks, Savalkar said.

“Shrinking the planting window is a nightmare for farmers,” Rajagopalan said. “It’s already challenging for them to get all their crop in the ground; having less time would be much harder.”

The study could have an impact on other facets of the agriculture industry, including wheat breeding. Mike Pumphrey, WSU’s O.A. Vogel Chair of Spring Wheat Breeding and Genetics and a co-author on the paper, said it shows a need for wheat varieties that mature earlier while still producing high yields.

“We had no idea what the results of this study would be because nobody has really looked this in depth at the impact of early planting,” said Pumphrey, a professor in WSU’s Department of Crop and Soil Sciences. “Wheat has been produced from average conditions for over 100 years. Now, conditions are changing so significantly in such a short period of time that it’s hard to adjust.”

The paper only covered spring wheat generally and did not look at specific varieties. It did include one finding that may be helpful for growers in Washington. The only region that showed the potential for similar crop productivity between early planting and normal planting was the Pacific Northwest.

“Other spring wheat regions face more heat or cold stress,” Rajagopalan said. “Plants have a range of temperatures that work well for them, and most parts of the country are on the edges of those ranges. The Pacific Northwest has more leeway on that.”

The paper does not say early planting is all negative, it only points out some of the potential risks. Rajagopalan and Savalkar both hope to see more work done to help growers keep producing crops in a changing environment.

“Earlier planting is something that should and will be considered,” Savalkar said. “But there’s a lot of work to be done to make sure farmers can continue, or even increase, their production.”

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-025-02716-0 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

Earlier planting fails to replicate historical production conditions for US spring wheat under future climates

 

Shedding light on the impact of the Bank of Japan’s exchange-traded fund purchase program

Researchers investigate the role of passive investors in the equity lending market in this study

Waseda University

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Researchers reveal the consequent tug-of-war between monetary policy and market participants in the lending market.

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Credit: Associate Professor Junnosuke Shino from Waseda University, Japan

It is widely recognized that the Bank of Japan’s Exchange-Traded Fund (ETF) purchases had a substantial impact on stock prices. Market participants and media reports have often highlighted that the policy distorted market valuations. At the same time, they pointed out that ETF management appeared to accelerate stock lending activity as the number of ETFs held by the Bank of Japan increased over time. This pattern suggests that the stock market, particularly the lending market, has mechanisms that enhance market efficiency and counteract the effects of the Bank of Japan’s policy.

Recently, a team of researchers from Japan, led by Dr. Junnosuke Shino, Associate Professor at the Faculty of International Research and Education, Waseda University, along with Dr. Mitsuru Katagiri from the Faculty of Commerce, Waseda University, and Dr. Koji Takahashi from the Institute for Monetary and Economic Studies, Bank of Japan, has shed new light on this tug-of-war between monetary policy and market participants in the lending market. Their findings were made available online and published in The Review of Asset Pricing Studies on 04 September 2025.

The key finding of this study is that the Bank of Japan’s large-scale purchases of ETFs in recent years have not only directly pushed up stock prices in the equity market but have also had a significant impact on the securities lending market, where stocks are borrowed and lent for activities, such as short selling.

“While previous studies have focused on the price-boosting effects of the policy, our research reveals a mechanism whereby increased ETF purchases by the Bank of Japan lead to a greater supply of stocks in the securities lending market, making short selling easier and thereby weakening the initial price-boosting effect of the Bank of Japan’s purchases,” explain the researchers.

This is a novel finding, indicating that through ETFs—which have rapidly gained prominence worldwide in recent years—the equity and securities lending markets are interlinked and jointly influence stock prices.

Notably, this study is based on actual data from the stock market, making the findings directly relevant to the real world. In particular, it suggests that the stock market functions efficiently to some extent. In other words, although an investor may aim to constrain stock supply in the spot market to push up prices through large-scale purchases, the stock lending market acts as a mechanism that helps mitigate distortions in stock prices.

They highlighted, “Our work is important in that it reveals how central bank asset purchase policies can influence financial markets and asset prices not only through direct channels, but also via a variety of indirect mechanisms. This highlights the need to assess the impact of such policies from a broader perspective when designing future asset purchase programs or financial market systems. In particular, given that the Bank of Japan still holds tens of trillions of yen worth of ETFs, the study provides a valuable viewpoint for considering the potential effects that may arise as the Bank gradually unwinds these holdings in the future.”

Furthermore, the findings of this research are valuable for foreign central banks and international institutions as well. Japan’s unprecedented experience of large-scale purchases of equity index-linked ETFs by a central bank could serve as a reference point for future policy decisions. For investors and market participants, understanding the impact of ETFs on the securities lending market also offers useful insights for asset management and risk control.

In this way, the present study offers not only academic contributions but also practical implications that can support decision-making in policy implementation and market activities.

 

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Reference
DOI: 10.1093/rapstu/raaf008

 

 

Authors: Mitsuru Katagiri1, Junnosuke Shino1, and Koji Takahashi2

 

Affiliations:

1Waseda University, Japan

2Bank of Japan, Japan

 

About Waseda University
Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including eight prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015. 

To learn more about Waseda University, visit https://www.waseda.jp/top/en  

 

About the Authors
Dr. Mitsuru Katagiri is an Associate Professor in the Faculty of Commerce at Waseda University, Japan. He earned his Ph.D. in Economics from the University of Pennsylvania, U.S., in 2011.

Dr. Junnosuke Shino is an Associate Professor in the Faculty of International Research and Education at Waseda University, Japan. He received his Ph.D. from Rutgers University, U.S., in 2011.

Mr. Koji Takahashi is a Senior Economist and Head of the Economic Studies Group at the Institute for Monetary and Economic Studies, Bank of Japan. He obtained his Ph.D. in Economics from the University of California, San Diego, U.S., in 2017.

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Journal

The Review of Asset Pricing Studies

DOI

10.1093/rapstu/raaf008 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

To Lend or Not to Lend: The Bank of Japan’s ETF Purchase Program and Securities Lending