When we think of global warming, what first comes to mind is the air: crushing heatwaves that are felt rather than seen, except through the haziness of humid air. But when it comes to melting ice sheets, rising ocean temperatures may play more of a role - with the worst effects experienced on the other side of the globe.
A new paper in Nature Geoscience, "Spatially variable response of Antarctica's ice sheets to orbital forcing during the Pliocene," explores the complicated dynamics.
While Binghamton University Associate Professor of Earth Sciences Molly Patterson is the first author, the 43 co-authors include several Binghamton alumni, such as Christiana Rosenberg, MS '20; Harold Jones '18; and William Arnuk, PhD '24. The study's results directly address one of the main goals of the International Ocean Drilling Program (IODP) Expedition 374: to identify the sensitivity of the Antarctic ice sheet to Earth's orbital configuration under a variety of climate boundary conditions. Because of this, all shipboard science team members are included as co-authors because of their contributions to the data sets used in the article, Patterson explained.
Their research considers the Antarctic ice sheet during the Late Pliocene period, from 3.3 to 2.6 million years ago. From 3.2 to 2.8 million years ago, the global average temperatures were around 2 to 3° Celsius higher than pre-industrial values, in line with the "middle of the road" scenario for climate change, in which temperatures are expected to rise around 2.7°C by 2100.
"Thus, Pliocene records are considered to be useful analogues for understanding what a future with this level of warming might be like," Patterson explained.
Climate forcing refers to any external factor that causes a change in Earth's energy balance -incoming versus outgoing heat - and ultimately leads to warming or cooling in the Earth system.
Non-human factors that can affect this energy balance include tectonic changes, volcanic eruptions and shifts in the sun's energy output, such as sunspot cycles that happen every 11 years. Another factor is "orbital forcing," or changes in Earth's orbit around the sun; this has typically driven glacial and interglacial cycles, which have lasted around 100,000 years - at least for the last 800,000 years or so.
The non-human factors that affect the Earth's climate occur on different time scales, Patterson said.
"Here we are using geological archives to test how these important components of the climate system respond naturally to warmer climates," she said.
What melts first?
Antarctica is primarily divided into two sectors: West Antarctica, where the ice sheet sits in the ocean, and East Antarctica, where the ice sheet primarily sits on land. During the warm periods of the Pliocene, large parts of West Antarctica and some low-lying areas of East Antarctica experienced significant ice-melt, contributing to a 3- to 10-foot rise in global sea levels.
One of the study's main conclusions: Under warming conditions similar to the Pliocene, the part of West Antarctica located adjacent to the Pacific Ocean will see its ice disappear at a faster rate. Over the long term, however, both oceanic and atmospheric warming will contribute to rising global sea levels.
You can think of it as an equation of sorts: A warmer climate leads to less sea ice around Antarctica, which then causes the ocean to heat up. Due to the warmer water, the parts of the ice sheet sitting on the ocean melt first. Over time, as the climate continues to warm, the ice sitting on land will also retreat.
"In other words, it's a one-two punch on the system with a consequence of raising sea levels globally," Patterson said.
What you may not realize: Because of gravitational effects similar to ocean tides, the loss of ice in the Southern Hemisphere actually has a greater impact on coastlines in the Northern Hemisphere. Conversely, when ice sheets lose mass in the Northern Hemisphere, Southern Hemisphere coastlines are affected more.
With that in mind, New York would be more affected by a 7-meter rise in sea levels from the loss of Antarctic ice than a similar rise from melting ice sheets in Greenland, Patterson pointed out.
Geological archives and modeling experiments provide the long-term context needed to evaluate current changes and help scientists identify the mechanisms that drive the climate system. Ultimately, this research may help us formulate more accurate predictions about our climate change future.
"Basically, geological archives serve as a vital tool for testing the accuracy of climate models used to project future scenarios," Patterson said.
