From left, Assistant Professor Michael Diamond and graduate student alumnus Anthony Freveletti. Photo Credits: Diamond photo by Devin Bittner/FSU College of Arts. Freveletti by Sydney Tapscott
Scientific Frontline: Extended "At a Glance" Summary: Ocean Temperature Drivers
The Core Concept: Long-term sea-surface temperature changes in the Atlantic Ocean are primarily driven by human emissions, whereas temperature shifts in the Pacific Ocean are largely governed by natural, internal ocean variability.
Key Distinction/Mechanism: Contrary to older models that attributed Atlantic temperature shifts to natural currents like the Atlantic Meridional Overturning Circulation (AMOC), advanced statistical analysis separates slow-evolving anthropogenic changes from fast-evolving natural fluctuations. This reveals that Atlantic variations are essentially a complex interplay of greenhouse gas warming and aerosol cooling.
Major Frameworks/Components:
- Rotated Low-Frequency Component Analysis (RLFCA): A statistical methodology adapted to extract, identify, and reorganize patterns of temperature change based on their evolutionary speed and known external influences.
- Anthropogenic Forcing: The accumulation of human-produced greenhouse gas emissions and air pollution (aerosols) that collectively act as the primary driver of historical and future Atlantic temperatures.
- Pacific Decadal Oscillation: A long-term natural climate pattern in the Pacific Ocean that fluctuates every 20 to 30 years, serving as the primary unforced driver for regional sea-surface temperatures.
Branch of Science: Meteorology, Climatology, and Oceanography.
Future Application: The predictive frameworks developed in this research will help inform long-term infrastructure planning, guide risk-reduction measures for vulnerable Atlantic coastal communities, and refine the accuracy of future global climate models.
Why It Matters: Establishing that Atlantic temperature trends are largely human-driven rather than cyclical indicates that past phenomena, such as the spike in hurricane frequency since 1990, are not purely natural; consequently, future human emission trajectories will be the decisive factor in Atlantic weather patterns.
Florida State University researchers have identified key differences in the root causes of long-term sea-surface temperature changes across the Atlantic and Pacific Oceans, a finding that could help guide future research on ocean variability.
Research by assistant professor of meteorology Michael Diamond and FSU meteorology graduate alumnus Anthony Freveletti found that long-term temperature changes in the Pacific Ocean are driven primarily by internal ocean variability, while those in the Atlantic are largely the result of human emissions.
The study, conducted with assistant professor Robert Jnglin Wills from the ETH Zürich Institute for Atmospheric and Climate Science, was published this spring in Geophysical Research Letters.
“We know that important sources of natural variability in Earth’s climate system exist, and our ability to distinguish between these natural and human-forced sources of temperature variability is key to projecting future temperatures and their related impacts on society,” Diamond said.
Historical temperature swings in the Atlantic Ocean have long been considered one of those natural sources of variability in Earth’s climate.
Long-term shifts between increasing and decreasing Atlantic sea-surface temperatures were typically thought to be driven by the Atlantic Meridional Overturning Circulation, or AMOC, a system of currents in the Atlantic Ocean that is part of the network of natural ocean currents moving water around the world.
“Our findings contradict this theory, as we found that long-term changes in the Atlantic are more directly related to anthropogenic—human-produced—causes such as greenhouse gases and aerosols,” Freveletti said.
While most variability in global oceanic sea-surface temperatures was often thought to be driven by natural causes, the team’s findings suggest that only the oscillations in the Pacific are primarily driven by natural climate processes.
Most people, for example, are familiar with El Niño and La Niña, two opposing climate patterns in the tropical Pacific that occur every 2 to 7 years on average. The Pacific Decadal Oscillation, which Freveletti and Diamond studied, is a similar climate pattern that fluctuates over much longer periods, typically every 20 to 30 years.
Using the programming language Python for data analysis, the team applied a new statistical method called rotated low-frequency component analysis, or RLFCA, to climate model datasets from 1920 through 2025. RLFCA is an adaptation of a low-frequency component analysis method previously developed by Wills that identifies and extracts patterns of temperature change based on how quickly they evolve over time.
“Since human emissions build up in the atmosphere over many years, the temperature changes they cause develop gradually over time,” Freveletti said. “In contrast, natural fluctuations driven by factors such as ocean currents, wind patterns, and air pressure occur more rapidly. Our analysis effectively separates these forced and unforced changes within those data trends by identifying which patterns are fast-evolving and which are slow-evolving.”
Freveletti expanded upon this method by adding a “rotational” step that reorganizes identified patterns with known external influences, calculated by climate models, helping to distinguish the causes of temperature variability.
The team found that what looked like natural variability in the Atlantic Ocean was actually an overlap between air pollution and aerosols shading and cooling the sea surface, and greenhouse gas emissions warming the entire globe.
“Our results show that a complex interplay of air pollution and greenhouse gas emissions is responsible for historical temperature patterns in the Atlantic Ocean that led to various weather phenomena, such as a spike in hurricane frequency since 1990,” Diamond said. “We should not expect to return to an inactive hurricane era by chance alone; the future of human emissions will be the most important driver of Atlantic temperatures going forward.”
While natural climate patterns like El Niño and La Niña can affect weather, ecosystems, and economies through variability in rainfall, temperature, and storm activity, their effects are temporary. Greenhouse gas emissions, by contrast, accumulate over time and have longer-lasting impacts. The researchers said their findings could help inform infrastructure planning along the Atlantic coast, including measures to reduce risks to coastal communities.
Reference material:
Published in journal: Geophysical Research Letters
Authors: Anthony S. Freveletti, Michael S. Diamond, and Robert C. J. Wills
Source/Credit: Florida State University | Jack Labruno
Edited by: Scientific Frontline
Reference Number: as061726_01