Using nearly a decade of satellite data, researchers show how glaciers worldwide speed up and slow down with the changing of the seasons – annual rhythms that reveal how Earth’s ice may respond to long-term climate warming. The findings show that glaciers in regions that reach above-freezing temperatures experience the largest seasonal swings in ice flow, and rising temperatures may amplify these movements and shift their timing worldwide. Earth’s glaciers and ice sheets have been rapidly shrinking in recent decades, and their future contribution to sea-level rise and other glacial hazards depends on the rate at which they continue to react to ongoing climate warming. However, the physical processes that govern the movement of ice are complex and incompletely understood. Investigating how glaciers respond to short-term seasonal variation in temperature and environmental conditions offers a natural laboratory for studying the ice flow dynamics. It’s well observed that glaciers worldwide show substantial seasonal swings in velocity driven by several factors. Yet despite these insights, a comprehensive quantitative understanding of the full range of seasonal glacier dynamics across regions and glacier types remains lacking.

To understand the full scope of seasonal glacier dynamics and the mechanisms that drive them, Chad Greene and Alex Gardner conducted a comprehensive global assessment of how glaciers speed up and slow down over the course of a year. Using nearly a decade of NASA satellite data – drawn from more than 36 million pairs of high-resolution images collected between 2014 and 2022 – Greene and Gardner analyzed the seasonal movement of every land glacier larger than 5 square kilometers on Earth. The approach allowed the authors to quantify how often and how strongly glaciers accelerate and decelerate throughout the year and map where ice is most sensitive to seasonal environmental forcing. According to the findings, seasonal variations in ice velocity are strongly controlled by local air temperatures. In temperate regions where annual maximum temperatures exceed 0 degrees Celsius, glaciers reach peak flow earlier in the year.  The authors suggest that this occurs because surface meltwater rapidly increases water pressure beneath the glacier, reducing friction and accelerating ice movement. Moreover, the study finds that, globally, glaciers with strong seasonal variability also tended to show a weak but measurable correlation with larger year-to-year variability in flow. While this does not mean that seasonal shifts result in long-term change, it does suggest that both are influenced by glacier shape and subglacial conditions. In a Perspective, Lizz Ultee discusses the study in greater detail.

For reporters interested in topics of research integrity, author Chad Green notes, “Our results are the outcome of open data sharing and NASA policies that make satellite data public and freely available to all. Open science and the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) program that funded this work maximize scientific integrity by making the scientific process fully transparent and replicable. We’re proud that anyone with a computer can download data collected by NASA for free and access our code to confirm our results.”