Thick ice deposits along Arctic rivers are melting significantly faster than they did earlier this century.

A new study has pinpointed climate change as the most likely factor for ice deposits to disappear nearly a month earlier than they did in 2000.

River icings form from groundwater that reaches the surface and solidifies on top of frozen rivers. They grow throughout the winter until river valleys are choked with ice and some river icings have grown to more than 10 square kilometers in area and can be more than 10 meters thick.

In the past the icings have melted out around mid-July but a new study measuring the extent of river icings in the U.S. and Canadian Arctic shows most river icings disappeared 26 days earlier in 2015 than they did in 2000, melting in mid-June on average.

“This is the first clear evidence that this important component of Arctic river systems—which we didn’t know was changing—is changing and it’s changing rapidly,” Tamlin Pavelsky, a hydrologist at the University of North Carolina and lead author of the new study, said in a statement.

Until this recent study, scientists have not examined whether river icings are changing in response to a warming climate and while the decline in river icings is likely a result of climate change, according to the authors, they are unsure whether the decline in river icings is a direct result of rising temperatures or if climate change is altering how rivers and groundwater interact.

“While glaciers tell us about climate in the mountains and sea ice tells us about sea-atmosphere interactions, the processes that control river icing may offer great insight into how groundwater and surface waters are connected in the Arctic and how our headwaters will be connected to the ocean in the future,” Jay Zarnetske, a hydrologist at Michigan State University in East Lansing, Michigan, and co-author of the study, said in a statement.

According to Pavelsky, the decline in river icings is rapid and if it continues it could have a significant impact on the Arctic river ecosystems.

River icings, which are found throughout the Arctic, create wide channels that are habitats for animals and fish. Water is tied up in river icings so that when they melt in summer, usually in July and August, they keep rivers flowing that might otherwise dry up, providing freshwater habitats for fish and other animals.

The researchers detected 147 river icings using the moderate-resolution imaging spectroradiometer aboard the NASA Terra satellite and discovered that 84 of the river icings are either becoming smaller or disappearing earlier in the season. Also, none of the river icings analyzed grew or persisted later in the season.

The minimum area of ice they measured also shrank considerably over the course of the study. In 2000 the researchers measured the minimum ice area to be 80 square kilometers, while by 2010 the number decreased to just four square kilometers. By 2015 the area increased to about seven square kilometers.

The study was published in Geophysical Research Letters.