by As the Arctic warms, its major rivers are changing in ways that could have huge consequences – not just for the Arctic region but for the world.
Rivers are the terrestrial branch of the world’s hydrological cycle. As rain and snow fall, rivers carry freshwater runoff as well as dissolved organic and particulate matter, including carbon, to coastal areas. With the Arctic now warming almost four times faster than the rest of the world, the region is seeing more precipitation and melting permafrost, leading to stronger river flows.
We are climate scientists who study the impact of warming on the water cycle and ecosystems. In a new study using historical data and sophisticated computer models of Earth’s climate and hydrology, we explored how climate change is changing Arctic rivers.
We found that permafrost and intense storms will change the way water moves into and through Arctic rivers. These changes will affect coastal regions, the Arctic Ocean and possibly the North Atlantic, as well as the climate.
Melting permafrost: Major changes in Arctic soils
Permafrost melting is one of the most consequential changes occurring in the Arctic as temperatures rise.
Permafrost is soil that has been frozen for at least two years and often for thousands of years. It covers about 8.8 million square miles (about 22.8 million square kilometers) in the Earth’s Northern Hemisphere, but that area is shrinking as the permafrost melts.
Historically, most of the water that enters Arctic rivers flows on top of frozen permafrost soils in the spring. Scientists call this “overland runoff”.
However, our results suggest that as warming continues, an increasing fraction of annual river flow will come from the surface, via thawed soils in the degraded permafrost. As the overall flow increases with more precipitation, up to 30% more of it could be moving underground by the end of this century as subsurface pathways increase.
When water flows through the soil, it picks up various chemicals and metals. As a result, water entering rivers is likely to have a different chemical character. For example, it may carry more nutrients and dissolved carbon that could affect coastal zones and the global climate. The fate of that sequestered carbon is an active area of study.
River water may contain more carbon “out of range” when it reaches clear coastal waters, increasing the amount of carbon dioxide released into the atmosphere, further fueling climate warming. The thaw is also revealing other nasty surprises, like the emergence of long-frozen viruses.
More rain and snow, more runoff
The Arctic water cycle is also increasing as temperatures rise, which means more precipitation, evaporation, plant transpiration and river discharge. This is mainly due to the inherent ability of a warmer atmosphere to hold more moisture. It is the same reason that more blizzards are occurring as the climate warms.
Our study found that most of the additional precipitation will occur across the far northern parts of the Arctic basin. As sea ice disappears in a warming climate, computer models agree that a more open Arctic Ocean will add more water to the atmosphere, where it will be transported to nearby land areas to fall as precipitation.
Snowfall in northern Alaska, Siberia and Canada will result in more water flowing into rivers, possibly up to 25% more under a high warming scenario based on our research. There is more carbon in the soil in northern parts of the Arctic compared to the south. As permafrost melts, those regions will also see more water entering rivers from the surface, where additional soil carbon can leach into the water and become dissolved organic carbon.
More ancient carbon is already showing up in samples collected from Arctic rivers, attributed to melting permafrost. Carbon dating shows that some of this carbon has been frozen for thousands of years.
Impacts will pass through Arctic ecosystems
So what does the future hold?
One of the most significant changes expected is the transport of fresh water and associated materials, such as dissolved organic carbon and heat energy, to Arctic coastal zones.
Coastal lagoons may become fresher. This change would affect organisms up and down the food chain, although our current understanding of the potential impacts of changes in fresh water and dissolved organic carbon remains unclear.
River water will also be warmer as the climate warms and may melt coastal sea ice earlier in the season. Scientists noticed this in the spring of 2023, when unusually warm water in Canada’s Mackenzie River transported heat to the Beaufort Sea, contributing to the early melting of coastal sea ice.
Finally, more river water reaching the coast has the potential to refresh the Arctic Ocean, especially along northern Eurasia, where Russia’s major rivers export huge amounts of fresh water each year.
There is concern that increased river flows in that region are affecting the Atlantic Longitudinal Gyre, the currents that spread heat from the tropics, up the US East Coast and towards Europe. Evidence is mounting that these currents have been slowing down in recent years as more fresh water enters the North Atlantic. If the circulation stops, it would greatly affect temperatures across North America and Europe.
Along the coast, changing river flows will also affect the plants, animals and Indigenous populations that call the region home. For them and for the global climate, the results of our study highlight the need to closely monitor how the Arctic is changing and to take steps to mitigate the effects.
This article is republished from The Conversation, a non-profit, independent news organization that brings you reliable facts and analysis to help you make sense of our complex world. Written by: Michael A. Rawlins, UMass Amherst and Ambarish Karmalkar, University of Rhode Island
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Michael A. Rawlins receives funding from the Department of Energy, the National Aeronautics and Space Administration and the US National Science Foundation.
Ambarish Karmalkar receives funding from the Department of Energy and the United States Geological Survey.
