Unique Siberian tundra is on the way to complete disappearance from the face of the planet

(ORDO NEWS) — The Siberian tundra could be gone by the year 2500 if greenhouse gas emissions are not drastically reduced.

Even in the best-case scenario, two-thirds of this landscape – defined by a short growing season and a cover of grasses, mosses, shrubs and lichens – could disappear, leaving behind two fragments separated by 1,553 miles (2,500 km), scientists recently predicted.

And as the permafrost melts, the tundra could release massive amounts of accumulated greenhouse gases into the atmosphere, potentially accelerating global warming.

“We were stunned to see how quickly the tundra turns into a forest,” said ecologist and forest modeller Stefan Kruse from the Alfred Wegener Institute (AWI) Helmholtz Center for Polar and Marine Research in Bremerhaven, Germany.

The loss of the tundra would not only be a blow to biodiversity and human culture, but could exacerbate warming in the Arctic.

In recent decades, the Arctic has been warming at a rapid pace, about twice as fast as the rest of the globe. From 1960 to 2019, temperatures in the Arctic region rose nearly 7.2 degrees Fahrenheit (4 degrees Celsius), according to the National Snow and Ice Data Center (NSIDC).

This heat has reduced the extent of sea ice and is also affecting the Arctic land masses. One of these consequences is the northward expansion of Siberian larch forests.

How quickly these forests will replace the grassy, ​​shrubby tundra ecosystem is unknown. Tree line changes with climate are not the same around the world, Kruse said.

In some areas, forest stands have moved north. In others they remain motionless, and in still others they even recede. Previous studies in the Siberian tundra have focused on small areas, but there can be many variations from site to site.

Now Kruse and his colleague, AWI professor Ulrike Hertzschuch, have created a new computer model that estimates the entire 2,485-mile (4,000 km) expanse of the Siberian tundra.

The model takes into account the life cycles of individual trees, from how far they can spread their seeds, to how well they grow when faced with competition from other trees, to growth rates depending on temperature, rainfall, and the depth of summer permafrost thaw. which occurs in the tundra regions.

The researchers found that once trees begin moving north in response to warming temperatures, they do so quickly – and are unlikely to retreat again if temperatures cool.

Under a scenario where carbon emissions are zero by 2100 and global temperature rise does not exceed 3.6 degrees Celsius (2 degrees C), only 32.7 percent of today’s tundra will remain by 2500.

This part will be divided into two mini-tundras: one in Chukotka in the far east and one in the Taimyr Peninsula in the far north.

Cascade of changes

But even this bleak scenario may not be feasible without very quick action, which means the outcome for the tundra could be far worse.

In an intermediate scenario in which carbon emissions start to decline only in 2050 and halve by 2100, by 2500 larch trees will cover all but 5.7% of the current tundra, destroying the ecosystem.

In warmer global scenarios, trees could spread as much as 18.6 miles (30 km) north, the researchers reported May 24 in the journal eLife.

When Kruse and Hertzschuch tested what would happen if temperatures cooled after the tundra turned into forest, they found that the tree line was not receding as fast as it was advancing. Once mature trees have matured, they can handle a lot, Kruse says.

The study did not directly model what might happen to tundra dwellers such as reindeer, Kruse said, but dividing populations into two regions where they are cut off from interbreeding is usually bad for species survival.

Reindeer (known as caribou in North America) migrate from north to south and back again throughout the year, and it is not known how forest expansion may affect their migration and life cycles.

The impact is likely to be felt by people as well. Indigenous peoples such as the Nenets living in northwestern Siberia practice reindeer herding and hunting.

“The culture partly depends on the tundra,” says Kruse. “If it disappears, it will be a great loss for humanity.”

How the loss of the tundra could affect future warming is also unknown, but covering mossy, spiny meadows with tall trees could make things worse. The snow-covered tundra is lighter in color than the canopy of the larch forest; therefore forests will absorb more heat than tundra, potentially making the Arctic hotter and faster, Kruse said.

This additional heat could accelerate and deepen the melting of permafrost in the tundra, which accumulates huge amounts of greenhouse gases – up to 1,400 gigatons globally, according to NSIDC. Melting permafrost can release these gases, as well as long-frozen microbes and viruses.

Changes are likely to go beyond replacing the tundra with larches, Kruse added. As warmer summers thaw ever deeper layers of permafrost, evergreen trees may also move there.

These trees remain leafy all year round, potentially absorbing even more heat than larches. The southern part of the taiga, where temperatures are already warmer than in the north, is likely to warm even more, leading to drought and forest fires that release even more carbon into the atmosphere.

The findings provide compelling reasons to pursue ambitious reductions in fossil fuel emissions.

However, the model used in the study can also be used to determine the most resilient areas of the Siberian tundra, Kruse said. These sustainable areas can be prioritized for conservation investments.

“The best option would be to cut global greenhouse gas emissions to relieve the pressure,” he said. “But still, if we can’t do that, we need to do conservation.”

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