̽��ֱ�� of Cambridge - Scott Polar Research Institute

Planting trees in the Arctic could make global warming worse, not better, say scientists

sc604 — Thu, 07 Nov 2024 13:41:21 +0000

But, writing in the journal Nature Geoscience, an international group of scientists, led by the ̽��ֱ�� of Cambridge and the ̽��ֱ�� of Århus, argue that tree planting at high latitudes will accelerate, rather than decelerate, global warming.

As the climate continues to warm, trees can be planted further and further north, and large-scale tree-planting projects in the Arctic have been championed by governments and corporations as a way to mitigate the worst effects of climate change.

However, when trees are planted in the wrong places - such as normally treeless tundra and mires, as well as large areas of the boreal forest with relatively open tree canopies - they can make global warming worse.

According to lead author Assistant Professor Jeppe Kristensen from Aarhus ̽��ֱ�� in Denmark, the unique characteristics of Arctic and sub-Arctic ecosystems make them poorly suited for tree planting for climate mitigation.

“Soils in the Arctic store more carbon than all vegetation on Earth,” said Kristensen. “These soils are vulnerable to disturbances, such as cultivation for forestry or agriculture, but also the penetration of tree roots. ̽��ֱ��semi-continuous daylight during the spring and early summer, when snow is still on the ground, also makes the energy balance in this region extremely sensitive to surface darkening, since green and brown trees will soak up more heat from the sun than white snow.”

In addition, the regions surrounding the North Pole in North America, Asia and Scandinavia are prone to natural disturbances - such as wildfires and droughts - that kill off vegetation. Climate change makes these disturbances both more frequent and more severe.

“This is a risky place to be a tree, particularly as part of a homogeneous plantation that is more vulnerable to such disturbances,” said Kristensen. “ ̽��ֱ��carbon stored in these trees risks fuelling disturbances and getting released back to the atmosphere within a few decades.”

̽��ֱ��researchers say that tree planting at high latitudes is a prime example of a climate solution with a desired effect in one context but the opposite effect in another.

“ ̽��ֱ��climate debate is very carbon-focused because the main way humans have modified the Earth’s climate in the last century is through emitting greenhouse gases from burning fossil fuels,” said Kristensen. “But at the core, climate change is the result of how much solar energy entering the atmosphere stays, and how much leaves again – Earth’s so-called energy balance.”

Greenhouse gases are one important determinant of how much heat can escape our planet’s atmosphere. However, the researchers say that at high latitudes, how much sunlight is reflected back into space, without being converted into heat (known as the albedo effect), is more important than carbon storage for the total energy balance.

̽��ֱ��researchers are calling for a more holistic view of ecosystems to identify truly meaningful nature-based solutions that do not compromise the overall goal: slowing down climate change.

“A holistic approach is not just a richer way of looking at the climate effects of nature-based solutions, but it’s imperative if we’re going to make a difference in the real world,” said senior author Professor Marc Macias-Fauria, from the ̽��ֱ�� of Cambridge’s Scott Polar Research Institute.

However, the researchers recognise that there can be other reasons for planting trees, such as timber self-sufficiency, but these cases do not come with bonuses for climate mitigation.

“Forestry in the far North should be viewed like any other production system and compensate for its negative impact on the climate and biodiversity,” said Macias-Fauria. “You can’t have your cake and eat it, and you can’t deceive the Earth. By selling northern afforestation as a climate solution, we’re only fooling ourselves.”

So how can we moderate global warming at high latitudes? ̽��ֱ��researchers suggest that working with local communities to support sustainable populations of large herbivores, such as caribou, could be a more viable nature-based solution to climate change in Arctic and subarctic regions than planting millions of trees.

“There is ample evidence that large herbivores affect plant communities and snow conditions in ways that result in net cooling,” said Macias-Fauria. “This happens both directly, by keeping tundra landscapes open, and indirectly, through the effects of herbivore winter foraging, where they modify the snow and decrease its insulation capacity, reducing soil temperatures and permafrost thaw.”

̽��ֱ��researchers say it’s vital to consider biodiversity and the livelihoods of local communities in the pursuit of nature-based climate solutions.

“Large herbivores can reduce climate-driven biodiversity loss in Arctic ecosystems and remain a fundamental food resource for local communities,” said Macias-Fauria. “Biodiversity and local communities are not an added benefit to nature-based solutions: they are fundamental. Any nature-based solutions must be led by the communities who live at the front line of climate change.”

More about this story

Reference:
Jeppe Å Kristensen et al. ‘Tree planting is no climate solution at northern high latitudes.’ Nature Geoscience (2024). DOI: 10.1038/s41561-024-01573-4

Explore more discoveries, innovations and research on climate and nature at the ̽��ֱ�� of Cambridge: www.cam.ac.uk/climate-and-nature

Tree planting has been widely touted as a cost-effective way of reducing global warming, due to trees’ ability to store large quantities of carbon from the atmosphere.

Pierre Longnus via Getty Images

Emerald Lake, Yukon

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Antarctic ice shelves hold twice as much meltwater as previously thought

sc604 — Thu, 27 Jun 2024 08:56:09 +0000

Slush – water-soaked snow – makes up more than half of all meltwater on the Antarctic ice shelves during the height of summer, yet is poorly accounted for in regional climate models.

Cambridge on World Environment Day 2024

plc32 — Wed, 05 Jun 2024 06:01:21 +0000

This year's World Environment Day focus is on land restoration. So we spoke with three Cambridge researchers working on reviving landscapes, boosting biodiversity, and collaborating with communities to mitigate and adapt to the impacts of climate change.

Ice shelves fracture under weight of meltwater lakes

sc604 — Fri, 03 May 2024 14:31:26 +0000

When air temperatures in Antarctica rise and glacier ice melts, water can pool on the surface of floating ice shelves, weighing them down and causing the ice to bend. Now, for the first time in the field, researchers have shown that ice shelves don’t just buckle under the weight of meltwater lakes — they fracture.

As the climate warms and melt rates in Antarctica increase, this fracturing could cause vulnerable ice shelves to collapse, allowing inland glacier ice to spill into the ocean and contribute to sea level rise.

Ice shelves are important for the Antarctic Ice Sheet’s overall health as they act to buttress or hold back the glacier ice on land. Scientists have predicted and modelled that surface meltwater loading could cause ice shelves to fracture, but no one had observed the process in the field, until now.

̽��ֱ��new study, published in the Journal of Glaciology, may help explain how the Larsen B Ice Shelf abruptly collapsed in 2002. In the months before its catastrophic breakup, thousands of meltwater lakes littered the ice shelf’s surface, which then drained over just a few weeks.

To investigate the impacts of surface meltwater on ice shelf stability, a research team led by the ̽��ֱ�� of Colorado Boulder, and including researchers from the ̽��ֱ�� of Cambridge, travelled to the George VI Ice Shelf on the Antarctic Peninsula in November 2019.

First, the team identified a depression or ‘doline’ in the ice surface that had formed by a previous lake drainage event where they thought meltwater was likely to pool again on the ice. Then, they ventured out on snowmobiles, pulling all their science equipment and safety gear behind on sleds.

Around the doline, the team installed high-precision GPS stations to measure small changes in elevation at the ice’s surface, water-pressure sensors to measure lake depth, and a timelapse camera system to capture images of the ice surface and meltwater lakes every 30 minutes.

In 2020, the COVID-19 pandemic brought their fieldwork to a screeching halt. When the team finally made it back to their field site in November 2021, only two GPS sensors and one timelapse camera remained; two other GPS and all water pressure sensors had been flooded and buried in solid ice. Fortunately, the surviving instruments captured the vertical and horizontal movement of the ice’s surface and images of the meltwater lake that formed and drained during the record-high 2019/2020 melt season.

GPS data indicated that the ice in the centre of the lake basin flexed downward about a foot in response to the increased weight from meltwater. That finding builds upon previous work that produced the first direct field measurements of ice shelf buckling caused by meltwater ponding and drainage.

̽��ֱ��team also found that the horizontal distance between the edge and centre of the meltwater lake basin increased by over a foot. This was most likely due to the formation and/or widening of circular fractures around the meltwater lake, which the timelapse imagery captured. Their results provide the first field-based evidence of ice shelf fracturing in response to a surface meltwater lake weighing down the ice.

“This is an exciting discovery,” said lead author Alison Banwell, from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the ̽��ֱ�� of Colorado Boulder. “We believe these types of circular fractures were key in the chain reaction style lake drainage process that helped to break up the Larsen B Ice Shelf.”

“While these measurements were made over a small area, they demonstrate that bending and breaking of floating ice due to surface water may be more widespread than previously thought,” said co-author Dr Rebecca Dell from Cambridge’s Scott Polar Research Institute. “As melting increases in response to predicted warming, ice shelves may become more prone to break up and collapse than they are currently.”

“This has implications for sea level as the buttressing of inland ice is reduced or removed, allowing the glaciers and ice streams to flow more rapidly into the ocean,” said co-author Professor Ian Willis, also from SPRI.

̽��ֱ��work supports modelling results that show the immense weight of thousands of meltwater lakes and subsequent draining caused the Larsen B Ice Shelf to bend and break, contributing to its collapse.

“These observations are important because they can be used to improve models to better predict which Antarctic ice shelves are more vulnerable and most susceptible to collapse in the future,” Banwell said.

̽��ֱ��research was funded by the U.S. National Science Foundation (NSF) and the Natural Environment Research Council (NERC), part of UK Research and Innovation (UKRI). ̽��ֱ��team also included researchers from the ̽��ֱ�� of Oxford and the ̽��ֱ�� of Chicago. Rebecca Dell is a Fellow of Trinity Hall, Cambridge.

Reference:
Alison F Banwell et al. ‘Observed meltwater-induced flexure and fracture at a doline on George VI Ice Shelf, Antarctica.’ Journal of Glaciology (2024). DOI: 10.1017/jog.2024.31

Adapted from a CIRES press release.

Heavy pooling meltwater can fracture ice, potentially leading to ice shelf collapse

Ian Willis

Ali Banwell and Laura Stevens installing the time-lapse camera used in this study on the George VI Ice Shelf in Antarctica.

Yes

Ice sheets can collapse faster than previously thought possible

sc604 — Wed, 05 Apr 2023 14:59:35 +0000

An international team of researchers used high-resolution imagery of the seafloor to reveal just how quickly a former ice sheet that extended from Norway retreated at the end of the last Ice Age, about 20,000 years ago.

̽��ֱ��team, including researchers from the ̽��ֱ�� of Cambridge, mapped more than 7,600 small-scale landforms called corrugation ridges across the seafloor. ̽��ֱ��ridges are less than 2.5 metres high and are spaced between about 25 and 300 metres apart.

These landforms are understood to have formed when the ice sheet’s retreating margin moved up and down with the tides, pushing seafloor sediments into a ridge every low tide. Given that two ridges would have been produced each day, the researchers were able to calculate how quickly the ice sheet retreated.

Their results, reported in the journal Nature, show the former ice sheet underwent pulses of rapid retreat at a speed of 50 to 600 metres per day. This is much faster than any ice sheet retreat rate that has been observed from satellites or inferred from similar landforms in Antarctica.

“Our research provides a warning from the past about the speeds that ice sheets are physically capable of retreating at,” said Dr Christine Batchelor from Newcastle ̽��ֱ��, who led the research. “Our results show that pulses of rapid retreat can be far quicker than anything we’ve seen so far.”

Information about how ice sheets behaved during past periods of climate warming is important to inform computer simulations that predict future ice sheet and sea-level change.

“This study shows the value of acquiring high-resolution imagery about the glaciated landscapes that are preserved on the seafloor,” said co-author Dr Dag Ottesen from the Geological Survey of Norway, who is involved in the MAREANO seafloor mapping programme that collected the data.

̽��ֱ��new research suggests that periods of such rapid ice-sheet retreat may only last for short periods of time: from days to months.

“This shows how rates of ice-sheet retreat averaged over several years or longer can conceal shorter episodes of more rapid retreat,” said co-author Professor Julian Dowdeswell from Cambridge’s Scott Polar Research Institute. “It is important that computer simulations are able to reproduce this ‘pulsed’ ice-sheet behaviour.”

̽��ֱ��seafloor landforms also shed light into the mechanism by which such rapid retreat can occur. ̽��ֱ��researchers found that the former ice sheet had retreated fastest across the flattest parts of its bed.

“An ice margin can unground from the seafloor and retreat near-instantly when it becomes buoyant,” said co-author Dr Frazer Christie, also from the Scott Polar Research Institute. “This style of retreat only occurs across relatively flat beds, where less melting is required to thin the overlying ice to the point where it starts to float.”

̽��ֱ��researchers conclude that pulses of similarly rapid retreat could soon be observed in parts of Antarctica. This includes at West Antarctica’s vast Thwaites Glacier, which is the subject of considerable international research due to its potential susceptibility to unstable retreat. ̽��ֱ��authors of this new study suggest that Thwaites Glacier could undergo a pulse of rapid retreat because it has recently retreated close to a flat area of its bed.

“Our findings suggest that present-day rates of melting are sufficient to cause short pulses of rapid retreat across flat-bedded areas of the Antarctic Ice Sheet, including at Thwaites”, said Batchelor. “Satellites may well detect this style of ice-sheet retreat in the near future, especially if we continue our current trend of climate warming.”

Other co-authors are Dr Aleksandr Montelli and Evelyn Dowdeswell at the Scott Polar Research Institute, Dr Jeffrey Evans at Loughborough ̽��ֱ��, and Dr Lilja Bjarnadóttir at the Geological Survey of Norway. ̽��ֱ��study was supported by Peterhouse, Cambridge, the Faculty of Humanities and Social Sciences at Newcastle ̽��ֱ��, the Prince Albert II of Monaco Foundation, and the Geological Survey of Norway.

Reference:
Christine L Batchelor et al. ‘Rapid, buoyancy-driven ice-sheet retreat of hundreds of metres per day’. Nature (2023), DOI: 10.1038/s41586-023-05876-1

Adapted from a press release by Newcastle ̽��ֱ��.

Ice sheets can retreat up to 600 metres a day during periods of climate warming, 20 times faster than the highest rate of retreat previously measured.

Copernicus EU/ESA, processed by Dr Frazer Christie

Sentinel-1 image composite depicting the highly fractured and fast-flowing frontal margin of the Thwaites and Crosson ice shelves

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Researchers build more detailed picture of the movement of Greenland Ice Sheet

sc604 — Fri, 10 Feb 2023 15:14:39 +0000

Researchers have found that the movement of glaciers in Greenland is more complex than previously thought, with deformation in regions of warmer ice containing small amounts of water accounting for motion that had often been assumed to be caused by sliding where the ice meets the bedrock beneath.

Runaway West Antarctic ice retreat can be slowed by climate-driven changes in ocean temperature

sc604 — Mon, 16 Jan 2023 09:45:30 +0000

New research finds that ice-sheet-wide collapse in West Antarctica isn’t inevitable: the pace of ice loss varies according to regional differences in atmosphere and ocean circulation.

Seasonal change in Antarctic ice sheet movement observed for first time

sc604 — Thu, 06 Oct 2022 11:40:23 +0000

Some estimates of Antarctica’s total contribution to sea-level rise may be over- or underestimated, after researchers detected a previously unknown source of ice loss variability.