̽��ֱ�� of Cambridge - global warming

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.

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.

̽��ֱ��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.

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Seeking climate justice at the 'world court'

fpjl2 — Wed, 29 Mar 2023 07:59:32 +0000

How a Cambridge professor helped the climate-embattled nation of Vanuatu put the question of global warming to the International Court of Justice for the first time in history.

Antarctic Ice Sheet study reveals 8,000-year record of climate change

sjr81 — Mon, 12 Dec 2016 16:02:17 +0000

Results of the study, co-authored by Michael Weber, a paleoclimatologist and visiting scientist at the ̽��ֱ�� of Cambridge, along with colleagues from the USA, New Zealand and Germany, are published this week in the journal Nature.

Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a climate modeller from the MARUM Center for Marine Environmental Studies at the ̽��ֱ�� of Bremen in Germany.

̽��ֱ��researchers first turned their attention to the Scotia Sea. “Most icebergs calving off the Antarctic Ice Sheet travel through this region because of the atmospheric and oceanic circulation,” explained Weber. “ ̽��ֱ��icebergs contain gravel that drop into the sediment on the ocean floor – and analysis and dating of such deposits shows that for the last 8,000 years, there were centuries with more gravel and those with less.”

̽��ֱ��research team’s hypothesis is that climate modellers have historically overlooked one crucial element in the overall climate system. They discovered that the centuries-long phases of enhanced and reduced Antarctic ice mass loss documented over the past 8,000 years have had a cascading effect on the entire climate system.

Using sophisticated computer modelling, the researchers traced the variability in iceberg calving (ice that breaks away from glaciers) to small changes in ocean temperatures.

“There is a natural variability in the deeper part of the ocean adjacent to the Antarctic Ice Sheet that causes small but significant changes in temperatures,” said co-author Andreas Schmittner, a climate modeller from Oregon State ̽��ֱ��. “When the ocean temperatures warm, it causes more direct melting of the ice sheet below the surface, and it increases the number of icebergs that calve off the ice sheet.”

Those two factors combine to provide an influx of fresh water into the Southern Ocean during these warm regimes, according to Peter Clark, a paleoclimatologist from Oregon State ̽��ֱ��, and co-author on the study.

“ ̽��ֱ��introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water,” he said. “ ̽��ֱ��cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface.”

̽��ֱ��discovery may help explain why sea ice is currently expanding in the Southern Ocean despite global warming, the researchers say.

“This response is well-known, but what is less-known is that the input of fresh water also leads to changes far away in the northern hemisphere, because it disrupts part of the global ocean circulation,” explained Nick Golledge from the ̽��ֱ�� of Wellington, New Zealand, an ice-sheet modeller and study co-author. “Meltwater from the Antarctic won’t just raise global sea level, but might also amplify climate changes around the world. Some parts of the North Atlantic may end up with warmer temperatures as a consequence of part of Antarctica melting.”

Golledge used a computer model to simulate how the Antarctic Ice Sheet changed as it came out of the last ice age and into the present, warm period.

" ̽��ֱ��integration of data and models provides further evidence that the Antarctic Ice Sheet has experienced much greater natural variability in the past than previously anticipated,” added Weber. “We should therefore be concerned that it will possibly act very dynamically in the future, too, specifically when it comes to projecting future sea-level rise.”

Two years ago Weber led another study, also published in Nature, which found that the Antarctic Ice Sheet collapsed repeatedly and abruptly at the end of the Last Ice Age to 19,000 to 9,000 years ago.

An international team of researchers has found that the Antarctic Ice Sheet plays a major role in regional and global climate variability – a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.

̽��ֱ��Antarctic Ice Sheet has experienced much greater natural variability in the past than previously anticipated.

Michael Weber

Iceberg in the Weddell Sea

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Opinion: Blocking out the sun won’t fix climate change – but it could buy us time

Anonymous — Thu, 19 Nov 2015 10:55:13 +0000

̽��ֱ��Paris climate talks hope to set out how we can reduce the amount of carbon we’re pumping into the atmosphere. But emissions cuts alone may not be enough. Atmospheric CO₂ is the blanket that keeps our planet warm and any further emissions will mean more global warming. Observations in recent years show that warming is accelerating, that polar ice and glaciers are all melting, that sea level is rising … it all looks rather bleak.

Could we directly engineer the climate and refreeze the poles? ̽��ֱ��answer is probably yes, and it could be a cheap thing to achieve – maybe costing only a few billion dollars a year. But doing this – or even just talking about it – is controversial.

Some have suggested there is a good business case to be made. We could carefully engineer the climate for a few decades while we work out how to reduce our dependency on carbon, and by taking our time we can protect the global economy and avoid financial crises. I don’t believe this argument for a minute, but you can see it’s a tempting prospect.

Reflecting the sun

One option might be to reflect some of the sun’s energy back into space. This is known as Solar Radiation Management (SRM), and it is the most viable climate engineering technology explored so far.

For instance we could spray sea water up out of the oceans to seed clouds and create more “whiteness”, which we know is a good way to reflect the heat of the sun. Others have proposed schemes to put mirrors in space, carefully located at the point between the sun and the Earth where gravity forces balance. These mirrors could reflect, say, 2% of the sun’s rays harmlessly into space, but the price tag puts them out of reach.

Perhaps a more immediate prospect for cooling the planet is to spray tiny particles high up into the stratosphere, at around 20km altitude – this is twice as high as normal commercial planes fly. To maximise reflectivity these particles would need to be around 0.5 micrometres across, like the finest of dust.

We know from large volcanic eruptions that particles injected at high altitude cool the planet. ̽��ֱ��1991 eruption of Mount Pinatubo in the Philippines is the best recent example. It is estimated that more than 10m tonnes of sulphur dioxide were propelled into the high atmosphere and it quickly formed tiny droplets of sulphuric acid (yes, the same stuff found in acid rain) which reflected sunlight and caused global cooling. For about a year after Pinatubo the Earth cooled by around 0.4℃ and then temperatures reverted to normal.

I was involved recently in the SPICE project (Stratospheric Particle Injection for Climate Engineering) and we looked at the possibility of injecting all sorts of particles, including titanium dioxide, which is also used as the pigment in most paints and is the active ingredient in sun lotion.

̽��ֱ��experiment to validate models of tether dynamics was cancelled Hugh Hunt, CC BY-SA

̽��ֱ��technology to deliver these particles is crazy – we looked at pumping them in a slurry up to 20km into the air using a giant hose suspended by a huge helium balloon. A small-scale experiment was cancelled because even it proved too controversial, too hot. Imagine if we demonstrate that this technology can work. Politicians could then claim there was a technical “fix” for climate change so there would be no need to cut emissions after all.

But this isn’t a ‘quick fix’

There are so many problems with climate engineering. ̽��ֱ��main one is that we have only one planet to work with (we have no Planet B) and if we screw this one up then what do we do? Say “sorry” I guess. But we’re already screwing it up by burning more than 10 billion tonnes of fossil fuels a year. We have to stop this carbon madness immediately.

Engineering the climate by reflecting sunlight doesn’t prevent more CO₂ being pumped into the atmosphere, some of which dissolves in the oceans causing acidification which is a problem for delicate marine ecosystems.

There is therefore a strong imperative to remove the 600 billion tonnes of fossil carbon that we’ve already puffed into the air in just 250 years. This is known as Carbon Dioxide Removal (CDR).

We must work fast to cut our carbon emissions and at the same time we should explore as many climate engineering options as possible, simultaneously. However while reflecting sunlight may be an idea that buys us some time it is absolutely not a solution for climate change and it is still vital that we cut our emissions – we can’t use climate engineering as a get-out clause.

Hugh Hunt, Reader in Engineering Dynamics, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Hugh Hunt (Department of Engineering) discusses whether we could directly engineer the climate and refreeze the poles.

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Modelling impacts of a warming world

lw355 — Wed, 03 Oct 2012 13:37:36 +0000

How different will the world be if it’s 2°C, 3°C or 4°C warmer? Ask this question of the multitude of different climate change impact models – each built by researchers interested in different aspects of global warming – and the likelihood is that you will get a multitude of answers. Modelling the global impact of climate change is an extremely complex process, and yet it’s absolutely essential if policy makers are to understand the consequences tomorrow of emissions policies adopted today.

Earlier this year, an international group of researchers initiated a joint project to attempt the first systematic quantification of some of the uncertainties surrounding climate change impacts to agriculture, health, biomes and water. Uncertainties such as: to what extent will the world’s vegetation change? Which regions will succumb to drought or flood? What will be the impact on global food crops? And how will the spread of human diseases be affected?

̽��ֱ��Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), coordinated by the Potsdam Institute for Climate Impact Research in Germany and the International Institute for Applied Systems Analysis in Austria, involves two- dozen research groups from eight countries.

Dr Andrew Friend from Cambridge’s Department of Geography is coordinating the analysis of results concerning changes to the world’s biomes – the communities of plants, animals and soil organisms that are characterised by a similar structure and climatic requirement.

It’s a fast-track programme. All of the teams are working to a tight deadline and, by January 2013, they hope to be ready to publish their findings on the likely impacts of climate change predictions. ̽��ֱ��collective results will contribute towards the next report of the Intergovernmental Panel on Climate Change (IPCC), the leading international body that provides a clear scientific view on the current state of knowledge in climate change and its potential environmental and socioeconomic impacts.

Each group is using their own model, together with the very latest climate predictions produced by leading climate modelling groups around the world, to run comparable simulations for four different warming scenarios – conservative, drastic and two in between – from 1950 to 2099.

For Friend, this means Hybrid, the model he first developed 15 years ago. At its heart is a set of equations that dynamically model global vegetation: “It works by simulating the dynamics of individual trees and an underlying herbaceous layer. You assume the plants compete within patches, and then scale these up to 50-km grid boxes. We use data to work out the mathematics of how the plant grows – how it photosynthesises, takes-up carbon and nitrogen, competes with other plants, and is affected by soil nutrients and water – and we do this for different vegetation types. Effectively, the whole of the land surface is understood in 2,500 km² portions. We then input real climate data up to the present and look at what might happen every 30 minutes to 2099.”

For the most extreme scenario of climate change being modelled, Friend expects to see significant impact: “this scenario could show the whole of the Amazon rainforest disappearing this century, depending on the climate model. ̽��ֱ��circumpolar Boreal forest, which began to emerge at the end of the last ice age, could migrate into the tundra and perish at its southern limit. By contrast, Russia may benefit from an increased ability to grow crops in regions that were previously too cold, and this greater productivity would help absorb atmospheric carbon.”

Modelling impacts is complex, as Friend explained: “the increase in CO₂ in the atmosphere from the burning of fossil fuels creates global warming. CO₂ can act on vegetation, increasing their rate of photosynthesis and therefore productivity. However, in heatwaves, ecosystems can emit more CO₂ than they absorb from the atmosphere. We saw this in the 2003 European heatwave when temperatures rose 6°C above mean temperatures and the amount of CO₂ produced was sufficient to reverse the effect of four years of net ecosystem carbon sequestration.”

One of the greatest uncertainties in climate change is the feedback from changes in terrestrial carbon cycling. “Many scientists think that if soil warms it will release carbon because of the increased breakdown of dead organic matter by bacteria and fungi,” added Friend. “But there’s a lot of debate over whether this stimulation will be sustained over a long time – if it is, then you end up releasing enormous amounts of CO₂ into the atmosphere, causing further global warming.”

Working with PhD student Rozenn Keribin, Friend is using Darwin, the ̽��ֱ��’s High Performance Computing Service’s supercomputer, to run the simulations; what takes a month to perform on a PC can be easily accomplished overnight on Darwin.

As the results of each group’s simulations become available over the coming months, the data will be assembled and compared. Friend fully expects that this process will reveal differences: “each equivalent model has its own strengths and weaknesses. That’s why the comparison process is so valuable – no single model is sufficient but together we can reduce the uncertainty.”

Why is this so important? “To make policy you need to understand the impact of decisions,” said Friend. “There hasn’t been a coordinated impacts project for IPCC across sectors before, and now this is covering four key sectors across four climate change scenarios from multiple climate models. ̽��ֱ��idea is to understand at what point the increase in global temperature starts to have serious effects across all the sectors, so that policy makers can weigh up the probable impacts of allowing emissions to go above a certain level, and what mitigation strategies are necessary to avoid significant risk of dangerous climate change.”

For more information, please contact Louise Walsh (louise.walsh@admin.cam.ac.uk) at the ̽��ֱ�� of Cambridge Office of External Affairs and Communications.

A community-driven modelling effort aims to quantify one of the gravest of global uncertainties: the impact of global warming on the world’s food, health, vegetation and water.

Each model has its own strengths and weaknesses. That’s why the comparison process is so valuable – no single model is sufficient but together we can reduce the uncertainty.

Dr Andrew Friend

Andrew Friend

Initial ISI-MIP simulation showing the effects on vegetation productivity at the highest emissions scenario (reduction: red to yellow; increase: green to blue)

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