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Rising seas culprit: ice or heat?

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Melting ice off Greenland (Pic: I.Quaile)

My attention was caught this week by a study that ascertained that thermal expansion accounts for a much greater share of sea level rise than previously thought. In fact, quite a few journalists got the message wrong. They thought the researchers had found that climate change was causing sea level rise twice as high as previously thought, which would have been quite a sensation. In fact, what the scientists actually found was that the amount of sea level rise that comes from the oceans warming and expanding has been underestimated and is probably about twice as much as previously calculated. There is a clear difference, which does not make the research – using the latest available satellite data – any less interesting.

Since two of the authors of the study are based here in Bonn, I was able to drop in on them and get them to explain their findings and the implications for our Living Planet programme. That will be broadcast in the near future. I also talked to Professor Anders Levermann from the Potsdam Institute for Climate Impact research on the phone, to get the research findings into context.

While physicists understand the workings of thermal expansion in the oceans in general, Levermann told me there is still a lot to learn about how the heat from excess warming is transported in the ocean, which is of key importance to understanding sea level rise, amongst other things. He says the new research will help make models of future sea level rise more accurate.

Roelof Riebroek and Jürgen Kusche, University of Bonn

Roelof Riebroek and Jürgen Kusche, University of Bonn (Pic: I.Quaile)

The Bonn researchers explained to me how satellite technology has made huge improvements in the collection of data, especially relating to the very deep areas of the ocean, which are very difficult to reach with conventional measuring gauges. Professor Kusche told me he would like to see the results of the study, published in the Proceedings of the National Academy of Sciences, being used by governments and coastal planners, as sea level rise will affect a large number of people living in coastal areas in the not-too-distant future. Warming seas are also linked to the occurence of storms, making the findings doubly relevant to those involved in protecting coastal areas.

From an Iceblogger point of view, I was keen to know whether the knowledge about the amount of sea level rise ascribed to  thermal expansion had any implications for the role played by melting ice in raising sea level. If thermal expansion is accounting for a higher share of the sea level rise, is melting ice from Greenland and Antarctica accounting for less? I put that question first to Professor Kusche.

“We think that less of the sea level rise is coming from melting ice and glaciers, that’s actually true,” he answered. He said he and his colleagues had done a very thorough re-analysis of all the measurements available over the last 12 or 13 years, “and we are pretty sure that our numbers are correct”.

Rietbroek came in that that point: “Less, but not that much less. If you look at pubished literature and estimates of glacier melting, and try to add those up, you won’t be that far away from what we get. So the melting of glaciers is not that different from what’s been found previously”, he added.

Ice melts from above and below

Climate change melts ice – from above and below(Pic:I.Quaile)

I put the same question to Professor Levermann from PIK, who runs an ice sheet model for the Antarctic and was lead author of the IPCC chapter on sea level change. He explained to me that the various contributions to sea level rise are measured and modelled separately by different teams of experts in particular fields. The models all have a wide range of possible variation. He told me there is still some uncertainty in the distribution of the “sea level rise budget” between thermal expansion, ice sheet melt, mountain glacier melt and groundwater mining. While the latest findings on thermal expansion could potentially shift the relative contributions and are important for improving models to project future sea level rise more accurately, they do not change the validity of predictions relating to the amount of ice going into the ocean.

Ultimately, Levermann says, one of the IPCC statements with the highest certainty is that sea level will continue to rise for centuries to come. He was one of the authors of yet another study  published in Nature Climate Change this past week, led by Peter Clark from the Oregon State University. It affirms that our greenhouse gas emissions today produce climate change commitments for many centuries to millenia. Unless the Paris climate agreement is put into practice asap and we reach zero or negative emissions, up to 20 percent of the world’s population will find itself living in areas that may have to be abandoned.

We are, indeed, living in the Anthropocene. Recently, I interviewed a scientist who found that we have already postponed the next ice age by 50,000 years through our fossil fuel emissions. The latest sea level study indicates that the next few decades offer a brief window of opportunity to avoid increased ice loss from Antarctica and “large-scale and potentially catastrophic climate change that will extend longer than the entire history of human civilization thus far”.

 

 

Date

February 12, 2016 | 2:50 pm

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Anthropocene: No ice age – more blizzards?

 

Heavy snow - not just fun (Pic: I.Quaile)

Heavy snow – not all fun (Pic: I.Quaile)

If you are sitting somewhere on the East Coast of the USA, struggling to cope with 30 inches of snow, you might be forgiven for reacting with relief to a report released by the Potsdam Institute for Climate Impact Research (PIK) indicating human-made climate change is suppressing the next ice age. With a wink in your eye, you might be very grateful that these extreme conditions are only going to last for a few days and not become the everyday normality of a new ice age.

There are those (but increasingly few of them) who might even thank the fossil fuels industries for averting a scenario like “The Day after Tomorrow” and ensuring that the relatively comfortable interglacial in which we live is likely to continue for the next 100,000 years. That is the conclusion of the study published in the scientific journal Nature.

The problem is that postponing an ice-age illustrates that human interference with natural climate cycles over a relatively short time has the potential to change the world for a hundred thousand years to come, with all the problems that come with it. And given that the increase in extreme weather events like the US snowstorm is highly probably related to anthropogenic climate change, perhaps an ice age in 50,000 years would be the lesser evil.

Burn fossil fuels, suppress the ice age

Using complex models to try to find out which factors influenced the last eight glacial cycles in earth history and what is likely to lie ahead of us, the scientists found that as well as astronomical factors like the earth’s position in relation to the sun in different stages of its orbit, the CO2 concentration in the atmosphere is a key factor.

I talked to physicist and earth systems modeler Andrey Ganopolski, lead author of the study to find out more about the research and the background.

Listen to the interview.

Ganopolski is a physicist and climate modeler. (Pic: PIK)

Ganopolski is a physicist and climate modeler. (Pic: PIK)

According to Milankovich’s theory, a new ice age should occur when the earth is far away from the sun and summer is colder than usual in the northern hemisphere, at high latitudes in Canada and northern Europe. These are the areas where big ice sheets can grow. At the moment, Ganopolski explained, we have a situation where our summer occurs when the earth is far from the sun. So in principle, we have the conditions when a new ice age can potentially start. He and his colleagues wanted to understand why we are not living in an ice age when astronomically, the conditions are just right to move towards a new ice age.

Meddling with the planet

They come to the conclusion that naturally, without any anthropogenic influence, we would expect the new ice age to start around 50,000 years from now. That would mean that this interglacial, the Holocene, in which we live now, would already be unusually long. In the past, an interglacial lasted only 10 or 20,000 years, but this one is expected to last for 60,000 years.

arctic emissions

Greenhouse gas emissions are transforming all areas of the planet. (Pic: I.Quaile)

But our emissions of greenhouse gases are postponing this even further. Relatively large anthropogenic greenhouse gas emissions – say two to three times what we already emitted – would, according to the scientists’ model, additionally postpone the next ice age, so that it would only start 100, 000 years from now, so we would completely skip one glacial cycle, which never happened in the last three million years.

Humankind as a geological force

Now regardless of whether you are a fan of ice and snow or one of those who say they can happily live without any more ice ages, the study’s findings illustrate just how long anthropogenic influence on climate will continue. Humanity, it seems, has become a geological force that is able to suppress the beginning of the next ice age, according to the PIK experts. Human behavior is changing the natural cycles that have shaped the global environment and human evolution.

Over the last 3 million years, glacial cycles were more or less regular. Most of the evolution of humans occurred during those last three million years. Ganopolski says humans can be seen as a kind of product of glacial cycles, because the conditions were probably right to increase the size of our brain, because we had to be clever to survive in such a variable climate.

Melting ice, north and south? (Photo: I Quaile)

Melting ice, north and south? (Photo: I Quaile)

Who cares?

But given that it is easier and pleasanter to live in non ice-age conditions, there is still an understandable tendency to respond to the ice-age-postponement announcement with: “so what?”

Ganopolski argues one reason the study is significant is that it does away with the arguments of some climate skeptics who have argued that warming the atmosphere by burning fossil fuels is not a bad thing, because it could avert an “imminent” ice age (a theory first made popular around thirty years ago, he says). Since the research indicates there is none on the horizon for more than 50,000 years anyway, this is nonsense, says Ganopolski.

But the main reason the research findings deserve attention, he says, is that they show we can affect the climate for up to a hundred thousand years. He believes a lot of people think if we stop using fossil fuels tomorrow or the day after, everything will be fine. In fact, anthropogenic carbon dioxide will stay in the atmosphere for an extremely long time. “That means we are affecting earth’s future on a geological time scale”, he says.

Whether the next ice age comes in 50,000 or 100,000 years may seem irrelevant to a lot of people, faced with the concerns of life today. But the effects of our warming the globe are already being felt and will have considerable implications well before that, Ganopolski reminds us. He says the new study just shows how massive our interference with the earth’s systems is, and backs up the need to take action now to cut greenhouse gas emissions.

Measuring CO2 in Ny Alesund, Svalbard, Spitzbergen

Rising CO2 emissions are influencing glacial patterns (Measuring station on Svalbard, Pic. I. Quaile)

Greenland and Antarctic in the Anthropocene

He mentions the research also deals with Greenland and Antarctica:

“What we show is that even with the CO2 concentration we have already, we can expect that a substantial fraction of these ice sheets will melt. So obviously, in this respect, any further increase of CO2 will have even more negative effects”.

Sea level rise, ocean acidification, changing food supplies, floods, droughts…and, yes, even more of those extreme blizzards, fuelled, paradoxically, by warming seas…maybe there is more to this delaying the ice age business than first seemed.

So are we living in the “Anthropocene”, i.e. an era in which not nature but humankind is determining the shape of the world we live in now and for centuries to come? Ganopolski and his colleagues say yes. He stresses what we are doing to the climate and the speed at which it is happening represent unprecedented, substantial deviation from the natural course of things.

“So if you continue to emit a substantial amount of carbon dioxide, the Anthropocene will last for hundreds of thousands of years, before systems return to anything like “normal” conditions”, he says.

Another  study published in Nature  today provides further evidence that human intervention is responsible for the annual heat records that have been in the news so often recently they run the risk of losing their news value. Ganopolski’s PIK colleague Stefan Rahmstorf, one of the authors, says the heat records, with 13 of the last 15 years the warmest since records began, can no longer be explained by natural climate variation. But they can be explained by human-induced climate change.

But is there any point in making potentially uncomfortable changes to the way we live today if we have already changed the atmosphere so massively, for such a long time to come? Ganopolski stresses the extent and speed of the changes and impacts are no grounds for resignation:

“There is no justification for making the climate even warmer than it is. It is a matter of how much CO2 we will emit into the atmosphere. Basically, it will affect all generations, and if we care about them, we should stop using fossil fuel as soon as possible.”

Sounds sensible to me.

Date

January 25, 2016 | 3:55 pm

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Greenland ice a speedy chute to rising seas?

Greenland ice sheet is discharging ice into the ocean at an alarming rate. (Pic: I.Quaile)

Greenland ice sheet is discharging ice into the ocean at an alarming rate. (Pic: I.Quaile)

As I checked through the news agencies to keep tabs on what’s been happening with Greenland as 2016 kicks off, the only agency piece I came across is a German story (on AFPD) on how climate change is apparently bringing the world’s biggest island an “economic upswing”. New fish species off the coast, better conditions for agriculture and exportable powdered rock from retreating glaciers are listed amongst the benefits.

No mention of a study published in Nature Climate Change this week showing that recent atmospheric warming – especially the exceptional summers in 2010 and 2012 – are reducing the ability of some layers of the giant ice sheet to store meltwater. That, in turn, can mean runoff is released into the ocean faster than previously assumed, rushing down a kind of icy chute. Clearly, this has considerable implications for global sea level rise.

Snow sponge

Approximately half of Greenland’s current annual mass loss is attributed to runoff from surface melt. At higher elevations, the melt does not necessarily equal runoff, because meltwater can refreeze in the porous snow and firn near the surface. Horst Machguth from the Geological Survey of Denmark and Greenland, the lead author of the study, explains the background in a news release by CIRES, the Cooperative Institute for Research on Environment Sciences, Boulder Colorado:  “The near-surface of the large ice sheet interior is comprised of snow that is slowly being converted into glacier ice. This porous firn layer can be up to 80 m thick,” he writes. Recent studies indicated that this firn is an important buffer against contributing to sea level rise for decades to come, because it absorbs and stores the meltwater like a sponge, refreezing it to form ice layers as it percolates down from the ice sheet surface. But the authors say the new study shows this may not be the case.

VIEW: Animated graphic illustrating the “sponge” effect on the Greenland Ice Sheet by NASA and CIRES

After the Greenland Ice Sheet was hit by a series of warm summers, it was unknown how the firn reacted to exceptional amounts of meltwater, says Machgut. The research aimed to clarify whether the firn was indeed capable of retaining the meltwater, or whether the sponge had been “overwhelmed” by all the extra water.

Meltpool on the Greenland ice sheet (Pic: I.Quaile)

Meltpool on the Greenland ice sheet (Pic: I.Quaile)

Icy chute

The scientists drilled cores to sample the firn at sites where similar cores had been drilled 15 to 20 years ago. They found that the amount of refrozen ice layers in the firn had increased substantially over the past two decades in many places, but not everywhere. Cores drilled at lower elevations suggested the recent exceptional meltwater amounts had only trickled through to shallow depths within the firn, conglomerating into massive ice layers directly below the ice sheet surface.

“It appears that the firn was overwhelmed by the melt to a degree where so many ice lenses had formed that they started to hinder percolation of further meltwater. Initially small ice lenses grew to form ice layers of several meters in thickness that act as a lid on top of otherwise sponge-like firn. Radar measurements identified that these massive ice lenses were continuous over tens of kilometres,” says Dirk van As, a co-author of the study from the Geological Survey. “Surface meltwater wants to refreeze in firn locally, which it does at higher elevation, but at lower elevations it hits that lid of ice and is forced to stay at the surface where it cumulates.”

Satellite images show that meltwater then formed rivers on the surface flowing towards the margin of the ice sheet.

Meltwater trickles over Greenland ice sheet (Pic: I.Quaile)

Aerial view: Meltwater trickles over Greenland ice sheet (Pic: I.Quaile)

More data required

“In contrast to storing meltwater in porous firn, this mechanism increases runoff from the ice sheet,” says CIRES researcher Mike MacFerrin, a second author on the study. “This process has not previously been observed in Greenland. The extent of this ice lid capping the ice sheet firn remains unknown. For this reason, the total amount of additional ice sheet runoff associated with this newly observed process cannot yet be quantified.”

The scientists are now combining their core data with radar measurements from NASA, which cover the entire ice sheet. They say similar changes in firn structure have been observed on various ice caps in the neighbouring Canadian Arctic, which indicates the phenomenon could be widespread in Greenland. Only west Greenland was covered by the new study.

Greenland ice: taking the measure (Pic: I.Quaile)

Greenland ice: Iceblogger taking the measure (Pic: I.Quaile)

The Greenland ice sheet is already a great concern, with the melting ice rate increasing continually as the atmosphere and the oceans warm. As well as contributing to rising sea levels, the increase in runoff from the ice sheet could also result in feedback processes which could lead to even more melt in the future. The water running down the ice sheet can create darker, slushy channels, the scientists say, which can reduce the albedo effect of the ice sheet, its ability to reflect sunlight away from its surface. As more sunlight is absorbed instead of being reflected off, the surface temperature could warm further.

Given the huge significance of the Greenland ice sheet in terms of global sea level rise and its role in the global climate system, the findings of this study deserve a little more attention than being confined to the publications of the scientific communities.

But maybe potatoes from the “ice island” and mackerel and tuna off its snow-tipped coasts make for more striking headlines?

Date

January 6, 2016 | 3:09 pm

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Can Paris avert climate threat to cryosphere?

 

Meltpool on the Greenland ice sheet (Pic: I.Quaile)

Meltpool on the Greenland ice sheet (Pic: I.Quaile)

To those of us who work on polar subjects, there is no question about the relevance of the cryosphere to the annual UN climate negotiations. But in the run-up to the annual mega-event – especially in a year dubbed by some to be the “last chance” for climate – it was not easy to get attention for the Arctic, Antarctic and high-altitude peaks and glaciers of the world.

I had a discussion with some of my colleagues who focus on Africa and Asia. With problems like political unrest, wars, famine and drought to cope with, the fate of polar bears, one told me, is completely irrelevant.

You could say this colleague is suffering from a kind of tunnel vision. But it also prompts me to wonder whether the way we communicate the threat of climate change is partly to blame.

Not just polar bears

Earlier this week I read about a study indicating that people were more likely to donate to campaigns which focus on people, on social injustice rather than on conservation and environmental degradation. Somehow, we journalists have to make the connection between the two. When you remind people that increasing sea levels caused to a large extent by changes in our ice sheets pose a huge threat not only to small island states but to many of the world’s megacities, the cryosphere takes on a new relevance. Not to mention the fact that the ice, snow and permafrost covered regions of our planet play a major role in regulating the world’s climate and water supplies.

What life goes on beneath the Svalbard sea ice? (Pic I.Quaile)

Ice off Svalbard  (Pic I.Quaile)

One organization that works to bring the attention of delegates at the UN climate talks to our icy regions is the International Cryosphere Climate Initiative, ICCI. In time for this year’s COP21, it commissioned a report from leading scientists: “Thresholds and closing windows. Risks of irreversible cryosphere climate change”. The report summarizes the levels of risk in five key areas: ice sheets loss and related sea-level rise, polar ocean acidification, land glacier loss, permafrost melt, and the loss of Arctic summer sea ice. The report is based on the last IPCC assessment plus literature published in the three years since.

Bringing the ice closer

Pam Pearson is the director and founder of ICCI. I have interviewed her on various occasions, including during visits she made to Bonn, the home of the UNFCCC, to brief delegates. This time we were not able to meet in person, but we have been in Email contact. I asked her how difficult it was to arouse interest within the negotiations at the moment, with so much going on. She told me it was difficult mainly because very few people globally actually live near cryosphere.

“Yet we are all deeply connected to these regions, because of their role in the Earth climate system — especially through sea-level rise, water resources from land glaciers, and permafrost release that will make it harder to meet carbon budgets. “

The Arctic, parts of Antarctica and many mountain regions have already warmed two to three times faster than the rest of the planet, between 2 and 3.5 degrees Celsius up on pre-industrial levels. Climate change is also affecting high altitude areas such as the Himalayas and the Andes, where seasonal glacier melt provides water for drinking and irrigation, especially in dry periods.

When the outside risk becomes the norm

The changes are far more extreme than those forecast in even the most pessimistic scenarios of a few years ago.  In the IPCC’s 2007 Fourth Assessment, the outer extreme estimate for sea level rise (mostly from glacier ice melt) was about one meter by the end of this century.  Today, the experts say even if we could halt warming now, it would be impossible to avoid sea-level rise of one meter from glaciers, ice sheets and the natural expansion of warming waters, within the next two hundred years. Most scientists also agree that the West Antarctic ice sheet has already been destabilized by warming to the extent where this probably cannot be halted, which will increase sea level further.

Pam Pearson, Director of ICCI. (Pic: I.Quaile)

Pam Pearson, Director of ICCI. (Pic: I.Quaile)

Pearson used to be a climate negotiator herself, so she knows the pressures and constraints. She told me that while participants in the climate conferences were broadly aware of issues like ice melt at the poles and on high-altitude glaciers, they tended to lack awareness of two key aspects:

“First, that we have already passed, or are close to passing temperature levels that will cause certain processes to begin; and second, that some of these processes cannot be stopped once they get started.”

She says a “sense of urgency” is lacking, and stresses that although some of the most damaging consequences will only occur in hundreds or even thousands of years, they will be determined by our actions or inactions in the coming few decades. That includes the 2020-30 commitment period that is the focus of the agreement being worked on in Paris Pearson stresses.

The cryosphere needs more ambitious targets

The report analyses the implications of the INDCs, or current pledges put on the table by the countries of the world for the Paris climate talks. The scientists come to the conclusion that these will not be enough to prevent the onset of many irreversible cryosphere processes.

Even the two-degree pathway agreed by the international community translates into a peak cryosphere temperature of between 4 and 7 degrees above pre-industrial levels, according to the ice experts. Yet the UN and others say current commitments would lead to global temperatures 2.7 to 3.5 degrees Celsius above pre-industrial levels by 2100, rising later to between 3.4 and 4.2 degrees. The peak in global carbon emissions would occur well after 2050. The associated temperatures would trigger permanent changes in our ice and snow that cannot be reversed, including the complete loss of most mountain glaciers, the complete loss of portions of West Antarctica’s Ice Sheets and parts of Greenland. This would ultimately equate to an unstoppable sea level rise of a minimum four to ten meters, the scientists find.

Greenland's glaciers are all ready discharging huge amounts of ice into the ocean (I.Quaile)

Greenland’s glaciers are already discharging huge amounts of ice into the ocean (I.Quaile)

In addition, the increase of CO2 being absorbed in the Southern Ocean around Antarctica and the Arctic Ocean is turning the water more acidic and so threatening fisheries, marine ecosystems and species.

Another of the key issues which is often neglected is that of permafrost. About a quarter of the Northern Hemisphere’s land area contains ground that remains frozen throughout the year. This holds vast amounts of ancient organic carbon. So when it thaws, carbon dioxide and methane are released, which fuel further warming. Even a temperature rise of 1.5 degrees could result in a 30% loss of near-surface permafrost. This would mean 50 Gigatonnes of additional carbon emissions by 2100. Given that the total carbon budget allocated to a two-degree temperature rise is only 275 Gigatonnes, that would be a huge factor. The ICCI experts say this thaw would not be reversible, except on geological time scales.

Dwindling Arctic sea ice

Arctic summer sea ice has declined rapidly, especially since 2000. Only about half the sea ice survives the summer today compared to 1950. This is “both a result and a cause of overall Arctic and global warming”, according to the ICCI report. White ice reflects heat into space. When it melts, it is replaced by dark water, which absorbs the heat, exacerbating warming further.

The Arctic sea ice has a tempering effect on global temperatures and weather patterns. It would only be possible to reverse the disappearance of the ice in summer with a return to regular global temperatures of 1 to 2 degrees above pre-industrial times, according to the report.

Andes and Himalayas

Receding mountain glaciers in the European Alps, American Rockies, Andes and East Africa were among the first identified, visible impacts of climate change, originally from natural factors. Sometime in the past 50 years, anthropogenic climate change surpassed natural warming as the main driver of retreat, and caused about two-thirds of glacier melt between 1991 and 2010, according to the ICCI report.

Glaciers - beautiful but highly endangered, like this one I visited in the Swiss alps. (Pic. I.Quaile)

Glaciers – beautiful but highly endangered, like this one I visit regularly  in the Swiss alps. (Pic. I.Quaile)

Glaciers are important to nearby communities as a source of water for drinking or irrigation. Some are especially important in dry seasons, heat waves and droughts. Melting glaciers provide an increase in water for a limited time. But ultimately, the lack of water could make traditional agriculture impossible in some regions of the Himalayas or the Andes.

So unless governments in Paris move fast to increase their commitments and bring the deadlines for emissions reductions forward, the windows to prevent some of these irreversible impacts on the polar and high mountain regions may close during the 2020-2030 commitment period.

It is not too late

However, the scientists stress that it is still possible to reduce emissions to the required level, if the political will becomes strong enough. Pam Pearson says the world has to get onto the path towards the two-degree goal now. Like many experts, she says this in itself is risky enough for the cryosphere, and a 1.5 degree pathway would be safer:

“So if countries indeed agree with UNFCCC chief Christiana Figueres’ proposal to meet every five years to strengthen INDCs, moving onto these lower-temperature pathways should be a concrete goal.  Perhaps even more important, I understand the French COP presidency may be aiming at strengthening actions PRIOR to 2020, in the 2015-2020 period. This kind of earlier action is really vital, and will make the job of keeping temperatures as low as possible easier”
Without much more ambitious targets, the ICCI study concludes it will be “close to impossible” to avoid rapid deterioration of our snow and ice regions.

The challenge is to make the delegates in Paris understand that that does not just mean cosmetic changes to distant parts of the globe, but that it would also destabilize the global climate, displace millions of people and endanger food and water supplies in many parts of the world.

 

 

 

 

Date

December 1, 2015 | 3:00 pm

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Can we still avert irreversible ice sheet melt?

IQ on ice

Walking on the Greenland ice sheet (Pic: I.Quaile)

 

Earlier this week, I was able to follow up my last talk with Professor Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK), after he returned from the Paris climate science forum.  After the publication of the study he was involved in on paleoclimatic data linking global temperature with sea level rise, and having heard his views on the science consensus ahead of the December UN summit in Paris, I wanted to know how he views the prospects for the polar ice sheets.

A question I return to often is whether anything we do to reduce emissions from now onwards – given that huge damage has already been done by our fossil fuel emissions and that the CO2 will remain in the atmosphere for a very long time to come –  can prevent the ice sheets in the Antarctic and Greenland from reaching a “tipping point”.

Professor Rahmstorf gives this definition of a “tipping point” – which can mean different things to different people in different contexts:

“Climate tipping points are points of no return, where you cannot stop a process that has been set in motion. It’s a bit analogous to the situation where you are sitting in a rowing boat and you lean over a bit to one aside and not much happens. Then you lean a bit more and a tipping point comes where the boat simply tips over. One of these points of no return is with our continental ice sheets, where their further melt-down becomes inevitable and unstoppable. And we have to realize that we have enough continental ice on this planet to raise global sea level by more than 60 metres. That means we cannot afford to lose even a very small fraction of that ice without drowning coastal cities and small island nations.”

The Sermeq Kujualleq glacier discharges icebergs into the sea (I. Quaile, Ilulissat 2009)

The Sermeq Kujualleq glacier discharges icebergs into the sea (I. Quaile, Ilulissat 2009)

Is the boat still afloat?

But, of course, we are already losing ice at a worrying rate. Rahmstorf cites recent research showing that at least a part of the West Antarctic ice sheet has already been destabilized.

“We probably have already crossed the tipping point for a part of West Antarctica. That is probably going to already commit us to about three metres of sea level rise.”

Of course this is not likely to happen in the very near future. But the problem with the tipping points is, of course, that there is no going back, as Rahmstorf explains:

“Sea level has already risen 20 centimetres globally since the late 19th century, due to modern global warming, which is very basic physics. It’s melting continental ice sheets. And also the oceans are being heated up, which expands the ocean water, because warm water takes up more space. And by the year 2100, with unmitigated emissions, we are looking at one meter of sea level rise, which already, for vulnerable coastal areas like delta regions, like Bangladesh for example, will dramatically increase the storm surge risk. But sea level rise will not stop in the year 2100, because the ice sheets are actually quite slow to melt, and within the next decades, we will be causing a long-term sea level rise commitment by several metres for every degree of global warming that we cause.”

Greenland – and Miami, St. Petersburg, Bangladesh…

Record melting appears to be happening on Greenland at the moment. I asked Rahmstorf how safe the world’s biggest island and the largest area of freshwater ice in the northern hemisphere (See also the Ice Island in Pictures) is from reaching a point of no return. He wasn’t able to give a reassuring answer:

“We don’t know exactly where the tipping point is for the Greenland ice shield is. The IPPC estimates anywhere between one and four degrees of global warming. We are already at one degree warming, so we may well cross that tipping point in the next decades.

Statue of Liberty Action at the Arctic Sea Ice Edge

Thanks to Greenpeace for this vision of Lady Liberty sinking beneath melting Arctic ice.

In the review of the relation between global temperature and sea level rise from polar ice disintegration I discussed in the last blog post, Rahmstorf and his colleagues found that just a slight further rise in temperature might equate to a rise in global sea level of up to six metres. I asked him what that would mean for the world right now:

“There would be quite a number of large coastal cities I cannot imagine could still be defended.  Think of New York city for example. Or Miami would be one of the first cities to go. St. Petersburg, Alexandria, Manila – you name them. Once you are talking about metres of sea-level rise, the consequences would be quite catastrophic. Especially as it is to be feared that people will not react proactively by move away from the danger zone, but will probably stay in their cities until a major storm surge hits. Like Hurricane Katrina hitting New Orleans, which also was a case where experts had warned for a long time that the city was in danger, once the next hurricane strikes, but people still didn’t act according to the precautionary principle. As they should have, and as we must do to prevent a climatic disaster in future.”

Can we keep the ice chilled?

So what would we have to do to keep sea level in check?

“Emissions would have to be close to zero by mid-century, so we are not talking about small cosmetic adjustments, but a transformation of our energy system, decarbonization, that is getting out of the carbon-based energy system. The good news is that the technologies to do that are available. It’s all about mustering the political will. And, of course, fighting the particular interests which are opposing this transformation.”

Stefen Rahmstorf is not one of those scientists who prefer to sit on the fence and leave the interpretation of his research and their implications up to the politicians. He is convinced only rapid action to stop emissions can prevent catastrophic climate change – including the melt of the polar ice.

I have interviewed him on previous occasions in the last few years. This time, I was surprised by his optimistic stance on whether the international community can still do anything in time to stop global warming from reaching the dangerous level of two degrees (or even one point five, as Rahmstorf and others say would be far preferable):

“There’s still a good chance that a strong agreement coming out of the Paris summit in December could mean we could avoid the Greenland tipping point.  I am cautiously optimistic that Paris will reach a meaningful agreement, not necessarily one that guarantees that we will stay below two degrees global warming, but one that will be seen in hindsight as a real turning point, from where emissions started to fall soon after. The key point is – the sooner we stop global warming, the better the chances are that we avoid future critical tipping points.”

All we need, says Rahmstorf, is the political will to make use of the technologies available, take on the fossil fuels lobby, and clean up our energy system.

Listen to my interview with Stefan Rahmstorf on DW’s Living Planet this week.

Date

July 17, 2015 | 2:57 pm

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