Leaders of many of the world’s states gather in Paris next month for climate talks, having promised in advance that any agreement will fall well short of the 2 degrees target for avoiding dangerous global warming.
An army of politicians, PR people and diplomats are working to create the impression that, nevertheless, something positive is being done. This balloon of
hype needs to be popped. The precondition for serious action is honesty about the scale, and difficulty, of the problem, and acknowledgement of how far away we are from a solution.
Rising sea levels is a key part of the problem, and recent research on it – that I attempt to summarise and discuss in this article – helps explain the scale of the problem. The bottom line is this: while governments’ promises lag further and further behind targets for climate action set out by the Intergovernment Panel on Climate Change (IPCC), oceanographers and glaciologists are warning that those targets lag further and further behind the science.
The West Antarctic ice sheet is going
A consensus is emerging among oceanographers that the West Antarctic ice sheet – one of the largest blocks of above-sea-level ice – has become unstable and will inevitably collapse. (See “Ice sheets and oceans: some basics”, below.)
The timing of the impact is not immediate, and not clear. The collapse could take anything between 200 and 2000 years to unfold. But the end result is easier to measure: a three-metre rise in sea level, which will make human settlements in which tens of millions of people live uninhabitable.
Satellite observations last year confirmed the accuracy of two separate computer simulations that show the West Antarctic ice sheet “has now entered a state of unstoppable collapse”, climate scientist Anders Levermann wrote last year. Levermann, who is based at the Potsdam Institute for Climate Impact Research, went on:
The planet has entered a new era of irreversible consequences from climate change. The only question now is whether we will do enough to prevent similar developments elsewhere. What the latest findings demonstrate is that crucial parts of the world’s climate system, though massive in size, are so fragile that they can be irremediably disrupted by human activity. It is inevitable that the warmer the world gets, the greater risk that other parts of the Antarctic will reach a similar tipping point; in fact, we now know that the Wilkes Basin in East Antarctica, as big or even bigger than the ice sheet in the West, could be similarly vulnerable.
Rather than reacting to global warming with “gradual and predictable patterns of change”, Levermann went on,
the West Antarctic ice sheet has suddenly “tipped” into a new state. A relatively small amount of melting beneath the Amundsen Sea’s ice shelf has pushed its grounding line to the top of a sub-glacial hill, from which it is now “rolling down”. Simply put, one thermal kick was enough to initiate an internal dynamic that will now continue under its own momentum, regardless of any action that humans might take to prevent it.
It is not completely clear whether humans have caused this, Levermann added – although nothing like it has occurred during the entire 11,500-year Holocene period “before humans started interfering with the planet’s energy balance”. But that’s not the point, in his view. The important thing to recognise is that huge elements of the earth’s climate system can be upset by even a small rise in temperature.
Levermann made his warnings after the publication of a study by researchers at the US space agency NASA, and the University of California Irvine, showing that glaciers in the Amundsen Sea area – the Thwaites glacier, the Pine Island glacier and the Smith-Kohler glacier system – have “passed the point of no return”. (See a NASA press release here, and a strongly-worded blog post by glaciologist Eric Rignot here.)
A second study, by a team led by Ian Joughin of the University of Washington in Seattle, focuses on the Thwaites Glacier, and predicts that it will collapse completely within between 200 and 1000 years. (See university press release here, and report in New Scientist here).
The glaciers will themselves push global average sea level up by 1.2 metres when they melt completely. And because of the way that they keep other parts of the ice sheet in place, their disappearance is likely to destabilise the whole thing. And these grim predictions are not outliers: they fit in with the results of several decades of earlier research (as explained by a NASA fact sheet here).
This month, Levermann and others at Potsdam published a new set of computer simulations of the effects of 60 more years of ice melting at the current rate, which re-confirmed the connection between the ice sheet collapse and a three-metre rise in sea level. (See report in Nature here.)
As a non scientist, I am constantly struck by the huge uncertainties these researchers are forced to deal with. This stuff has so many moving parts. A team at the NASA Goddard Space Flight Centre highlighted this in another paper published this month. They concluded from satellite data that snowfall in mainland Antarctica is making both the continent’s ice sheets larger, not smaller. This puts a question mark against the conclusions, cited in the IPCC’s 5th assessment report in 2013, that Antarctica is already losing land ice overall.
But Jay Zwally, the leader of this research team, emphasised that the results did not contradict the danger posed by long-term ice losses. There are losses and gains, and the only question is when – not whether – the former will
supercede the latter. If the losses keep increasing at the rate they have been doing in the last 20 years, they will “catch up with the long-term gain in East Antarctica within 20 or 30 years”, he said. “I don’t think there will be enough snowfall increase to offset these losses.” (See NASA press release here.)
Moreover, the good news in his team’s results – that Antarctica is apparently taking away 0.23 mm per year from sea level rise, rather than contributing to it – had to be offset with the bad news, he added: the 0.27 mm rise attributed by the IPCC to Antarctica must be coming from elsewhere that is not yet accounted for.
The full picture of inevitable long-term sea rise – over a period between two centuries and two millennia – was brought together in a recent report in the New Scientist. Even in the unlikely event that global warming is limited to 2 degrees above pre-industrial levels, it said, 0.8 metres of sea level rise from thermal expansion, 0.4 metres from mountain glaciers and 3.3 metres from the West Antarctic Ice Sheet is already locked in.
Furthermore, oceanographers say that key glaciers in the Aurora and Wilkes basins in eastern Antarctica are also thinning, albeit very slowly – and not yet irreversibly, as far as they can tell. A loss of all this ice would mean 20 metres of sea level rise. Greenland, the ice from which would add 6 metres to sea level, is also “nearing the point of no return”, the article reports.
That last point was underlined by a study published in Science journal last week, showing that one of Greenald’s large glaciers, Zachariae Isstrom, is now begun to retreat, and will add half a metre to global sea level all by itself at some time in the next few centuries. The study, based on data provided by six space agencies, said the glacier “entered a phase of accelerated retreat in fall 2012”.
Why the IPCC estimates may be too modest
As for timescales relevant to us, and our children, grandchildren and great grandchildren – i.e. the 85 years remaining of this century – the consensus among oceanographers is that estimates used by the IPCC’s report are too conservative.
In its 5th assessment report published in 2013, the IPCC increased its estimates of “likely” sea level rise during the 21st century, giving a range between 0.26 metres and 0.98 metres. But oceanographers think these figures are still too low.
A survey of 90 sea-level experts from 18 countries showed that they forecast a rise of 40-60 cm by 2100 and 60-100 cm by 2300 if strong measures are taken to limit greenhouse gas emissions. Without such measures, they expect 70-120 cm of sea level rise by 2100 and 2-3 metres by 2300.
The IPCC estimates are based mainly on computer models, but these often can not simply answer complex problems, climate scientist Stefan Rahmstorf argued on the Real Climate blog. “Experts form their views on a topic from
the totality of their expertise – which includes knowledge of observational findings and model results, as well as their understanding of the methodological strengths and weaknesses of the various studies”, he pointed out.
Rahmstorf has argued for years that semi-empirical models, which use past sea-level and temperature data to quantify the likely response of water and ice to higher temperatures, are better bases for prediction than the physics-based models on which the IPCC relies. (See a 2010 comment article here, and a (more technical!) scientific paper here.)
The estimates of sea-level rise cited in the IPCC’s 2013 report were higher than those in its 2007 report (for the “moderate” scenario, 60% higher). But they were still lower than those generated by semi-empirical models – one of the reasons the New York Times commented that the IPCC was “bending over backwards to be scientifically conservative”.
In another blog post, Rahmstorf argued that, for millions of people living in coastal areas, valuable time had already been lost. “Even with the most stringent mitigation efforts”, sea level rise could exceed 60 cm by 2100 – and it is “basically too late to implement measures that would very likely prevent half a meter rise in sea level”. [Date has been corrected. It said 2011 due to a typing mistake.]
Early action is the key to avoiding higher sea level rise, he continued. “This is where the ‘conservative’ estimates of the IPCC, seen by some as a virtue, have lulled policy makers into a false sense of security, with the price having to be paid later by those living in vulnerable coastal areas.”
In the run-up to the Paris talks, a group of 17 authors led by James Hansen of Columbia university (who journalists often label “the world’s leading climate scientist”) weighed in with a paper (on open access here), arguing that the new research on melting ice is one of several factors that make even the IPCC’s 2 degrees global warming target too high to fend off potential disasters. In particular Hansen and co warns of potential feedbacks, i.e. effects of warming that themselves accelerate the warming process.
Some researchers say that Hansen’s conclusions run ahead of what can be deduced from the evidence (reported e.g. in the Washington Post here). Others think the paper acts as a welcome counterweight to the IPCC’s inbuilt caution.
The impact of rising sea-levels, including coastal erosion, increased danger of flooding and salination of agricultural land, are hard to quantify. They make most sense when considered together with other effects of global warming
such as the growing frequency of storms and the ruination of agricultural land, and effects of other environmental stresses such as freshwater shortages.
A group of UK-based researchers estimated the impacts of global warming assuming a 2.2 degree rise in temperature and a global mean sea level rise of 16 centimetres, by 2050. That would mean 450 million people being exposed to a doubled risk of floods and 1.3 million more than now being flooded each year. The coastal flood risk would be highest in Asia and east Africa, and wetland losses would be heaviest in the Mediterranean and north America.
The US Union of Concerned Scientists’ Climate Hot Spots site is a good information resource. It summarises research on some highly vulnerable regions, e.g. the Ganges-Brahmaputra Delta in Bangladesh, where 3 million people are likely to be directly affected by rising sea levels by 2050, and many more due to salination of agricultural land. On flood risk, the UCS site highlights that the risk to New York currently defined as once-a-century will become twice as likely by 2050 and up to 10 times as likely by 2100; a recent research paper from Potsdam highlighted that – without strong mitigation measures – unabated global warming would result in flooding of up to 20 million homes in the US, including 21 cities with population of more than 100,000.
The impacts in south-east and south Asia, and sub-Saharan Africa, are analysed in a recent World Bank report. Coastal regions near the equator, of which all these three regions have many, are expected to face sea-level rise of 10-15% higher than the global mean. “Coupled with storm surges and tropical cyclones, this increase is proejcted to have devastating impacts on coastal systems”, the report says.
It would be easy to tack some pat political “solutions” on the end of an article like this. I won’t. Here instead are some observations that, as a socialist, I think might help us get our heads round this.
First, what the danger of the West Antarctic Ice Sheet collapsing reminds us is that humans collectively have the ability, and technology, to disrupt huge bits of the earth’s natural systems, with devastating future consequences. Society under its present elite has failed, disastrously, to use this ability responsibly. This is exactly the sort of “tipping point” that climate scientists have been warning of for years – a new type of danger. There is no simple political solution to three metres and more of sea-level rise, however far in the future it happens.
Second, there are timing issues. The current impacts of rising sea levels – such as the crisis in small island states, and the greater likelihood of disasters such as Hurricane Katrina’s damage to New Orleans – have been caused by past greenhouse gas emissions. Past and present emissions will leave future generations to deal with the melting of West Antarctic ice; Andreas Levermann and his colleagues say this is damage already done. Future emissions have the potential to do even more spectacular damage.
Third, the impacts accentuate the divisions between rich and poor countries. Rich countries’ governments build flood barriers and relocate buildings (although not even-handedly, as New Orleans showed), and keep out refugees. People in poor countries, and their agricultural systems, suffer far, far more severe effects.
Fourth, the failure of the world’s governments to confront these problems is a historic failure of states, and of the world system of states organised through the UN (as I argued here). GL, 23 November 2015.
Ice sheets and oceans: some basics
There are three physical factors that push up global average sea level: (i) thermal expansion of warming ocean water; (ii) the addition of new water from glaciers, ice caps and the ice sheets of Greenland and Antarctica; and (iii) the addition of new water from land surface run-off.
The main cause of thermal expansion and of ice melt is global warming. The main cause of that, in turn, is the emission of greenhouse gases into the atmosphere by fossil fuel consumption and other aspects of human economic activity.
If all the ice in (a) Antarctica, (b) Greenland and (c) the glaciers and ice caps melted, it would make global sea level rise by about (a) 57 metres, (b) 8 metres and (c) 0.7 metres. The ice in the West Antarctic ice sheet alone would add 3 metres or more to global sea level.
The best scientific estimates are that the process is accelerating. In the 20th century up to 1990, global average sea level rose by about 1.7 millimetres per year. The IPCC says it is likely that between 1993 and 2010, it rose by about 3.2 millimetres per year (a rate that equates to 0.32 metres per century).
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