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EXPERT REACTION: Sea level rise expected even under Paris Agreement

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Even if all nations stick to the Paris Agreement targets, we're still in for sea level rise in the coming centuries, according to new models from international researchers including an Australian. They estimate global sea level will rise between 0.7 and 1.2 metres by 2300 assuming the Paris targets are fully met. But for every five-year delay in mitigation efforts, they say another 20 centimetres of sea level rise will be added, emphasising the need for action in the coming decades.

Journal/conference: Nature Communications

Organisation/s: The University of Melbourne, The University of New South Wales, CSIRO, The University of Western Australia, Curtin University, Potsdam Institute for Climate Impact Research, Germany

Funder: AXA Research Fund Postdoctoral Fellowship Programme, European Union’s Horizon 2020 research and innovation programme.

Media Release

From: Springer Nature

Sea-level rises under the Paris Agreement

Sea levels will rise between 0.7 and 1.2 metres by 2300, assuming the Paris Agreement targets are fully met, suggests a new modelling study in Nature Communications. Sea levels will ultimately depend on the pathway of emissions during this century, with an increase of 0.2 metres for every five-year delay in mitigating action post 2020, suggest the authors.

Sea-level rise is a response to several factors, such as thermal expansion of the oceans and ice sheet melt, which respond to climate on different timescales. Even if greenhouse gas emissions ceased today, we are already committed to a rise in sea levels in the coming centuries as a result of such processes. The Paris Agreement is set to limit warming below 2 degrees Celsius and ideally below 1.5 degrees Celsius, but how much sea levels will rise in the coming centuries as a result of mitigating action to achieve such targets has not been quantified.

Matthias Mengel and colleagues present model simulations that show if net-zero greenhouse gas emissions are sustained until 2300, sea levels will rise between 0.7 and 1.2 metres depending on the pathway of emissions during this century. Furthermore, it is unlikely that sea levels will stabilize beyond 2300 even if temperatures are kept below 2 degrees Celsius, due to the inertia of the system.

The study also shows that for every five years of delay in reaching a peak in emissions post 2020, sea-level rise projections for 2300 increase by 0.2 metres. The authors conclude that emissions in the following decades will have a strong influence on sea levels in coming centuries, emphasizing the need for near-term mitigating action to limit the risk of sea-level rise.

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

John Church is a Professor in the Climate Change Research Centre, University of New South Wales.

With the order of 100 million people living within 1 m of current high tide level, the world is vulnerable to rising sea levels. More people are moving to live within the coastal zone, increasing the vulnerable population and infrastructure. Recent sea level data show that the rate of sea level rise is accelerating, further increasing the potential vulnerability.

This paper shows:

  • That, even with the most stringent greenhouse gas mitigation, the central estimate of sea level rise by 2300 is more than 0.7 m and still rising, with a potential rise of twice this amount.  These results mean that adaptation to sea level rise will be essential.
     
  • Delaying mitigation results in a higher projected sea level rise by about 20 cm for every five year delay. Mitigating to achieve net zero carbon dioxide emissions rather than zero greenhouse gas emissions results in a substantially higher central value of projected sea level rise, with a potential rise of metres by 2300. To avoid larger sea level rises, mitigation is urgent. 
     

Under the Paris Agreement, current mitigation commitments by nations to 2030 are at the upper level of the emission scenarios considered. Mitigation efforts will need to be increased significantly and urgently if a rise of more than 1 metre sea level rise by 2300 is to be avoided.

Last updated: 20 Feb 2018 4:36pm
Dr Xuebin Zhang is a Senior Research Scientist for CSIRO Oceans and Atmosphere

Global warming and sea-level rise are two important indicators of anthropogenic climate changes, but the ocean and atmosphere respond very differently to greenhouse gases emission mitigation, e.g., as proposed under the Paris Agreement.

The atmosphere can respond very quickly to emission cuts and global mean surface temperature can stabilise or even reduce, while the ocean takes a much slower pace and adjusts on the timescale of a few centuries, which means that global sea level is guaranteed to rise in coming centuries, even under the strong mitigation to meet temperature targets set by the Paris Agreement.
 
This is an interesting study, by quantifying sea-level rise until 2300 and its sensitivity to the pathway of emissions during this century. The very insightful finding from this study is that it clearly analyses, in a quantitative manner, the benefit of earlier mitigation, i.e., lower median sea level rise and much reduced risk of a low-probability, high-end sea level rise scenario by 2300.

So our near-term action in coming decades will impact the long-term sea level rise, and society needs good guidance from studies such as this for adaptation and mitigation planning for future sea-level rise.

Last updated: 20 Feb 2018 4:18pm
Associate Professor Pete Strutton from the Institute for Marine and Antarctic Studies at the University of Tasmania and the ARC Centre of Excellence for Climate System Science

This is exactly the kind of work that people need to hear about.

We need to realise that climate change is happening. Even if we stop emitting today, the effects of our past emissions will be felt for centuries to come and every year that we delay action has consequences for the future.

Last updated: 20 Feb 2018 4:13pm
Professor Charitha Pattiaratchi is Leader at the Australian National Facility for Ocean Gliders (ANFOG) and is from the Oceans Graduate School & The UWA Oceans Institute, University of Western Australia

This interesting paper examined global mean sea level rise and conclude that the global sea levels will rise between 0.7 and 1.2 metres by 2300 in response to different emission pathways.

However, a similar sea level increase could occur within the next decade due to a combination of nodal tides and the El Nino Southern Oscillation effects irrespective of mean sea level rise due to global warming. The nodal tides are due to changes in the Moon’s orbit that occur every 18.6 years.

Currently we are in the low part of this cycle and in south-west Australia – over the next nine years the sea level will increase by 0.25 m due to this effect alone. This increase in water level due to tidal effect over the next 10 years is higher than that observed over the last century (0.15m).

Similarly, La Nina events increase the mean sea level by up to 0.30 m for a total mean sea level rise of 0.55m.

Last updated: 20 Feb 2018 4:11pm
Professor William Laurance is director of the Centre for Tropical Environmental and Sustainability Sciences (TESS) at James Cook University

This study tells us it’s time to put our money where our mouth is. I think we should encourage all the climate skeptics and big fossil-fuel investors to live smack on the shorefront.

That way, if they’re right about climate change, they’ll be happy as clams. But if they’re wrong, they can just live with the clams, and then let’s see how happy they are.

Last updated: 20 Feb 2018 4:09pm
Ian Lowe is Emeritus professor of science, technology and society at Griffith University, Qld and former President of the Australian Conservation Foundation.

This paper is yet another reminder that climate change is already a serious threat to coastal communities. Sea level rise and storm surges will be a real problem for those living in coastal areas, as well as threatening nearby infrastructure, including several of our airports.

Displacement of island communities in the Pacific will inevitably be a social and political issue for Australia.

These considerations underline the need for an urgent and concerted initiative to decarbonise our energy supply and improve the efficiency of using energy, since the scale of the problems will be directly determined by the effectiveness of our policies to implement the Paris agreement.

At this stage, our national response is totally inadequate.

Last updated: 20 Feb 2018 4:06pm
Associate Professor Grant Wardell-Johnson is from the ARC Centre for Mine Site Restoration and School of Molecular and Life Sciences, as well as President of the Australian Council of Environment Deans and Directors (ACEDD), and from Curtin University

This is just another article building the mountains of information quantifying the necessity for society to act.
 
Yes and it’s another important study clearly articulating the seriousness of delayed action on human-generated climate disruption.
 
This comes out a few days after we learn about the green light given by government to increases in greenhouse emissions from nearly 60 Australian industrial sites. This cancels out the hundreds of millions of dollars spent on emissions cuts under the coalitions Direct Action climate policy.
 
So-called Direct Action by society means we spend some money – but we are keep the status quo. And the status quo means very serious disruption to humanity this century.
 
We all know where this will end. So we are all partying instead of acting.  If it was imminent war threatening our survival – society would be united against the threat – led by leaders with a sense of genuine purpose and vision.
 
But it’s much more serious than war. This article is about sea level rise – but there is now ample evidence and regular updates as the details of the seriousness of humanities situation becomes ever clearer.
 
This is not just an article to scare the people in harbour-side mansions. If a major proportion of the world’s population is displaced, it is a problem for everyone. And there is plenty known about the delayed impacts of current emissions inland. Let alone keeping emissions full steam ahead.
 
But it won’t be us – it will be our children that bear the brunt of our lack of genuine action. Does society really care when we are having so much fun today?

Last updated: 20 Feb 2018 3:33pm
Professor Tim Naish, Director, Antarctic Research Centre, Victoria University of Wellington, New Zealand

The paper by Matthias Mengel and colleagues in Nature Communications this week shows that even with stringent greenhouse gas emissions mitigation as agreed to in the Paris Agreement the planet will still be committed to ongoing rising sea-levels to the year 2300. Their result is not surprising and is in line with recent studies by Golledge and colleagues (2015, Nature) and DeConto and Pollard (2016, Nature), which show that the thermal inertia in the ocean and Antarctic ice sheet results in multi-centennial sea-level rise even if net zero emissions are achieved by the end of the century.  

Of significance, however, is that they show that the mitigation pathway to zero emissions matters and that for every five years' delay in reaching peak carbon, an additional 20cm of sea-level rise occurs. Therefore, global sea-level could be between 0.7 to 1.2m above present by 2300. This paper together with a developing understanding that a stability threshold in Antarctica’s ice sheets might be crossed at 1.5-2C global warming, reinforces the urgency for nations to dramatically increase their nationally determined contribution (pledge) at the first, five-yearly stocktake in 2020.

Emissions must peak as soon as possible, followed by aggressive reduction to zero emissions well before the end of the century, if we are to significantly reduce the risk extreme sea-level rise associated with rapid collapse of the West Antarctic Ice Sheet.

This research is timely especially this week as Victoria University of Wellington hosts the Pacific Climate Change Conference. Pacific Island nations were strong advocates that the Paris Agreement ensure parties make a genuine attempt to restrict global warming to nearer 1.5C above pre-industrial levels, as a number of studies were already showing that sea-level rise in a 2C world could flood some of most vulnerable lowest lying island nations such as Kiribati and Tuvalu.

Last updated: 20 Feb 2018 10:31am
Professor Dave Frame, director, New Zealand Climate Change Research Institute, Victoria University of Wellington, New Zealand

This is a great example of how delays to mitigation can make the costs of climate change add up. It also shows, again, the importance of the thermal expansion and mountain glaciers for sea-level rise this century. 

I don't think arguments about sea-level rise are anything like a game-changer, because if people aren't prepared to mitigate on behalf of their children, whom they love, it's hard to see how information about people 300 years away will do more to alter their behaviour.

Last updated: 20 Feb 2018 10:24am

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