Sea Levels Could Rise An Extra 60cm If Emission Reductions Are Delayed Until 2035, Study Finds

ABC Science - Nick Kilvert

Scientists say sea levels will continue to rise until at least 2300. (Getty Images: Brook Mitchell)

Key points: Sea levels are projected to rise between 0.7 and 1.2m above 2000 levels by 2300 Delaying peak emissions between 2020-2035 results in 20cm rise for each 5-year period missed A 2C temperature increase this century could result in a sea-level rise of at least 1.5m

Global sea levels will continue to rise until at least 2300 regardless of how much we reduce our greenhouse gas emissions, according to new research published today.
But for every five years until 2035 that we delay reaching net-zero carbon emissions, as committed to under the Paris agreement targets, sea levels will rise by about an extra 20 centimetres, the researchers found as part of the study published in Nature Communications.
They estimated average global sea levels would be between 0.7 and 1.2 metres above 2000 levels by 2300, depending on how quickly we can reduce our emissions.
The Paris agreement, to which Australia is a signatory, has a core aim of limiting global temperature rise this century to "well below" 2 degrees C above pre-industrial levels, and to pursue efforts to keep the rise below 1.5 degrees.
However, the authors argue that a 2C-temperature increase would result in a sea-level rise of at least 1.5 metres.
"Even if we only look at 2020 to 2035, we can say we need to start greenhouse reduction as soon as possible to reduce the damage," study co-author Alexander Nauels from the University of Melbourne said.

"We will have to adapt to sea-level rise, but it's really a question of how much and how bad it will be."

Time to 'put our money where our mouth is'
The researchers created a computer climate model using the major drivers of sea-level rise — thermal expansion of the ocean, melting of mountain glaciers, and the melting of the Greenland and Antarctic ice sheets.

Scientists say uncertainty about Antarctic melting means sea levels could be higher than projected (Supplied: NASA)

They then plugged in a range of different parameters based on different possible scenarios of emissions-reduction rates, and emissions-peak years under the Paris agreement, and ran each scenario 600 times up until the year 2300.
Their results showed that every delay in peaking emissions by five years between 2020 and 2035, created a 20-centimetre increase in sea levels by 2300.
"Under the Paris agreement, current mitigation commitments by nations to 2030 are at the upper level of the emissions scenarios considered [in the study]," Professor John Church from the Climate Change Centre at UNSW, who was not involved in the study, said in a statement.
"Mitigation efforts will need to be increased significantly and urgently if a rise of more than 1 metre by 2300 is to be avoided."
The most extreme end of the study's results showed a possible sea-level rise of more than 4 metres by 2300. However, the average and median results fell well below that figure.
A Sea-level rise of two metres would mean Sydney's Circular Quay and Botanic Gardens, Brisbane Airport, Melbourne's Docklands, Elizabeth Quay in Perth, and significant areas of the Gold Coast and Darwin would be underwater, according to modelling done last year.
The uncertainty in projections comes from the limited knowledge regarding how positive feedbacks will affect the rate and extent of melting in the Antarctic.
Positive feedbacks occur where one effect amplifies the process that causes it, such as melting ice exposing darker ground, which absorbs more heat resulting in more melting ice.
Modelling for positive feedbacks becomes difficult and means that extreme scenarios cannot be dismissed.
"Even a sea-level rise of up to 3 metres until 2300 cannot be ruled out completely," study author Matthias Mengel said.

"We are not yet fully certain how the Antarctic ice sheet will respond to global warming."

A number of climate scientists have commented on the study, reiterating the importance of immediate and strong action to curb global greenhouse-gas emissions.
"This study tells us it's time to put our money where our mouth is. I think we should encourage all the climate sceptics and big fossil-fuel investors to live smack on the shorefront," Professor Bill Laurance, director of tropical and sustainability science at James Cook University, said.
"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, then let's see how happy they are."

Links

• What can we expect from Australian climate politics in 2017?
• Forget Paris: Australia needs to stop pretending we're tackling climate change
• 'My islands are sinking': Climate activist to feature at Womadelaide
• Forget Paris: Australia needs to stop pretending we're tackling climate change
• Satellites tell us how fast sea levels are rising — and how high they will go
• The challenges of understanding impact of climate change in Antarctica