Sea-level rise 'could last twice as long as human history'

Research warns of the long timescale of climate change impacts unless urgent action is taken to cut emissions drastically
Damian Carrington The Guardian 8 Feb 16;

Huge sea-level rises caused by climate change will last far longer than the entire history of human civilisation to date, according to new research, unless the brief window of opportunity of the next few decades is used to cut carbon emissions drastically.

Even if global warming is capped at governments’ target of 2C - which is already seen as difficult - 20% of the world’s population will eventually have to migrate away from coasts swamped by rising oceans. Cities including New York, London, Rio de Janeiro, Cairo, Calcutta, Jakarta and Shanghai would all be submerged.

“Much of the carbon we are putting in the air from burning fossil fuels will stay there for thousands of years,” said Prof Peter Clark, at Oregon State University in the US and who led the new work. “People need to understand that the effects of climate change won’t go away, at least not for thousands of generations.”

“The long-term view sends the chilling message of what the real risks and consequences are of the fossil fuel era,” said Prof Thomas Stocker, at the University of Bern, Switzerland and also part of the research team. “It will commit us to massive adaptation efforts so that for many, dislocation and migration becomes the only option.”

The report, published in the journal Nature Climate Change, notes most research looks at the impacts of global warming by 2100 and so misses one of the biggest consequences for civilisation - the long-term melting of polar ice caps and sea-level rise.

This is because the great ice sheets take thousand of years to react fully to higher temperatures. The researchers say this long-term view raises moral questions about the kind of environment being passed down to future generations.

The research shows that even with climate change limited to 2C by tough emissions cuts, sea level would rise by 25 metres over the next 2,000 years or so and remain there for at least 10,000 years - twice as long as human history. If today’s burning of coal, oil and gas is not curbed, the sea would rise by 50m, completely changing the map of the world.

“We can’t keep building seawalls that are 25m high,” said Clark. “Entire populations of cities will eventually have to move.”

By far the greatest contributor to the sea level rise - about 80% - would be the melting of the Antarctic ice sheet. Another new study in Nature Climate Change published on Monday reveals that some large Antarctic ice sheets are dangerously close to losing the sea ice shelves that hold back their flow into the ocean.

Huge floating sea ice shelves around Antarctica provide buttresses for the glaciers and ice sheets on the continent. But when they are lost to melting, as happened the with Larsen B shelf in 2002, the speed of flow into the ocean can increase eightfold.

Johannes Fürst, at the University of Erlangen-Nürnberg in Germany and colleagues, calculated that just 5% of the ice shelf in the Bellingshausen Sea and 7% in the Amundsen Sea can be lost before their buttressing effect vanishes. “This is worrying because it is in these regions that we have observed the highest rates of ice-shelf thinning over the past two decades,” he said.

Avoiding the long-term swamping of many of the world’s greatest cities is already difficult, given the amount carbon dioxide already released into the atmosphere. “Sea-level rise is already baked into the system,” said Prof Stocker, one of the world’s leading climate scientists.

However, the rise could be reduced and delayed if carbon is removed from the atmosphere in the future, he said: “If you are very optimistic and think we will be in the position by 2050 or 2070 to have a global scale carbon removal scheme - which sounds very science fiction - you could pump down CO2 levels. But there is no indication that this is technically possible.” A further difficulty is the large amount of heat and CO2 already stored in the oceans.

Prof Stocker said: “The actions of the next 30 years are absolutely crucial for putting us on a path that avoids the [worst] outcomes and ensuring, at least in the next 200 years, the impacts are limited and give us time to adapt.”

The researchers argue that a new industrial revolution is required to deliver a global energy system that emits no carbon at all. They conclude: “The success of the [UN climate summit in] Paris meeting, and of every future meeting, must be evaluated not only by levels of national commitments, but also by looking at how they will lead ultimately to the point when zero-carbon energy systems become the obvious choice for everyone.”

“We are making choices that will affect our grandchildren’s grandchildren and beyond,” said Prof Daniel Schrag, at Harvard University in the US. “We need to think carefully about the long timescales of what we are unleashing.”

A long, hot view: Climate change likely to extend across next 10,000 years
New long-term scenarios lend new urgency to fast-tracking carbon curbs
BOSTON COLLEGE EurekAlert 8 Feb 16;

Chestnut Hill, Mass (02/08/2016) - The damaging climate consequences of carbon emissions will grow and persist for millennia without a dramatic new global energy strategy, according to a new set of research-based climate change scenarios developed by an international team of scientists.

Rising global temperatures, ice field and glacial melting and rising sea levels are among the climatic changes that could ultimately lead to the submergence of coastal areas that are home to 1.3 billion people today, according to the report, published online today by the journal Nature Climate Change.

The findings, the authors write, hold implications for policy makers because the projections reveal the intractability of a climate change across millennia. This long view, they note, should add urgency to efforts to significantly curb carbon emissions within the next few decades, not gradually across the remainder of the 21st century.

"This long-term view shows that the next few decades offer a brief window of opportunity to minimize large-scale and potentially catastrophic climate change that will extend longer than the entire history of human civilization thus far," the team concluded.

The new projections are based on leading research into contemporary and historical climate data, but also new scientific reconstructions of the only comparable period in human history: the last Ice Age.

"This is the most comprehensive look at global climate in the past, present and future," said Boston College paleo-climatologist Jeremy Shakun, a co-author of the report. "What our analysis shows is that this era of global warming will be as big as the end of the Ice Age. And what we are seeing is a massive departure from the environmental stability civilization has enjoyed during the last 10,000 years of its development."

The international team of co-authors, led by Peter Clark of Oregon State University, generated new scenarios for temperature rise, glacial melting, sea-level rise and coastal flooding based on state-of-the-art climate and ice sheet models.

Under the most conservative scenario, the researchers used a projected global output of 1,280 billion tons of carbon across the next few centuries, far below estimated reserves of at least 9,500 billion tons.

The projected consequences at this level of carbon emissions include:

* Global average temperature increase will exceed the recognized "guardrail" limit of 2 degrees Celsius.
*Melting of glaciers and the massive ice sheets of Greenland and Antarctica will combine for a rise in sea levels of 25 meters, or about 80 feet.
* Coastal submersion could displace as many as 1.3 billion people worldwide, a number that now accounts for approximately 19 percent of the world's population.
* As many as 25 "megacities" around the world could see rising oceans force at least 50 percent of their populations from their homes and businesses.

The consequences of the three other scenarios, which range as high as total carbon emissions of 5,120 billion tons, are substantially greater and should be considered "increasingly likely" given contemporary growth in carbon emissions, according to the report.

The perspective on the future-looking projections comes from looking back at the last Ice Age, which ended approximately 10,000 years ago.

Shakun and other climate scientists have developed a clearer portrait of that era of glacial melting and how the climate responded to and recovered from than era of significant climatic changes.

The team notes scientists have reconstructed a record of natural carbon emission, temperature rise, glacial melting and sea-level rise stretching back 20,000 years to the peak of the Ice Age.

That paleo-climatological portrait shows, for example, that the sea-level rise of 130 meters required roughly 10,000 years to retreat as a stabilized climate emerged in which human civilization has flourished.

"This gives us the opportunity to provide the long view on global temperature and sea level rise, from the end of the Ice Age to today and then onward another 10,000 years into the future," said Shakun. "This sort of side-by-side comparison of the long past and the long future has not been shown before, but is useful for seeing the geological scale to the consequences of carbon emissions since the dawn of industrialization until our actions today."

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