Guardian Scratching for Climate Tipping Points

Raising a block of buildings on Lake Street, Chicago. Public domain image, Edward Mendel – Chicago Historical Society

Guest essay by Eric Worrall

According to The Guardian, the melting of Greenland, which could take centuries, could trigger several meters sea level rise and a cascade of other urgent tipping points. But rising sea level is no threat to the world’s cities. Much of Chicago and Seattle is many feet above the original street level, because people in the 1800s wanted to save their districts from flooding.

The tipping points at the heart of the climate crisis

Michael Marshall

Sun 20 Sep 2020 02.00 AEST

Many parts of the Earth’s climate system have been destabilised by warming, from ice sheets and ocean currents to the Amazon rainforest – and scientists believe that if one collapses others could follow

The warning signs are flashing red. The California wildfires were surely made worse by the impacts of global heating. A study published in July warned that the Arctic is undergoing “an abrupt climate change event” that will probably lead to dramatic changes. As if to underline the point, on 14 September it was reported that a huge ice shelf in northeast Greenland had torn itself apart, worn away by warm waters lapping in from beneath.

Tipping points

We have known for years that many parts of the climate have so-called tipping points. That means a gentle push, like a slow and steady warming, can cause them to change in a big way that is wholly disproportionate to the trigger. If we hit one of these tipping points, we may not have any practical way to stop the unfolding consequences.

The Greenland ice sheet is one example of a tipping point. It contains enough ice to raise global sea levels by seven metres, if it were all to melt. And it is prone to runaway melting.

The collapse would take centuries, which is some comfort, but such collapses are difficult to turn off. Perhaps we could swiftly cool the planet to below the 1.6C threshold, but that would not suffice, as Greenland would be melting uncontrollably. Instead, says Winkelmann, we would have to cool things down much more – it’s not clear by how much. Tipping points that behave like this are sometimes described as “irreversible”, which is confusing; in reality they can be reversed, but it takes a much bigger push than the one that set them off in the first place.

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Is that it? Is a “tipping point” which takes centuries to manifest really the best they can muster?

A Greenland melting event which took centuries is just not a situation most people would recognise as a crisis. A metre per century of sea level rise would just barely be noticeable on human timescales, because people who redevelop houses, buildings or streets at risk of flooding would simply use land fill to raise the level of the land, as they have always done.

Trying to solve the urban planning problems of the distant future makes as little sense as our ancestors in 1894 trying to figure out how cities in the 1940s would deal with the growing urban horse manure crisis.

Even if after many centuries we did end up with a hothouse Earth, the hothouse ages of the distant past were not a world in crisis; much of the land during past hothouses was covered in lush tropical forests.

The only period in relatively recent times when life on Earth may truly have been at risk of a mass extinction was the depths of the last ice age; CO2 levels dropped so low all the world’s plants almost died. Raising CO2 levels to get as far as possible from a repeat of that crisis is a good thing.

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via Watts Up With That?

September 20, 2020 at 12:28AM

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