4.5m – 6m of sea level rise is (small) possibility this century – leading climate scientist

In a previous blog, I took the optimistic path on climate change, citing projections that a massive disruption in energy and transport will help us keep global warming below catastrophic levels.  But there are much more dire warnings than even the most recent IPCC report suggests.  One of the leading climate scientists of our time is warning of the horrifying possibility of 4.5 m – 6 m  of sea-level rise within 70 years.

Bad as the January 5 event in Thames and Kaiaua was, imagine the damage and destruction if that storm surge had been 4.5m – 6m higher. And if instead of receding, that wall of water never went away. That is what we could be facing in the not-so-distant future if we don’t dramatically cut fossil-fuel pollution.

Moanataiari sea wall Thames
Moanataiari Thames


Jeff Goodell from Rolling Stone describes the possibility here

“ If that sounds alarmist, watch this short video. In it, you’ll see a scientist named Richard Alley in a Skype discussion. Alley is talking frankly about something that few scientists have the courage to say in public:

As bad as you think climate change might be in the coming decades, reality could be far worse. Within 70 years  Alley says, there’s some risk — small but not as small as you might hope — that the seas could rise as much as 4.5m – 6m.

 4.5 – 6m means not just higher storm surges, but the permanent drowning of virtually every major coastal city in the world.— (Large chunks of Christchurch, Wellington, Dunedin, Napier, Nelson  all gone.)  And I don’t mean “sunny day flooding,” where you get your feet wet on the way to the mall. I mean these cities, and many more, become scuba diving sites.

Richard Alley is not a fringe character in the world of climate change. In fact, he is widely viewed as one of the greatest climate scientists of our time. If there is anyone who understands the full complexity of the risks we face from climate change, it’s Alley. And far from being alarmist, Alley is known for his careful, rigorous science.

For a scientist of Alley’s stature to say that he can’t rule out 4.5m – 6m of sea-level rise in the coming decades is mind-blowing. And it is one of the clearest statements I’ve ever heard of just how much trouble we are in on our rapidly warming planet

To judge how radical this is, compare Alley’s numbers to the latest report from the Intergovernmental Panel on Climate Change, which was released last week.. The report projected that with 2 Celsius of warming, the range of sea level rise we might see by the end of the century is between about 0.3m to 0.3m to 0.9m.

So why is Alley arguing that the risk of catastrophic sea-level rise is so much higher than the IPCC?

 IPCC reports are notoriously conservative. They are written in collaboration with a large group of scientists and are often watered down by endless debate and consensus-building.  They rely on published science that is often out of date — or at least, far from the cutting edge.

Alley simply has a broader understanding of ice dynamics than many scientists, who tend to be highly specialized in their research. Alley’s analysis includes not only geology and paleoclimatology, but also a big dose of physics and engineering — which is especially helpful when it comes to understanding the possibility of rapid ice sheet collapse. In the IPCC report, “tipping points” in the climate system, such as ice-cliff collapse, are either disregarded or buried deep in the 1,000-page document.

For Alley, the engine of potential catastrophe is West Antarctica. If West Antarctica goes, that’s 3m of sea-level rise right there. Then if you add in ice loss from Greenland, a little from East Antarctica and other sources, you quickly get to 4.5m – 6m.

The big question is, how soon could it happen?

 “The most-likely future as projected by the IPCC is well on the small-change/small-damage ‘good’ end of the possible futures, with potential for slightly better, slightly worse, and much worse, but without a balancing ‘much better,’” Alley writes.

In other words, when it comes to ice-sheet collapse, uncertainty is not our friend. The collapse might not happen fast. Then again, he can’t rule out the possibility that it will happen fast, very fast.

Alley points out that the best way to avoid this uncertainty is to keep climate warming below 1.5 Celsius or less. In existing climate models, West Antarctica remains fairly stable below that threshold. But given the world’s current burn rate of fossil fuels, and the massive industrial and political transformation required to keep temperatures below that threshold, Alley knows that’s unlikely.”