Sea level rise expert and consultant John Englander has written a fascinating article on how sea level rise is accelerating at an exponential rate.  He points out how the exponential function is little understood by most people.  As a result, sea level rise will continue to accelerate at a rate which will take almost everyone by surprise.

Englander uses the latest altimetry satellite data which shows that global mean sea level rise in the last five or six years has been 4.5 – 5 mm a year on average.

To illustrate his point about exponential growth Englander asked his readers to guess how long it would take to fill a stadium like Eden Park with water.  (The answer to this question is at the end of this post – see if you can guess)

Imagine if you start with one drop of water in Eden Park and double it every minute. So that means 2 drops in two minutes; 4 drops in three minutes, 8 in four minutes, etc. How long would it take to fill the stadium? 

“The time period for the doubling is the key.  Sea level rise is happening faster and faster, largely due to the melting of glaciers on land, particularly in Greenland and in Antarctica, and thermal expansion of the ocean. A few decades ago, the doubling time for SLR was more than forty years. Two years ago, the doubling time was less than twenty years.  Now the time period for doubling from 2012-18 is already down to 12 years. That acceleration and pattern represents exponential growth and is a problem that we have great difficulty to recognize.”

“As noted on the graph in just 25 years, we can see the rate go from an annual average of 1.5 mm, to 3.2mm, and then  5mm in the most recent short period of six years. While some might argue that we need to wait several decades to confirm the exponential growth, the physics are quite clear and make a case to start planning now.”

“Let’s follow the hypothetical case of it doubling every decade. With the continued doubling, in ten years the current 5 mm, would be a 10 mm a year, then 20, then 40, 80, then 160 mm, per year.”

To be clear, Englander is not saying that we will have 1.6 m of sea level rise a decade this century.

Englander points out that there is no way to know precisely the future acceleration rate of SLR, because of the uncertainty of how quickly the ice sheets will melt, which in large part depends on how warm the planet gets in the next half-century.

“As smart as we humans may be, we have trouble with two concepts that are relevant here: One is to take seriously the concept that sea level can be 3 meters above present, which will move most shorelines kilometres inland. The second is the challenge of exponential growth illustrated above by the time to theoretically fill a stadium with water.

“Because of the phenomenon of exponential growth, sea level is going to rise at a rate that will surprise everyone. The next 50 years will not be anything like the last 50.  It is time to adapt and prepare for the future.”

[Answer to question – Eden Park will be filled to the very top with water in approximately 47 minutes.  Depending on the stadium size it could be one minute more or less.]

This site is the best place to check out the latest sea level rise altimetry over various timeframes and to show regional variations.  This map shows that the waters around New Zealand are rising at a higher rate than many regions of the world – in a band around 4.5mm- 5mm a year