John’s Blog/Newsletter: SEA LEVEL RISE NOW

How Long For The Ice to Melt?

It’s surprisingly difficult to predict the time for ice to melt. You can try a simple demonstration. Take a few ice cubes and put them on your desk or table. If you need to protect furniture you can put them on a dish, but the melting water adds to the intrigue…

First, note the obvious: Nothing will stop the melting, short of putting the ice into a freezer. The warmer it is, the faster the melting.

But the key point to grasp is that there is no way to predict precisely when the last bit of ice will have turned into water.

Very likely, the cubes will not all disappear at the same time. There are lots of variables: Factors such as the room temperature and the heat from your body, if you get close enough. Moving your hand, might change the air currents bringing warmer air to the ice. Even two apparently identical ice cubes may have slightly different mass and will almost certainly have different crystalline structure and stress cracks. All of those things will affect the rate of melting. The bigger the piece of ice, the more the variables and the unpredictability.

As a bigger example of the difficulty to predict the precise melt rate of ice, I was told this story by an MIT graduate engineer. Their class was given a very large block of ice, several feet across. The students were each asked to calculate exactly when it would be fully melted. Most quickly estimated that it would take more than one day.

To get the precise hours and minutes, they tried to take into account the ice volume and all the thermal characteristics in the room, with sophisticated calculations. Yet the students reached widely different answers. No one accurately predicted the time when the last piece in fact disappeared.

The lesson was the subtlety and complexity of the factors that would actually determine the outcome. This was difficult even for a class of very smart engineers, studying thermal dynamics where they could fully observe and measure the chunk of ice in a rather stable environment.

Antarctica and Greenland are REALLY big blocks of ice in extremely unstable environments. Estimating their precise melt rate over the next 50 – 100 years is vastly more difficult than the MIT science lab example.

Combined they are about twice the size of the United States. The ice averages two miles high – ten thousand feet; three kilometers. Those two frozen huge masses contain 98% of potential sea level rise, which is 212 feet (65 m). Accurately gauging the rate of melting for those two “ice cubes” is simply not possible, due to the unknowns, starting with how warm the planet will get.

Even if we could know Earth’s future temperature, a range of variables including weather patterns, extreme polar winds, ponding water on the surface, geothermal activity deep underground, glaciers bending around hills and valleys, etc. will all affect the rate of melting.

According to the most recent estimates by experts, we could see the melting of 2-4% of the ice on land this century. That would yield somewhere between four to eight feet of higher global average sea level; a couple of meters, more or less. In the last decade or two, the estimates have kept changing upward and probably will continue to do so as we get updates on how warm the planet is, and how the glaciers are actually melting and collapsing.

I know that it’s really hard to wrap our minds around sea level rising for decades on end. In all recorded human history it has not been higher than now. We have no cultural memory from 122,000 years ago, when it was twenty five feet higher; seven meters. The geologic record is quite clear.

The implications of sea level being much higher are so disturbing that most people simply do not want to contemplate them for more than a few seconds. We really, really like the shoreline just where it is–where it has been for the 5,000 years or so of our civilization. So we shift our focus to something else. Psychologists call this cognitive dissonance.

The ‘something else’ to which we shift our attention may be the related question of how to slow the warming by slowing the increase of carbon dioxide. That’s very important, but that cannot soon stop rising sea level. We have warmed the oceans measurably and that heat will do its work, melting ice for centuries. (As I have pointed out previously we are adding about 500,000 “atomic bombs” of extra heat energy to the ocean every day.)

It is our choice, whether we can begin planning for the future when sea level is higher. The sooner we begin, the easier will be the adaptation. The next building or infrastructure project can be designed so that it allows for the sea to rise, or not.

The choice is “ours.” The ice will melt regardless…

By John Englander July 15, 2019 Sea Level Rise

2 Comments

Ned Baldwin

- 6 years ago Reply

There you go again… statistics with no back up!
98% of potential sea level rise is attributable to melting land ice…..
2 to 4% of ice melted would yield 4 to 8′ of global average SLR…..
I suspect both these statements are “work backs” from other data
and are likely very inaccurate. Previously I have read that seawater heating
alone accounted for nearly 20% of potential; rise.
I am of the opinion that new higher storm surges from new more intense storms are a far bigger problem than long term SLR.
Our coastal infrastructure is so inadequate in many areas that it needs
addressing even if one ignores SLR….

John

- 6 years ago Reply

Ned – In the spirit of openness, I have published your comment and will answer it here — even though you persist in arrogantly assuming I don’t have my facts right, when you should train those questions on yourself. So here we go, one more time — and the last time I am going to give you a platform to be rude and take my time with things you could easily research yourself:
The approximate 98% of ice on land being in those two places, with a total potential SLR of 212 feet comes from this peer reviewed paper: Antarctic Science 21(5), 413–426 (2009) & Antarctic Science Ltd 2009 doi:10.1017/S0954102009990137 “Review – Ice sheet mass balance and sea level” I. ALLISON1*, R.B. ALLEY2, H.A. FRICKER3, R.H. THOMAS4 and R.C. WARNER1
There have been other calculations since, but nothing substantially different. Also, if you want to persist in challenging me, read my book, HIGH TIDE ON MAIN STREET. That reference is literally Reference #1, attached to the very first sentence in the book. From that same reference, I give the breakdown of where the ice is, on page 56.
As for your second point, that thermal expansion of seawater is 20% of the SLR, you are incorrect and draw the wrong inference. This is explained on page 51-52 of my book, but I will explain it here briefly. Over the last century it is well accepted that the oceans are about one degree Celsius warmer (1.8 Fahrenheit). Like most substances, water expands slightly when heated. [Edit revision 20 July] With the oceans averaging about 12,000 feet in depth, their height has increased by about 3 inches in that time. That is roughly one third the total rise in SL over the last century, with the balance coming from the melting of glaciers and ice sheets. But now the rate of melting is increasing exponentially. We are now looking at several feet of SLR this century according to various papers, but the NOAA Report is fine: https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf So, the percentage contribution from thermal expansion varies widely depending on the other component, the contribution from the ice sheets/glaciers. For example, if the world warms 3 more degrees C (5.4 F) this century, thermal expansion of seawater may be as much as a foot, estimated at three times the amount for the previous degree. But if the world is 3 degrees warmer, we could have ten feet of SLR from the ice melting, in which case the part from thermal expansion will have dropped to 10% or so. The point is that percentages do not stay the same as the components change with different drivers. Of course all of my numbers are estimates, purely for the purpose of explaining concepts.
For you and other readers, I hope this is helpful. That is the purpose of my blog posts, which are free and without ads. But this is the last time I am going to entertain you, by doing the research you could do elsewhere. I find your attitude disrespectful. In the future I will not publish any comments by you that are rude. I also am not going to spend a good part of an hour answering your future questions, when I have already made the case in my blog posts or in my book, or they can be found on numerous other good resources. http://www.skepticalscience.com is an excellent one, that is robust and well staffed BTW.
I wish you well in your search for the facts.