Recently I was involved in a discussion on failed global warming predictions, and the topic turned to rising sea level. Sea levels are indeed rising, as shown by tidal station data, so that’s not a point of disagreement. A discussion of the effects, though, can be surprisingly contentious. One participate made the off-the-cuff remark that in a century Florida would be a collection of islands, with only elevations of 100 feet or more above the seas. The problem is that no, it won’t, and that’s by Anthropomorphic Global Warming supporters’ own projected numbers.
To understand why, all you need is simple arithmetic. For the seas to rise a hundred feet in a hundred years, they would have to rise one foot per year. Since sea level rise is measured in the metric system, let’s convert this to millimeters. 1 foot = 304.8 mm exactly. This is how many millimeters the seas will have to rise every year for a Schlock Mercenary Florida Archipelago to arise in 100 years. Since the most extreme projection in sea level rise is 20 mm a year, that’s not going to happen. 100 feet 100 x 304.8 mm = 30,480 mm (30.48 meters), so it would take 30,480/20 = 1,524 years for the seas to increase by that much. That’s over 15 times longer than the off-the-cuff prediction.
This illustrates the problem with failed global warming predictions: They were based on gut feelings, not hard numbers. Pointing that out is apt to get you labeled “Denier” by the AGW crowd, even when it’s based on running their own numbers. Frankly, if they had done that in the first place, their predictions wouldn’t have come back to bite them.
For instance, sea level rise is almost ten times less that the upper limit of 20 mm annually projected by the US National Research Council. Sea level rise is actually around 2.64 mm annually. At that rate it would take about 11,545 years for the seas to climb 30.48 m. Not as dramatic as saying Florida would be a group of islands in a hundred years, but far more accurate.
Some might take issue with that 2.64 mm annual rise, and they have a point. Measuring sea level height is surprisingly complex, since sea height varies due to the gravitational pull of the moon and sun, as well as the weather and whether the ground is sinking or rising. Even satellite based measurement at the same point is going to vary. Traditionally, sea level height is based on an average of tidal station readings for a certain period. Since tidal stations are also affected by what’s going on with the local geology, annual sea level rise is in a range of 0.8 mm to 3.3 mm.
Of course, the assumption has been that this rate will increase due to warming, which is where the US National Research Council came up with a rate between 5.6 mm to 20 mm per year through the 21st Century. Yet on February 11, 2016, NASA announced that the land has soaked up the extra water, resulting in a decline in sea level rise over the last decade. It’s interesting that this coincides with a lack of warming over the same period, a hiatus of warming that NASA and NOAA deny. It doesn’t help their case that they’ve adjusted historical data, and that three hundred scientists have petitioned the House Science Committee to force NOAA to follow the Data Quality Act.
Let us pause while those screaming “Denier!” get it out of their system.
Okay, now – one more? Done?
To continue, when we get down to the brass tacks, any projection of sea level rise is just that: a projection, and as NASA’s announcement shows sea level rise isn’t well understood. It’s still good to use the upper rate when running numbers because that shows us what would really happen in a worse case scenario. That’s good for deflating sensationalism. To see the actual effects only requires a topographic map, and these are easy to find online. NOAA even has an interactive map that lets you see how much flooding would happen with such-and-such rise in sea level. The NOAA interactive map only goes to 6 feet (1.524 m), so to get an idea about greater heights you have to look at topo and elevation maps.
We should keep in mind there’s a limit to how much melting ice can raise sea levels. According to the American Museum of Natural History, if the ice caps and all the glaciers were to melt, the seas would rise about 70 meters. That’s 230 feet. At 20 mm a year, it would take 3,500 years.
It turns out there’s another limit: How long it would take for all that ice to melt. At least one estimate puts it at about 5,000 years. So, 70 m x 1,1000 = 70,000 mm/ 5,000 = 14 mm a year. That’s less than the US National Research Council top estimate.
To be fair, the US NRC estimate was a range of total rise in sea level by the end of the century. It’s entirely possible that the sea level rise might reach or exceed 20 mm a year, and then drop to a lower rate – just like they’re slowing now (cough). It’s an interesting cross-check, though.
Just think: The first Egyptian pyramids were built over 4,600 years ago. It would potentially take longer than the pyramids have stood in Egypt for the seas to rise to 70m.
That’s the benefit of running numbers. It puts things in perspective.