Saturday, March 7, 2009

Sea-levels and Permafrost burials

The calamities that are predicted by those arguing for the need for carbon dioxide emission controls typically focus on the rapid rise in sea levels that are predicted as the temperature continues to rise. The rise in temperature is also anticipated to get more rapid, since, as the tundra that covers much of the countryside along the Arctic Circle warms, it is expected to emit more methane. There are a number of other commentators who are talking about this (and which I will refer to in Saturday Pick Points later today) but I thought I’d dwell just a little more on the Medieval Warming Period Experience to counter the latter. But first a comment on the “rising tides” that are cited as the greatest concern. (They were after all the basis for the court decision that the EPA had to regulate carbon dioxide.)
On April 2, 2007 the Supreme Court released its ruling in the case of the state of Massachusetts vs. the Environmental Protection Agency. Massachusetts and eleven other states, along with several local governments and non-governmental organizations (petitioners), sued the EPA for not regulating the emissions of four greenhouse gases, including carbon dioxide (CO2), from the transportation sector. The petitioners claimed that human-influenced global climate change was causing adverse effects, such as sea-level rise, to the state of Massachusetts. In a 5-4 decision, the court ruled in favor of Massachusetts et al, finding that EPA has the authority to regulate CO2 and other greenhouse gases.

If one goes to the National Institute of Oceanography, in India, one gets this curve for the last sea-level at Mumbai for the past 135 years, and it suggests that there is nothing particularly remarkable about the current changes in sea level, nor is there any discernable effect due to GHG Global Warming.


Sea-level variability at Mumbai, which has the only more-than-century-long sea-level record in the Indian Ocean. Annual sea level (cm) is plotted as a function of time to reveal the variability of the annual sea level over the length of the data record (1878 to 1988 in this figure) (red), showing the inter-annual variability in sea level at Mumbai. Filtering annual sea level with a 10-year boxcar filter (10-year running mean) (blue) reveals inter-decadal variations. At Mumbai, these inter-decadal variations are as large as are the variations from year to year.

The University of Colorado at Boulder has a site that lists, from Tide Gauge Records, the rise in the oceans over the decades, and the site includes this table:

Source University of Colorado Boulder.
With today’s technology it is now possible to see these changes in a more global sense. JPL, for example, has an animation site of seal-levels (the sea-level viewer) which is worth a visit. as well as the patterns shown by major currents.

However if one looks at the satellite measurement of sea levels, one gets:
Source Univ Colorado Boulder

What is interesting is to note that this data comes from two different satellites, and that if one separates the two (Jason and Topex) one gets a slope for the TOPEX of 3.22 mm/yr, but for the Jason data the slope is only 2.4 mm per year, which is more in line with the tide gauge data, but which also suggests that the sea-level rise is slowing down, rather than speeding up. (The average for the two together, I compute to 3.28 mm, but that is rounding).

Now the second point required that I adopt a new bit of technology. The book that I have started to quote more and more from in regard to glaciers, ice sheets etc is Jean Grove’s Little Ice Age of which I have written before. However, as I also noted, the original costs $320, and if you want the new edition it is $850 on Amazon. Much as I find this fascinating, this is a bit steep, and so I borrowed the books from the library. But they had to go back – and hence the step to new technology. I discovered that the book costs $11 on Kindle. Egad! I pay for the machine with one purchase.

I’m still learning how to use the machine, and so it will take a couple of days before I can pull quotes and pictures properly from it to insert here. But here is the relevant section, copied out, that I wanted to point to today. We know from the recent excavations at Sandet in Greenland, that the ground is now permafrost to the surface. However, to quote a little from Grove
It is known that Herjolfsnes remained inhabited until after 1480, though it is clear that the climate had deteriorated by 1350. This is shown by the fact that costumes from burials were penetrated by tree roots until those of the 1350’s and subsequent decades, which remained in remarkable state of preservation, indicating that not long after burials of this time the ground a meter or two deep had become frozen throughout the year (Norlund 1924, Howgard 1925, Gad 1970).

So all the current permafrost in that latitude was not frozen prior to 1350. Thus it was giving off the decomposition products prior to freezing. The farm at Sandet still smells like a midden when its soil is thawed. Ergo if there was no vast global melt-down at the time, and history would surely have recorded one, when these latitudes were not frozen, then there won't be this time. And the Medieval Warming period ran from about 930 to 1350, so I would suggest that we relax and stop all the hysteria.


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5 comments:

  1. Mumbai is perhaps not the best example to use for sea level rise, even in the Indian Ocean. The Proudman Oceangraphic Laboratory show that the continuous annual record stops in 1988. Another problem is that the vertical motion of the observational station at Mumbai is unknown. Vertical motion is caused by tectonic adjustment and the rebound of the earth’s crust following the last glaciation, a process that is still going on.

    In the absence of direct measurement, correction for the latter is often done with a model.
    ”Mean-sea-level data from coastal tide gauges in the north Indian Ocean were used to show that low-frequency variability is consistent among the stations in the basin. Statistically significant trends obtained from records longer than 40 years yielded sea-level-rise estimates between 1.06–1.75 mm yr− 1, with a regional average of 1.29 mm yr− 1, when corrected for global isostatic adjustment (GIA) using model data. These estimates are consistent with the 1–2 mm yr− 1 global sea-level-rise estimates reported by the Intergovernmental Panel on Climate Change. Source

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  2. While I don't have personal knowledge, the quote under the figure is from the Indian Institute and I would have thought they would know. I would agree that you have to recognize the problems of land motion (see for example Bangladesh, or the Mississippi Delta.) and there have certainly been significant ground motion in Europe over time with the changing loads as the glaciers left. (I have a plot somewhere that one day I should turn into a post).

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  3. It's not really valid to interpret sea level rise from tide gauges without considering vertical motion. For example, the land mass on Vancouver Island, where I live, is rising at up to 4 mm per year from the effects of the last glaciation. It's also twisting due to the effects of tectonic motion, which is lifting the southwest corner of the island as much as another 4 mm per year. The tide guage data from Tofino, on the southwest coast of Vancouver Island, show that the water level fell an average 1.7 mm per year over the last 50 years. Despite this, not many people would think the Northwest Pacific is shrinking.

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  4. Actually the first time I used the graph, the whole point of the post was just that very thing, that the land in Bangladesh is sinking more than the sea level is rising, and as a result the sea level increment appears to be under 2 mm.

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