Global sea levels rose faster in the 20th century than at any time in the past 3,000 years – And, Surprise, It’s Your Fault

By Paul Homewood

http://www.dailymail.co.uk/sciencetech/article-3458468/Global-sea-levels-rose-faster-20th-century-time-past-3-000-years-climate-change-blame.html

The Mail is referring to the new paper, Temperature-driven global sea-level variability in the Common Era, by Robert Kopp et al.

ABSTRACT

We assess the relationship between temperature and global sea-level (GSL) variability over the Common Era through a statistical metaanalysis of proxy relative sea-level reconstructions and tide-gauge data. GSL rose at 0.1 ± 0.1 mm/y (2σ) over 0–700 CE. A GSL fall of 0.2 ± 0.2 mm/y over 1000–1400 CE is associated with ∼0.2 °C global mean cooling. A significant GSL acceleration began in the 19th century and yielded a 20th century rise that is extremely likely (probability P≥0.95) faster than during any of the previous 27 centuries. A semiempirical model calibrated against the GSL reconstruction indicates that, in the absence of anthropogenic climate change, it is extremely likely (P=0.95) that 20th century GSL would have risen by less than 51% of the observed 13.8±1.5 cm. The new semiempirical model largely reconciles previous differences between semiempirical 21st century GSL projections and the process model-based projections summarized in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.

A bit of mumbo jumbo maybe, but this is how they describe the significance:

This is the latest in the line of “everything is hotter/ wetter/drier/stormier etc etc than ever before”.

When these sort of studies are properly examined by the likes of Steve McIntyre, they quickly lose all credibility. Unfortunately we need an army of Steves to keep up. Hopefully however, he will have time to look at this one.

I do have some observations though, in no particular order:

1) As we know, Greenland ice cores, and other supporting data, show that not only was the MWP warmer than currently, but the rise in temperatures at that time was significantly greater and more rapid than in the last century and a half.

The same applies to earlier warming episodes.

There is no logical reason why sea levels should not have risen at least as fast then.

https://notalotofpeopleknowthat.wordpress.com/2016/02/22/how-the-arctic-climate-has-changed-since-the-mwp/

2) HH Lamb’s Climate, History & The Modern World also shows very rapid changes of upper tree lines in the European Alps around 1000 years ago, both up and back down again, indicating rapid warming there as well.

3) HH Lamb also provides strong evidence that sea levels were at least as high, and probably higher, back in the Middle Ages, and also around 400 AD. In between, sea levels fell, so we know that sea levels have never been the sort of constant thing often portrayed.

For instance, he talks of sea levels dropping by 2 meters between 2000 and 500 BC, a rate of 1.33mm/year. As I think it is safe to assume that this was not a steady rate throughout, it seems reasonable to assume that for much of this period the fall was much greater.

4) The Abstract says this about the period 1000 to 1400 AD:

A GSL fall of 0.2 ± 0.2 mm/y over 1000–1400 CE is associated with ∼0.2 °C global mean cooling.

In other words, 80mm or 3 inches over 400 years.

But why choose that period? We know that the MWP was still going strong certainly well into the 13thC. But, significantly, Lamb also states:

Sea level was again rather lower in the 7th and 8th centuries, but seems to have been again high in the late 13th to 15th centuries.

In other words, there tends to be lag when glaciers keep melting and sea levels keep rising, even though the peak warmth has gone.

Quite simply, why have not the authors shown the sea level fall during the time when it was certainly at its greatest, between the late 16thC and the mid 19thC? I suspect if they did that, we would simply see that it more than offset all of the rise since.

5) And this brings us to the crux. It is undisputed that there was a massive and rapid expansion of glaciers worldwide during the Little Ice Age. (See my list here, for example)

In the European Alps, this began around 1550, and continued in fits and starts till about 1850. Similarly, glaciers in Greenland and Iceland did not reach maximum till the late 19thC.

Exactly the same patterns are seen in South America, Alaska and New Zealand.

There can be no doubt that sea levels fell during this era by far more than the 80mm quoted for the earlier period.

The only question is whether the sea rise in the last century and a half has simply cancelled that out. The evidence suggests otherwise, but even if it has, so what, We are simply back where we were before. The rapid recovery from the Little Ice Age is no more than a reflection of the rapid descent in the first place.