[LINK] Re: Link Digest, Vol 173, Issue 16

[Stewart Fist]

Danny suggests that my problem is ignorance not scepticism.  I've kept a
database on climate claims for more than twenty years.

Danny counters with the blog authority:

> For the Medieval Warm Period, see
> http://www.realclimate.org/index.php?p=33

which claims

> Medieval Warm Period ("MWP")
>
> Period of relative warmth in some regions of the Northern Hemisphere in
> comparison with the subsequent several centuries. Also referred to as the
> Medieval Warm Epoch (MWE). As with the 'Little Ice Age'(LIA) no well-defined
> precise date range exists. The dates A.D. 900­1300 cover most ranges generally
> used in the literature.

This is aligned with other claims that I have:

>  890-1170 Medieval Warming Period

(ie beginning at the end of the Viking period, and finishing at time of the
Crusades)

-----------------------


However, I spent a lot of time a few years ago trying to establish these
dates, and the best consensus I got at that time was:

> The climate record reveals that Europe experienced a prolonged warm period
> known as the Medieval Warm Period (MWP) between 600 and 1150, then  cooling of
> the climate between the years 1150 and 1460, followed by a brief warming
> between the years 1460 and 1560, followed by dramatic cooling known as the
> Little Ice Age (LIA) between the years 1560 and 1850.

Other authorities put the beginning of the North Atlantic warming period
(not called the Medieval Warming Period) at around 400 AD and finishing in
the 900-1000 AD period.

Another says about Iceland (c 1200 to 1210)
> Lamb (1995) attributes much of the decline in population to the colder climate
> and increased ice flow The harvest years were so cold that there was little
> hay to feed the livestock so thousands of sheep died. During the MWP
> Icelanders grew grain over much of the island but by the early 1200's only
> barley a short-season grain was being grown.


And for the Bubonic plague decade (1350 to 1359)
> 1352 Population of Europe now 50 million - one-in-three died
> and the harvests failed from the extremely cold

It warmed for a few years, and then went cold again.

> 1420-1440 Cold-turn for few years

One US authority classifies the whole 450 years (1420‹1890 period) as the
Little Ice Age.

But in Europe
> 1434 was said to be warmest summer on record before 1964

Then
> 1500-1600 was loosely called "Little" Medieval Warm Period. Temperatures, on
average, were higher than average 20th C.

However other source puts Little Ice Age beginning in 1580
> 1550 to 1850: Main part of Little Ice Age: Global temperatures at coldest
> since beginning of Holocene.  Mean average temperatures about 1.0 degrees C
> lower than today.  In the grips of the Little Ice Age, the glaciers are
> lengthening, fisheries slowly collapsed, famine became common (leading to
> increased international conflict - and class conflict as people move to the
> cities - See 1700). The snow load slowly increased at the poles, and the
> salinity of the oceans increased.  This Little Ice Age began slowly and
> progressively, and finished quickly (1860-70)

And another says 
> 1580-1596 Eastern North America, Europe, Scandinavia and the Middle
> East - an intense warm phase of unmatched strength.

So the 20 year period between 1580 and 1600 is claimed both by the Little
Ice Age daters as freezing, and the Little Medieval Warmers as a warm period
of 'unmatched strength'.  And this is a period with good historical records.

Then ten years later:

> 1600-1700 Known as coldest period of the Little Ice Age

but contrast this with

>1700 on, showing a decided improvement in climate.

then
>  The winter of 1709 killed many people in France Conditions were so bad a
priest in Angers in west-central France wrote: "The cold began on January 6,
1709, and lasted in all its rigor until the twenty-fourth. The crops that
had been sewn were all completely destroyed... Most of the hens had died of
cold as had the beasts in the stables When any poultry did survive the cold
their combs were seen to freeze and fall off. Many birds, ducks, partridges,
woodcock, and blackbirds, died and were found on the roads and on the thick
ice and frequent snow Oaks ashes and other valley trees split with cold Two
thirds of the vines died... No grape harvest was gathered at all in Anjou...
I myself did not get enough wine from my vineyard to fill a nutshell."

Asia was also changeable and unpredictable, even for the natives.

In 1750:
> Ahmad Shah's army, retreating from Persia, is said to have lost 18,000 men
> near what is present-day Herat, Afghanistan from cold in a single night.

---------------------

Frankly, just a comparison of these different claims to authority show just
how dicey all this scientific certainty is ... and how little attention has
been paid to building a basis of factual evidence upon which to base
predictions.

Gulf Stream changes can account for European cooling, but its hard to see
how it can account for warming.


My point is that you can't have foresight without having hindsight.

-- 
Stewart Fist, writer, journalist, film-maker
70 Middle Harbour Road, LINDFIELD, 2070, NSW, Australia
Ph +61 (2) 9416 7458