21 replies to this topic

[jethro]

The Medieval Warm Period, The Little Ice Age and the settlement and exodus from Greenland by the Vikings crop up in numerous threads. The discussions tend to get lost so here's a dedicated place to discuss them at length. Feel free to include any historical time period.

[jethro]

I haven't seen this before, nor have I read any more than the opening page but it looks interesting:

http://www.intechope...-little-ice-age

[ElectricSnowStorm]

good idea J, I really want to know what caused warming periods long before the car, the world has been warmer, what goes into the atmosphere now and what went into it then?? its interesting to know if the same gases went up as today but from different sources, then what caused the iceage? warming then cooling climate patterns must be the sun, the only most powerful source to do that..but with other effects from the ground greatly influencing this..

Edited by nimbilus, 04 November 2010 - 03:00 .

[ElectricSnowStorm]

..without the sun theirs wouldn't be any warmth heat at all, so lower the suns effects and it would be cooler? of course, but not that simple as it affects the upper atmosphere which effects the troposphere that creates the weather, sea temps affect the weather and climate, cloud cover from sea temp and land temps, all by the sunshine. during ancient times were the more volcanic eruptions at once more frequent, more forest fires?? how much arctic ice, how much rainforest, than modern times? (please move post(s) if not right for the thread) (:

Edited by nimbilus, 04 November 2010 - 02:55 .

[scottish skier]

nimbilus, on 04 November 2010 - 02:53 , said:

..without the sun theirs wouldn't be any warmth heat at all, so lower the suns effects and it would be cooler?

Interesting you should ask that. I asked the better half what the atmosphere did for earth just last night to see what a non-weather/science freak thinks. I asked did the atm...

(1) keep the earth's surface warmer than it would be without it?
(2) keep the earth's surface cooler than it would be without it?

She looked at me funny and answered 'the first of course - that's the greenhouse effect!'.However, they are both actually correct as written with respect to a person standing on earth. The atmopshere does not specifically keep us warm, nor cold, at least not locally, it stablises temperature. Without it, the surface of the earth would be more like the moon - hot enough (above +100 C) to boil water in the middle of the day, below -100 C at night. The correct way to think about it is what the atmosphere specifically does is to buffer these extremes to a large extent, depending on where you are, giving a global average temperature which is generally higher (estimate is often 33 C, but still debated) than what it would be without it.

If you want to see the extremes, you need to go where there is little water; surface, vegaetative, not atmospheric - e.g. the sahara desert. Then you can see what a less water-buffered (the main greenhouse gas with the highest heat capacity) atmosphere feels like; +45 C in the day dropping to freezing at night. Bit more like the surface of the moon...

Cheers,

SS

[ElectricSnowStorm]

Interesting SS. another part of a post (above) i mentioned about heat produced from the earths surface, with no sun no light from up their and no moon light as it reflects the sun. im going make a thread on this.
right this is about (think im going off topic) climate history, so what caused the medieval warm period?
the evidence from ice cores, tree rings, and i think insects? shows warming and cooling periods.

[Weather Ship]

A brief extract from, Climate, History and the Modern World, by H.H. Lamb, Routledge.

More is known now than when this book was first published about the exchanges that go on between the Arctic seas and the climate over wider areas and longer times (which we return to on p. 271). The great increase of ice on the East Greenland Sea in the mid-I960s, and the low salinity water that accompanied it, migrated from there slowly to affect the western Atlantic in the years that followed and, after a long clockwise circuit over the western ocean, was carried back into the Iceland region after fourteen more years. In the meantime there had been a rather warmer, more saline phase near Iceland. A study by Dickson and others in 19881 followed the progress of the anomaly and the cycle of changes that went with it over nearly two decades. And this inspired others, notably Mysak and his co-workers at the Centre for Climate and Global Change Research and the Department of Meteorology at McGill University, Montreal, to trace the anomaly back through its earlier history before it first reached the Greenland Sea. Its origin is found to have been in a greatly boosted. runoff into the Arctic Ocean north of Canada from the North Amencan rivers, mainly the Mackenzie River system in the western part of northern Canad.a, in the early 1960s.

The paper by Mysak, Manack and Marsden , Sea –Ice Anomalies Observed in the Greenland and Labrador Seas during 1901-1984 and their relation to an interdecadal Arctic climate cycle.

http://www.geog.mcgi...no.-1989-14.pdf

Edited by weather ship, 12 November 2010 - 17:30 .

[scottish skier]

weather ship, on 12 November 2010 - 17:29 , said:

A brief extract from, Climate, History and the Modern World, by H.H. Lamb, Routledge.

Very interesting read. I had not heard/thought about this factor before; i.e. the contribution from surface run-off of fresh water into the arctic from the surrounding continents... This water should of course float outwards over the denser saline sea water, potentially increasing the freezing temperature of the surface water from -2.3 C back towards zero. Without signficant currents/redistribtuion and turnover (vertical mixing) it would make perfect sense that this could cause very signficant increases in sea ice, at least locally. Increased temperatures cause increased rainfall over certain regions causing increased fresh runoff into the arctic causing an increase in ice cover and increased cooling before the cycle turns on itself and reverses. Such work shows the common belief that ice in Arctic has been constant until AGW came along as complete rubbish.

This paper is from a while back (20+ years is a long time in science). Whether it is a good example, I'm not sure as I don't know how much such work is incorportated into current theories but.... Often in science, the same things are studied twice or more. Someone notices something and reports it in a paper. However, at that point in time it is not 'hot' science, so it goes rather unoticed. Then, 10, 20 years later the topic is hot and someone studies the same thing again, unaware that there is already a study on it, publishing findings without considering earlier studies. I had a classic example of this a few years ago. Nature paper announces that hydrogen can form clathrate hydrates - hydrates could be a new clean H2 storage material! Authors very pleased with themselves until, someone says - actually, this was discovered 20 years ago but nobody cared too much about it then, so it went in standard journal to gather dust.... All you have done is rediscovered it.

I wonder how much early, pre-AGW work on ice, glaciers etc goes 'unoticed'. Old stuff is often better than modern science too - scientists of the past were often much more methodical as they were less driven to get the latest out asap.. things went at a slower pace.

Edited by scottish skier, 12 November 2010 - 19:45 .

[stewfox]

jethro, on 03 November 2010 - 23:39 , said:

I haven't seen this before, nor have I read any more than the opening page but it looks interesting:

http://www.intechope...-little-ice-age

Interesting read , people can always jump to page 20 for the summary.

Suggest at least a Nothern Hempishere pattern of changes rather then just for example the MWP just effecting a few areas (e.g NW Europe).

[Weather Ship]

The attached figure illustrates (roughly) how the boundary between water of Gulf Stream origin and the polar water at the surface of the North Atlantic Ocean has varied. The biggest temperature changes are found near the furthest advances of the cold water or ice replacing a previously warmer surface (or vice versa). Thus a large area between the Bay of Biscay and mid-Atlantic was 10-12 °C colder at the climax of the last ice age around twenty thousand years ago than in our own times. An area between Iceland and the Faeroe Islands (61deg. N) seems to have been 5 °C colder than the modern average between about AD 1675 and 1705.

Interestingly the southward limit polar water east of Iceland has sometimes been approached over short periods of up to a few weeks in recent years. For example , in April 1968 and again in 1969 this water-mass advanced to near the Faeroe Islands, and more briefly a number of times in the first half of 1979.

Positions of the boundary in the ocean surface between water of Gulf Stream origin and the polar ocean current from near northeast Greenland in the twentieth-century warmest years and at various times past.

Excuse the drawing=I'm no Picasso!

Yellow- Warm Period 20^th century.

A.D 1675-1700

7-8000BC

8300BC

White-65-70,000 years ago.
Ice Age climax, 17,000-20,000 years ago.

Edited by weather ship, 14 November 2010 - 15:38 .

[stewfox]

weather ship, on 14 November 2010 - 15:33 , said:

Positions of the boundary in the ocean surface between water of Gulf Stream origin and the polar ocean current from near northeast Greenland in the twentieth-century warmest years and at various times past.

Excuse the drawing=I'm no Picasso!

Yellow- Warm Period 20^th century.

A.D 1675-1700

7-8000BC

8300BC

White-65-70,000 years ago.
Ice Age climax, 17,000-20,000 years ago.

Interesting , where did you get the data from, any link ?

I assume the 'gulf stream' still played its part but was switch off re last ice age 17000 yrs ago ?

[Weather Ship]

No link that I know of. The source was Hubert Lamb's Climate, History and the Modern World. (2nd edition). As you know Lamb was one of the leading climatologists of the last cemtury.

Water of 'Gulf Stream' origin still played its part in the sense it was the boundary between the cold water down as far as Biscay and the warmer water, somewhat different to today, but it has to be remembered that atmospheric circulation was vastly different. So it wasn't so much a swithch off but a completely different ball game.

[NorthNorfolkWeather]

weather ship, on 17 November 2010 - 06:54 , said:

No link that I know of. The source was Hubert Lamb's Climate, History and the Modern World. (2nd edition). As you know Lamb was one of the leading climatologists of the last cemtury.

Water of 'Gulf Stream' origin still played its part in the sense it was the boundary between the cold water down as far as Biscay and the warmer water, somewhat different to today, but it has to be remembered that atmospheric circulation was vastly different. So it wasn't so much a swithch off but a completely different ball game.

Hubert Lamb was indeed one of the leading Climatologists and was at the UEA School of Climate Studies before they went over to the "Warm side". It was Professor Lamb who first pointed, with any academic authority, out that we were in an interglacial, that could end sooner rather than later

[Summer of 95]

It's a fascinating subject, but I can't help thinking that research on it has focused too much on Europe. There are IMO events in other parts of the world that need looking at regarding climate changes in the last 2000 years, such as:

*The Polynesian expansion that coincided with Europe's "Medieval Warm period"; Scandinavians settling Greenland was impressive, but people from tropical islands sailing to southern New Zealand and settling there (they even reached the Auckland Islands below 50S) was phenomenal. And was the cooling asociated with the LIA behind the population collapse on Easter Island? Looking at the climate data, that island is currently right on the tropical/subtropical border line; 2-3C warmer (AD1000?) and they'd have no trouble growing stuff from Tahiti. 2-3C cooler (AD1600?) and most of their tropical crops would fail, except perhaps the sweet potato which still grows there now.

*All the central Asian tribes that suddenly appeared on the borders of Europe in the 1200s. Hell-bent on world domination, or sensing a cold period was starting in their homelands and looking for somewhere more amenable? (Some of them had done the same thing at the start of the cold period around 4-500 as well).

*The rise of civilisations in the Americas that also coincided with the Medieval Warm Period

[paul tall]

scottish skier, on 05 November 2010 - 17:46 , said:

Interesting you should ask that. I asked the better half what the atmosphere did for earth just last night to see what a non-weather/science freak thinks. I asked did the atm...

(1) keep the earth's surface warmer than it would be without it?
(2) keep the earth's surface cooler than it would be without it?

She looked at me funny and answered 'the first of course - that's the greenhouse effect!'.However, they are both actually correct as written with respect to a person standing on earth. The atmopshere does not specifically keep us warm, nor cold, at least not locally, it stablises temperature. Without it, the surface of the earth would be more like the moon - hot enough (above +100 C) to boil water in the middle of the day, below -100 C at night. The correct way to think about it is what the atmosphere specifically does is to buffer these extremes to a large extent, depending on where you are, giving a global average temperature which is generally higher (estimate is often 33 C, but still debated) than what it would be without it.

If you want to see the extremes, you need to go where there is little water; surface, vegaetative, not atmospheric - e.g. the sahara desert. Then you can see what a less water-buffered (the main greenhouse gas with the highest heat capacity) atmosphere feels like; +45 C in the day dropping to freezing at night. Bit more like the surface of the moon...

Cheers,

SS

Where exactly in the Sahara is it 45+ by day and freezing at night. Or any desert in fact.

If there is one common misconception that gets my goat it is the "boiling by day, freezing by night in the desert" comments.

There is no site on earth that commonly gets 45 degrees in the afternoon and 0 at night. If such a site exists show it to me.

Go to Las Vegas, or Phoenix, or Luxor, in the summer when it is 40-45º by day, or Baghdad or Death Valley where it is more like 45-50 and tell me what the night time temperatures are on those days? A frost doesn't enter the equation.

These fabled 45/0 desert locations do not exist.

Anyway, sorry about picking one sentence, back to the topics at hand...

Edited by paul tall, 05 December 2010 - 13:02 .

[Gray-Wolf]

I just thought dry air (as opposed to saturated air) was naff at holding onto 'heat'?

[paul tall]

Perhaps it is, but no site on earth suffers such daily extremes.

Yes we've all heard very rare stories of temperatures in winter/spring rising from -20 to +10 in a matter of hours due to warm fronts and fohn winds etc - but that is really the opposite of 45 degree afternoon heat in the summer under established stagnant hot air (nowhere that I am aware of gets 45 degrees in winter) somehow turning into an air frost. It just doesn't happen.

And meteorological records from 10s of thousands of places back this up.

[Weather Ship]

I think in fact you are both right, The Snake River Plain in the US has a diurnal variation that goes from around 100 deg. F to the low 40s. Whereas Washington D. C. will only have a variation of 15 deg F because it's much more humid. Water Vapour absorbs radiation within certain wavelengths and is an important ingredient in the 'greenhouse' equation.

[paul tall]

Can I have a link to the weather records of any station in that area that has an average max/min of 38/6 in summer, and I'll shut up.

Thanks

[paul tall]

Boise max/min for July, 32/14. Granted the low is relatively cool compared to the high and some days will have a greater/lesser diurnal range, but that average is nothing like 45/0.

Pocatello max/min for July 30/10. That's quite extreme to be fair. But again, it's not in the same league as the boiling/freezing type desert climates that I've heard of but never seen any evidence of.

Also looking at the map, it appears that the Snake River Plain is in a giant valley surrounded by very high mountains, so I'd guess an excellent natural frost hollow, as cold air would readily sink down to the plain - this is in fact evidenced in the climatic averages, as places that average 32º in the summer you'd expect night temperatures to be approaching 20º, not 10º.

But with all the geological advantages it's temperatures come nowhere near the sort of diurnal ranges that people claim for deserts.