Ratty, that is just waffle, not proof of "the simple fact that there has been nett positive gain from global warming". Your list of gains would indeed be positive, unless they were offset by factors such as an increase in the range of pests, changes in rainfall, increases in max temperatures that kill crops, loss of land to drought or flooding etc. Nature is much more complicated than whatever you think you know about "finance". There is no proof of a "nett positive gain from global warming".

Raff,
The statement There is no proof of a "nett positive gain from global warming". is a bit off the mark.
Go back to first principles, if we get cooling down to the temperatures of 50k years ago then we have a net loss for humans, if we have a cooling to LIA conditions then there's a net loss for humans. Historically the evidence is that warmer conditions than now were beneficial to the Minoans, Romans and their contemporaries. So evidence suggests at least another 2'C from current to Minoan Climate Optimum conditions will give a net gain.

Sandy, that is just speculation, not evidence relevant to the present-day. You don't even know the global temperature at the time of the Minoans, Romans or anyone else comparable. Only some vague estimates with wide error margins from proxies whose veracity you would at other times question. So saying there would be a certain gain from a global rise of 2C above a temperature you don't know is not sensible (being polite). And that is without considering the different circumstances (ecological, population etc) the now exist.

Ratty, your position has changed from the insupportable "the simple fact that there has been nett positive gain from global warming" to "The simple fact is that more food is being produced on less land than at any other time in history." The latter is doubtless true. The former is a groundless assertion that you don't even try to defend but instead you slide effortlessly into a defense of fossil fuels.

Raff,

that is just speculation, not evidence relevant to the present-day

What evidence is there that it is not relevant? We have more advanced technology, particularly in agriculture which is most relevant in this discussion. Isn't the whole of this discussion based on speculation, yours that we're all doomed by 2'C rise from current, mine that it will be beneficial At least I have physical evidence rather than models to base my arguments on.

As it happens I think proxies have their place in looking at the past, like models you have to be careful how you use them. There is plenty of of evidence, as has been pointed out already, that there have been warmer period than now in the current interglacial. Here's another piece of evidence

Sandy, you don't have "physical evidence". None at all. Your ancient comparisons are irrelevant for at least these reasons and doubtless more:

- you have no way of knowing whether the temperature was optimal. Perhaps they would have been more successful still with global temperatures 2C lower.

- the circumstances are different. There were relatively small populations (compared to today's) living in an environment that was almost certainly under less ecological pressure.

- you are extrapolating from a region to the whole world with no obvious reason to think our whole world of 7 billion resembles the ancient Mediterranean.

You also introduce a favorite straw-man of "we're all doomed by 2'C rise", which I have never seen anyone apart from "skeptics" say.

The paper on melting Peruvian glaciers is indeed interesting, indicating that Peru was at similar temperatures then as now.

Ratty, more food being produced on less ground than ever before is in itself obviously a net gain. But considering the immense changes to agriculture over the last 50 years, the improved productivity has nothing obvious to do with proving any "nett positive gain from global warming".

So just as nobody can provide evidence of research organizations lying, neither can anybody provide any proof of net gains from warming. Yet these two items seem to be articles of faith among "skeptics". As I said before, this seems to be evidence of brainwashing.

Raff
So are you saying that we'll be OK with a 2'C rise in GAT?
So are you saying that computer models are better than proxies at guessing the future?
So are you saying that despite having technology and developing new technologies all the time we're still going to have severe problems due to population even if we fix GAT?

Breath of Fresh Air
You're a fine one to talk ;-)

Ratty, no you suggested only that gains in agriculture are due to temperature and not to technological change, which is pretty stupid. Disentangle the one from the other (what part is temp change and what part is technology) and you might have an argument, but there is no way to do that.

Sandy, so you have sensibly dropped ancient Rome as "physical evidence" that warming will be beneficial. What other physical evidence do you have in its place? And whether "we" will be OK, I very much doubt the consequences of warming will be evenly distributed, do you?

Raff,
I haven't dropped anything, I'm trying to find out what you actually believe to be the best method of working out the potential benefits of an increase in GAT of 2.0'C.

As far as I can tell from your evasive answers you haven't got a clue and have a vague idea that models based on selective proxies are bang on the money.

Of course changes in climate affect the globe differently in different places, where I grew up in Scotland was once under a mile of ice, at the same time where I currently live in France had a population of Neanderthal surviving reasonably well. Given the choice between at bit more warming and "reversing climate change" back 50K years the population of Northern Europe, Asia and America should be hoping for another Minoan Climate Optimum. BTW I'd like some evidence that the previous warm periods weren't in fact warmer than today.

http://www.tourismelimousin.com/en/Triptyque-homepage2/Landing/Family-fun-in-Limousin/Neanderthal-Man-Museum-in-Correze

Raff
Perhaps you should pop over to WUWT and correct all the misconceptions here (Climate and Human Civilization over the last 18,000 years) straight?

Sandy, I don't know the best method of estimating gains and losses from CC and neither do I know whether previous warm periods were warmer or cooler than now, nor whether they were "optimal" in any one region. What I am quite sure of is that saying that a contemporary 2C rise will be beneficial because some ancient civilization did very nicely at some unknown global temperature is a non sequitur.

Ratty, you claim that "the rise so far has been beneficial" and yet have no evidence for that. Sandy says "evidence suggests at least another 2'C from current to Minoan Climate Optimum conditions will give a net gain" and yet cannot identify that evidence. Your belief system seems to be evidence free.

Raff

I don't know the best method of estimating gains and losses from CC and neither do I know whether previous warm periods were warmer or cooler than now, nor whether they were "optimal" in any one region.

How can you have a discussion with someone who doesn't know and doesn't accept the lessons of history, it's like arguing with a Parrot who continually says I'm a clever boy you idiot

Sandy you provide no "lessons of history". You have no facts to help you. You don't know what global temperatures were with any accuracy in historic Crete or Rome. You don't know whether these temperatures were at, above or below "optimal" conditions. And you don't know whether adding 2C to today's (or pre-industrial, not sure what you mean) temperatures would land us at, above or below ancient conditions. Yet you believe this unknown outcome would be a positive change. It is a logical proposition only a fool would support.

Raff
all I can do is suggest you read the following
The Little Ice Age: How Climate Made History 1300-1850 by Brian M. Fagan
A History of the Vandals by Torsten Cumberland Jacobsen
The Illustrated Encyclopedia of the Aztec and Maya by Charles Philips
Sea Peoples of the Bronze Age Mediterranean c.1400 BC1000 BC by Raffaele DAmato
http://scrippsscholars.ucsd.edu/gsugihara/content/climate-change-and-demise-minoan-civilization
http://academic.emporia.edu/aberjame/student/fitch1/abrupt_e.html#climate

Other things to check are the rise and fall of the rise and fall of empires due to climate. I know that you hate Micheal Mann's use of tree rings but you could google this Tree rings suggest Roman world was warmer than thought

You then have to compare what you've read with your extensive knowledge of climate and climate models and decide whether, in general, a warmer climate is more beneficial than a cooler one.

Sandy, the Minoan paper is interesting. It puzzles me that despite knowing so much about how changes in climate can cause great civilizations to fail, you are committed to the idea that, to borrow a quote, "this time is different" - that current climate change will be beneficial.

Depends in which direction the climate changes, generally warmer good cooler bad for want of a better expression.

Anasazi began raising maize and other crops. They also produced skillfully woven baskets. By a.d. 700, the Anasazi were building pueblos, or villages, along with extraordinary pottery marked by elaborate black-on-white designs. Their villages, built at the top of mesas or in hollowed-out natural caves at the base of canyons, included multiple-room dwellings and complex apartment structures of stone or adobe masonry. Despite their successful culture, the Anasazi way of life declined in the 1300s, probably because of drought and intertribal warfare.

LIA 1300-1870