I wrote many replies to different people during open thread 261, as part of it I read up on many of the relevant papers and relevant IPCC reports and discovered lots interesting things, one thing of interest here would be the Special Report on Climate Change and Land, which from what I can tell didn't mention Zhang and Cai (It mentioned a paper by Zhang from 2011 but that's a different paper), It did however mention Zabel and Ramankutty and took it for granted they were true and didn't mention a better estimate.

"The gradual and planetary changes that can cause land degradation/improvement have been studied by global integrated models and Earth observation technologies. Studies of global land suitability for agriculture suggest that climate change will increase the area suitable for agriculture by 2100 in the Northern high latitudes by 16% (Ramankutty et al. 2002) or 5.6 million km2 (Zabel et al. 2014), while tropical regions will experience a loss (Ramankutty et al. 2002; Zabel et al. 2014). "

As I said at the time "despite the fact both papers found massive net positives (world wide) the IPCC still found a way to phrase it in such a way as to leave open the the possibility that the papers suggest the net effect is negative that is they fail to explicitly mention the fact that the losses in the cited papers with respects to tropical regions were found to be much smaller than the gains to northern regions. (I should also add if you were to read it in context it sounds much worse). They then proceed to explain all the various mechanisms responsible for a loss of land with virtually no mention of the various mechanisms by which land would increase." There is a lot more interesting things in the comments to that thread and I go much more into detail.

Something you might also find interesting is the joint research centre world atlas of desertification (which is mentioned in the special report), similar to the IPCC they seem to go out of their way to emphasize the negative effects without outright lying, which sometimes leads to funny graphs and statements where they say something like "Between 1999 and 2013, approximately 20.4% of the Earth’s vegetated land surface showed persistent declining trends in land productivity" which raises the obvious question of what happened to the other 80 percent, there are lots of examples of this and its also important to note that "changes of above-ground biomass and is conceptually different from, and not necessarily related to, agricultural production or income per unit area" but its nevertheless a fun read.

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“I came across a figure of a hundred feet of shift for every foot of sea level rise in a book discussing the situation on the U.S”

I said before this sounds remarkably flat. And it can only be true at high tide, and spring tide at that. The difference between spring and normal high tide is often greater than a foot. It’s a metre where I live - yes that’s mixing imperial and metric but about 3 feet.

Anyway even a road that skirts a beach is a few feet above the beach proper, and houses abetting the beach aren’t at sea level either but a few feet above it.

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"The amount of land lost equals the length of coastline times the amount by which it shifts in."

Not necessarily, if you are computing the amount it shifts just from current elevations. Quite a bit of coastal land is in the form of river deltas, which are quite flat, and would appear to be lost by this criterion. But since silt from the river is deposited in the delta region, land that would apparently be lost may just come back (or never really go away) from this silt deposition.

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OK, thanks. I misunderstood: I thought you were saying that no effects of increased wealth had been taken into account. If only the negative effects have been taken into account and you're trying to rebalance things, fair enough. Any change to the status quo is likely to have positive and negative aspects to it, except in extreme cases.

A change that wiped out humanity, for example, would have no positive aspect for humans that I can think of, although it might be viewed quite positively by some surviving terrestrial creatures, or by visitors from other solar systems.

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I appreciate your thoughtful approach to these questions, and weighing both pros and cons. I had some questions you may have thought about, but I don't believe I've seen your take on them.

Do you think there's a concern about where (almost entirely Canada and Russia) this new usable land might be found? Obviously right now Russia gaining at the expense of other parts of the world isn't exactly politically useful. Both Canada and the parts of Russia who would gain the most, also have the least number of people. I didn't try to do the math, but there may very well be significantly more people actually living in that 24,000 km2 than the 10 million km2 of newly livable lands. People can express interests, while empty tundra cannot. This is certainly not insurmountable, but it does present a variety of political issues. Even the interests that do exist in say, Canada, care about preserving nature and older ways of living, which would also be negatively affected even while the areas become far more hospitable to just about everything else we would want to do there.

Are there good estimates on how much, if any, of the world might become desert? Do people currently live there? That seems like a much better proxy for problematic heat than anything else. Again with the Sahara, like the tundra, habitable land where nobody lives is only a long term benefit, if at all. Significant parts of India turning into desert would be quite a problem, even if it's over 80 years.

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In terms of land becoming useable in the Eastern hemisphere, raw temperature is unlikely to be as significant as permafrost; this is a big reason Siberia and the Russian Far East aren't already a second Europe (another is mountains). My understanding is that while permafrost-melting is a plausible consequence of global temperature rising, this in itself would release a lot of CO2 so it'd be necessary to account for a temperature rise of that magnitude necessarily causing a larger temperature rise.

In North America this isn't much of a problem, but as I understand it population density there is more limited by the Canadian shield (there's something similar in Siberia as well) and a shortage of Canadians to justify bringing the prairies into denser habitation.

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You know the Mark Twain quote about suppositions, in Life on the Mississippi: such a trifle of fact

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So, some land will go but more land will come. This is encouraging. The obvious problem I see is that the land that goes will include people's homes and jobs, and it may not be feasible for them to migrate en masse to the newly available land, probably far away and belonging to a different country.

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