I should have posted this yesterday but I have been very ill and my brain is a bit fuzzy atm. You should all read this link from NOAA about the short cycle events I was referring to when I posted that graph of the major glaciation cycles. https://www.ncdc.noaa.gov/paleo/abrupt/data3.html
Dansgaard-Oeschger events happen every thousand to three thousand years on average, Heinrich events happen every 10,000 years. When they line up to reinforce each other you can get quite an abrupt shift in whatever the current state of the climate is, sometimes they will cause a long decline to pause or reverse direction for a period, other times they will cause it to drop much faster than the average for a period.
There is a tendency for human being to look for the 'key stone' factor in every pattern we find in nature. Focusing on just the sun, or just CO2, or just Methane... The truth is there are innumerable factors all forcing things in different directions and when a forcing in a direction lines up TaDa Abrupt Change occurs!
The more scientists learn and publish about climate the more of these wiggle and gyrations they find and the elusive keystone factor continues to retreat. What makes putting so much CO2 out there risky is the Earth has three known relatively stable conditions. In the paleo climate record we know the Earth likes to hold an average temperature of 22C at the top end or a frigid 12C at the bottom end. Under strong forcing these numbers can be pushed up or down a couple degrees C but at no time since the origin of life and the development of the carbon cycle have we greatly exceeded these two values. The other thing we know from the record is there is a halfway climate state that is also relatively stable that cycles around 17C.
When the average temperature of the whole earth is 12-10C then major to massive glaciation takes place, at the very coldest nearly the entire ocean surface has ice on it. So much water is in continental glaciers that the entire continental shelf is laid bare and sea level is around 650 feet aka 200 meters.
At 21-23C on the other end of the spectrum the earth is truly a hothouse with semi-tropical conditions prevailing as far as 65 degrees north and south of the equator and temperate conditions extending all the way to the geographic poles. Under these conditions all of the water on the planet is found as liquid or water vapor with the possible exception of high mountains near the poles where snow might persist.
At 17C where the Earth wavered around from 34,000,000 ybp until about 3,000,000 the Earth was divided by hemispheric weather patterns. The Northern Hemisphere was semi-tropical to at least 63 degrees north, we find palm tree pollen and other fossil evidence of that ecosystem in Greenland, the Canadian Arctic Archepelligo, Alaska and Siberia and finally Scandinavia. At the same time the island of Greenland was nearly ice free outside of the mountains and there were Hippopotami wading in the Thames river near the current location of London, England. At the exact same time Antarctica still had a very large ice sheet, but it now appears all the ice shelves around the periphery were melted away and much of what we call the West Antarctic Ice Sheet was also absent which all put world sea levels circa 12-25 meters above today's levels depending on whose estimates you believe are most reliable. Part of the problem is erosion from the ice sheets over the last 3,000,000 years in the north has greatly changed the landscape. It is likely that the Great Lakes and Hudson's Bay in North America did not exist as such, and that the island of great Britain wasn't an island at all, but part of a plain where the mountains of Scotland and Wales were a kind of continental chain loosely connecting up into Scandinavia. The great Ice Sheets pushing out from the higher mountains in Scandinavia and the mountains on Baffin Island scraped away hundreds of feet of material and pushed it south. Its appears from some of the literature that the North Sea was a vast fertile plain before the ice age struck the north. Even more confounding is the isostatic rebound effect, all that two miles of ice on the continents weighed a heck of a lot and land everywhere they stood is still rising. IIRC the world record currently is in the western edge of Hudson's Bay where the land is still rising by about a centimeter a year outpacing sea level rise and actually getting higher above sea level. Another confounding variable is the gravimetric pull of the ice sheets working against the centripetal force of the earths rotation. The gravity field warping effects of the ice sheets pull water towards the poles while the centripetal angular momentum of the rotation pulls the water towards the equator. When more ice is at the poles they exert more gravitational pull and shift more ocean water towards the poles. When there is less the opposite happens and more water accumulates around the equator. As a bonus effect when more water is attracted in either direction it adds too the gravitational effect making it even stronger than a first order approximation.
When we lose the Greenland ice sheet, which I now believe is unavoidable, the sea level in the north Atlantic may actually go down from the gravitational effect dissipating more than the additional volume of water would add. There are scientists who believe absent the ice sheet the coast of Greenland, Labrador, northern Newfoundland, Iceland and Scotland may actually go down as much as a meter. But all that water relaxing away from Greenland is still going somewhere and the where is the equator and a lessor and lessor effect south of the equator.
On the other hand if Antarctica loses the entire Western Ice Shelf that is almost as much water as Greenland, and in that case the magnifying effect will be the equator and lessor and lessor north of the equator.
In this fashion Greenland probably adds enough to Antarctica to keep sea level there relatively stable if Antarctica also loses the WAIS keeping levels stable in the north Atlantic. Either way the people who get the double whammy are the equatorial coastal folks, the Amazon and Congo rivers both enter the Atlantic from very near the equator. That means their river deltas will be swamped and the sea level rise will go much further inland into both the Amazon and Congo basins. In the Indian Ocean the effect will be bad for Zanzibar and the Persian Gulf and the major rivers of India, Pakistan and Bangladesh. Further around the equator Indonesia is literally straddling the equator. Some of the smaller island may disappear completely and coastal populations in some of the most densely packed real estate on the planet, Java Island, will be forced to relocate to higher ground. On into the Pacific the Philippines will be hit hard, they have a lot of mountains inland but the bulk of the population currently lives in the coastal plains. Some of the atoll islands in the mid pacific like Wake and Midway will be swamped out of existence and return to being just coral reefs, and folks in Hawaii and French Polynesia will have to move up higher just like the Indonesians and Philippine citizens.
All in all the Tropics lose and the Northern Hemisphere gains from the exchange of our prior world average 12 C climate for the 17 C climate we are currently on course for. Growing seasons in Scandinavia and the Taiga zone that wrap around the planet between 55 and 70 degrees north will be quadrupled or more in length. Alaska and Sweden already grow world record holding Cabbages because of their extreme daylight periods in summer. Picture that effect with all crops because warmer means they can plant rice and beans and maize as well as the lettuce and cabbage they grow so well now.