The Ars Technica article kindly submitted here is based on a World Bank press release that has prompted many news articles today. Several of the articles mention the underlying World Bank report .PDF file "Turn Down the Heat: Why a 4°C Warmer World Must Be Avoided,"

http://climatechange.worldbank.org/sites/default/files/Turn_...

which was a dead link for me the first few times I tried to follow the link, but is working fine as I type this.

The World Bank report was "written by a team from the Potsdam Institute for Climate Impact Research and Climate Analytics, including Hans Joachim Schellnhuber, William Hare, Olivia Serdeczny, Sophie Adams" and other co-authors. Other scientists and commentators reviewed the report, with acknowledgment from the World Bank, and the bank expressed gratitude to the organization Connect4Climate for contributions to the production of the report.

The Ars Technica article summarizes the report as estimating that even if all countries are able to meet their current emissions pledges there's still a 20 percent chance global average temperatures will rise by 4°C by the end of the century. Predicted sea level rise would be a half-meter or more.

Just last week here on HN another participant shared a speculative essay by science fiction author Charlie Stross on the world 500 years from now. Stross predicted sea-level rise of at least a meter, so I looked up sources about the effect of sea level rise. An interesting series of online maps shows projections of flooded land based on various degrees of sea level rise for places of interest such as New York City,

http://geology.com/sea-level-rise/new-york.shtml

San Francisco,

http://geology.com/sea-level-rise/san-francisco.shtml

the Netherlands and England,

http://geology.com/sea-level-rise/netherlands.shtml

and Chesapeake Bay.

http://geology.com/sea-level-rise/washington.shtml

In all cases, the maps default to showing seven meters of sea level rise and do not project any civil engineering projects to protect existing infrastructure. Having read Matt Ridley's blog post "Go Dutch"

http://www.rationaloptimist.com/blog/go-dutch.aspx

back when it was published, I wonder if the most dire predictions about the Netherlands are true, or if the Netherlands, the land of polders,

http://static.nai.nl/polders/e/index.html

can continue to be "living proof to climate pessimists that dwelling below sea level is no problem if you are prosperous."

The report continues with dire predictions of hot summers and changes in rainfall. "It is my hope that this report shocks us into action," is World Bank President Jim Yong Kim's statement about the report. "Even for those of us already committed to fighting climate change, I hope it causes us to work with much more urgency."

I fully agree with the premise that there will continued widespread use of fossil hydrocarbon fuels for electricity generation, transportation, and building heating. There are no effective incentives in place today, nor any likely in the next few decades, to prevent further consumption of fossil hydrocarbons, and that will surely result in a substantial increase in atmospheric concentration in CO2.

Predicting climate change is a safe prediction any time, because over 100 year and especially 500 year time scales, we have often observed climate change in historic times. Over longer time scales, but since Homo sapiens populated much of the earth, rock art in the Sahara Desert shows that the Sahara was once much less arid than it is now, and cave art in Europe shows that the climate of Europe was once much more frigid than it is now.

I live in the United States Midwest, and my mother grew up in a hotter part of the United States Midwest during the Dust Bowl era. Most of her family is still near the family farm on the windswept Great Plains. I don't expect any part of the earth to become uninhabitably hot. We have, according to the best developed models of influences on world climate, a sure prospect of a generally warmer Earth, warming currently lethally cold areas into areas that will be habitable. My experience living in subtropical east Asia in two long stays about two decades apart suggests that we will have more warming of cold areas than turning hot areas into unbearably hot areas from global warming.

Despite the dire predictions in the World Bank report, it is not necessarily the case that port cities will be inundated even by more substantial sea level rise than is anticipated by the report. New York City is sufficiently prosperous to attract some of the world's brightest minds to live there (I know some young people who have moved there recently) and the current city administration actively encourages making New York City a technology hub. New York will thrive, whatever the climate.

http://abcnews.go.com/blogs/technology/2012/11/new-york-can-...

Venice and New Orleans have been in long-term decline for quite a while, from bad governance, and will surely suffer further relative decline, regardless of sea levels. There will still be a great port at the mouth of the Mississippi-Missouri river system, and it will be a thriving and cosmopolitan city, but it may well be in a different place along the river delta from the current location of New Orleans. Venice may basically vanish, but current ports that matter for the world economy will gain the infrastructure investment to build up protection against the sea faster than the sea will rise.

There is much more interesting content in the long World Bank report referenced in the submitted article, but allow me to explain why I think the high end of global warming predictions (and thus the high end of sea level rise and climate pattern change predictions) is unlikely. We already have a known model for induced global cooling from the "natural experiment" of volcanos erupting and ejecting much dust high into the atmosphere. If the climate change we now experience produces more pain than gain (where I live, at 800 feet above sea level in a continental dry, cold winter climate zone, global warming has so far mostly produced gain), then there will be political and economic incentives to sequester greenhouse gases, or directly shade the Earth with high-altitude dust, or to do whatever else science discovers to slow and perhaps eventually reverse global warming. The end of the century is about eighty-eight years from now, and surely our understanding of climate models and geoengineering possibilities will be stronger then than it is now. Over the time span of the report, I would expect enough of an increase in understanding of climate models to bring about workable means to moderate global warming and shape climate change in the direction of making most inhabited regions better off.