The antarctic ice seems already to be melting, so Miami (also the port regions of most cities -- Shanghai has like 15M people living in likely flood zones!) is going under at this stage no matter what we do. Likewise the deep ocean circulation has already begun to collapse, so an anoxic ocean floor seems inevitable. The mass extinction event seems under way already.

But the modelling is noisy, so no one can give you serious answers to "how will this affect people" that will meet your demand for precision. But the worst cases are all disastrous. Things like "we can't grow food in south asia to feed the 2-3 billion people there" are very much on the table.

Miami isn’t going anywhere for at least a few hundred years, by which point they will have plenty of time/tech to keep things above water. The most likely models show 1 to 4.3 feet of rise by 2100 compared to 2000 [0] which has relatively low impact on miami other than the miami beach [1] which is already making plans for keeping/getting flood and rain waters out.

[0]https://www.climate.gov/news-features/understanding-climate/...

[1]https://coast.noaa.gov/slr/#/layer/slr/3/-8927718.607502826/...

Sea level rise will be unevenly distributed, because of gravitational, rebound, and other effects. That tool helpfully provides local scenarios, and the "intermediate high" scenario for Miami Beach corresponds to 6 feet of sea level rise by 2100 [0].

[0] https://coast.noaa.gov/slr/#/layer/sce/2/-9015288.864066828/... (select "view by scenario")

The highest probability model (intermediate) shows 3.7 feet of rise by 2100 which again really only affects the beach area, if you look at intermediate high (lower probability of corresponding to reality) scenario it starts to hit at some of the areas around the miami river, but again this is far cry from miami being definitively underwater and does not account for riverwalls, floodwalls that are being planned and installed.

The different scenarios are not constructed to represent the probability distribution of likely outcomes, and the "intermediate" scenario does not represent the "highest probability model".

Indeed, given that unpredictable human behaviour is the main driver of the response, it is very difficult to construct a "most likely scenario". Instead, what can be said is "given an emissions scenario (or range of scenarios), these are the probabilities of different outcomes". The sea level rise scenarios themselves only describe the outcomes, and do not correspond to the probabilities.

The mapping between emissions scenarios and outcomes can be found in Table 4 here [0]. You may note that for low emissions scenarios the exceedance probabilities don't look too bad, but there is still considerable risk.

[0] https://tidesandcurrents.noaa.gov/publications/techrpt83_Glo...

Sea level rise can be extremely nonlinear. There are glaciers in Antarctica that are like the cork in the wine bottle. If the "gatekeeper glacier" is gone, the sea water gets into the basin that's below sea level and will melt all the multi kilometer thick ice in that basin.

Each can provide meters of sea level rise. You can check out Eric Rignot's presentations from youtube.

We don't know if the melting of such a gatekeeper glacier will take ten, fifty or a hundred years. But it has started.

You can't extrapolate this effect from just looking at recent past temperature and sea level rise - it's a whole different mechanism.

Not to mention, many parts of Miami are already built on artificial land. My uncle's place is in East Fort Lauderdale, which is an artificial network of peninsulas. sort of like this [1] but connected to land. New houses are build higher. Realistically I think accommodating rising sea levels is going to be accommodated incrementally by new development.

1. https://en.m.wikipedia.org/wiki/Palm_Islands#:~:text=The%20P....

I don't think I have that much need for precision. But it would be good to have at least some analysis of the costs of an additional 0.5 degree increase, given that limiting climate change is one of the biggest global efforts right now, and the costs of that effort. And maybe that analysis exists, but if so I haven't seen it. We shouldn't be having these big global efforts without clearly explaining to the public exactly why it is worth the investment over other things we could be investing in to improve global health.

If there is a good chance food production will drop significantly with the additional 0.5 degree, it probably makes sense to invest a lot to meet the goal of 1.5 vs 2.0. If the main concern is flooding and a smaller drop in food production, it might make more sense to invest in more intensive farming (we are certainly nowhere near the ceiling of easy gains here) and better infrastructure.

How much would a sea wall around Miami or Shanghai cost?

A sea wall around Miami wouldn't help due to the karst substrate; water would flow through the limestone channels under any wall. The main concern with sea level rise in South Florida isn't that the seawater will come in but that rainwater won't drain away. There will have to be a huge investment in pumping systems.

That investment is likely cheaper and more feasible than geo-engineering the globe's climate.

> I see some people say it is going to make earth uninhabitable

Not even the worst case scenarios from the IPCC show anything even remotely close to ‘uninhabitable earth’ - the people saying that are being even more disingenuous and pseudoscientific than climate deniers. Some fringe regions of the planet may become a lot harder to live in (note that climate change is not uniform, it will affect some places a lot more than others) and of course some coastal areas may experience more flooding but by and large day to day living in the first world will be similar to what it is today even with 2C of warming.

I have a citation[0] that disagrees with your characterization, suggesting (the obvious) that while it may technically be possible for humans to live in harsh environments, they tend not to, they tend to live in a small subset of all places, and climate change will move those places everywhere, even in the first world.

"We show that for thousands of years, humans have concentrated in a surprisingly narrow subset of Earth’s available climates, characterized by mean annual temperatures around ∼13 °C. This distribution likely reflects a human temperature niche related to fundamental constraints. We demonstrate that depending on scenarios of population growth and warming, over the coming 50 y, 1 to 3 billion people are projected to be left outside the climate conditions that have served humanity well over the past 6,000 y."

Unless you are cheating by saying 'first world' without noting that the places constituting the first world will likely migrate rapidly in the coming century.

[0] https://www.pnas.org/content/117/21/11350

‘humans tend not to live in warmer regions’ is entirely different than, ‘make earth uninhabitable’ — but even in that source it shows the concentration of harsher climates as being in the third world (india, africa, south america).

This seems incorrect. Perth, Western Australia has a mean annual temperature around 18°C, and my understanding is many people find the climate here agreeable. There are warmer cities in this country which also seem to be attractive destinations for migration.

The planet will be stable under our models, but what about the humans? There are mass migration scenarios in the models and mass migration always leads to instability. Our species is capable of unspeakable violence.

Migration due to climate will happen over centuries. It's not like a war where one second it's livable and the next second, shells are flying. It's incredibly slow incremental change.

In a hypothetical world without climate change, billions of people would be moving around the world over the next century or two anyway.

I hope you’re right and I’m sorry for sounding so cynical. I live in a city that invited a climate change denier to keynote our renewable city conference. He wasn’t even a good climate change denier - we found the absolute bottom of the barrel lunatic type. That still kills me and makes me genuinely worry that we’re a little too dumb to make it out of this one with the first world intact.

Edit - I’d honestly rather not articulate my fears for the developing world.

> Humans’ ability to efficiently shed heat has enabled us to range over every continent, but a wet-bulb temperature (TW) of 35°C marks our upper physiological limit, and much lower values have serious health and productivity impacts. Climate models project the first 35°C TW occurrences by the mid-21st century. However, a comprehensive evaluation of weather station data shows that some coastal subtropical locations have already reported a TW of 35°C and that extreme humid heat overall has more than doubled in frequency since 1979.

https://advances.sciencemag.org/content/6/19/eaaw1838.full

> fringe regions

I wouldn't call India a fringe region and typically cities are hardest hit.

I'm just making assumptions here, but if an average increases by 2 degrees, that could mean that the outlier maximum temperature can reach 4-5 degrees. For areas where this temperature is already in the 45-50(Celsius), that's probably uninhabitable (at least for poor people).

This will probably mean that there will be a wave of ecological emigration moving towards the more temperate areas of the globe.

So, it's not an uninhabitable earth unless you are poor and live around the dry tropical/ecuatorial areas. And there are a lot of people there.

> Some fringe regions of the planet may become a lot harder to live in (note that climate change is not uniform, it will affect some places a lot more than others) and of course some coastal areas may experience more flooding but by and large day to day living in the first world will be similar to what it is today even with 2C of warming.

How can this be known at this point? I can certainly imagine changing weather patterns such as monsoon, drought, heat waves, cold snaps, etc not being limited to fringe regions.

Because we are already seeing it and can model for the future. See the first image in this article and note how some areas have experienced no warming while others a lot as compared to 1900.

https://www.climate.gov/news-features/climate-qa/does-global...

But I would not describe the areas experiencing change as “fringe”. Nor do I see a reason to expect the areas not experiencing change to continue not changing.

‘Experiencing change’ != ‘a lot harder to live in’

I didn’t say only fringe areas would change

In addition, while global warming makes some places harder to live, it makes others more habitable.

Parts of India might get uninhabitable in the summer in some of the worse case scenarios. Given the population there and the fact they're a nuclear armed state that's a geopolitical powder keg.

My understanding is that 2 degrees is not that harmful in itself, but it would lead to further uncontrollable runaway increases due to release of methane locked in frozen tundra.

That, and also we would be reflecting less heat from the sun without the ice, as ice reflects back 90% of the sunlight that hits it, so no ice would lead to even more warming.

In a dynamic system anyone who says they know the consequences with a high degree of certitude is blowing smoke.

Oddly the most reasonable course of action is to always paint the worst possible future but it will presumably spur people to greater action. If it turns out to be incorrect there's no harm is there? It's not like we can overreact to climate change.

Unless of course we can.

>If it turns out to be incorrect there's no harm is there? It's not like we can overreact to climate change.

We can. Human life is still resource constrained. While we live better lives than ever before, it's something that can always improve. The resources we spend on dealing with climate change could've been used to improve the lives of people instead. An investment in the economy today can have (positive) compounding effects in the future.

We could live like people lived in the middle ages, but that would cause more human suffering than it would help. The same point goes for the future though - if we stop technological advancement, then how many people will suffer from issues of the modern day that would be solved in the future?

Ultimately, it's a balancing act on what will help more people more in the long run.

Of course we can, ban fossil fuels overnight and nuke everyone who doesn't comply, nuclear winters are good against global warming. Reducing carbon emissions is tame as far as possible responses go, there are some extreme solutions involving geoengineering.

It won't happen because there are more incentives for underreacting than overreacting but yes, definitely possible.

The harm in being incorrect is that more and more people will use the past incorrect statements as grounds to dismiss future potentially correct statements.

My ballpark guess: climate regions will shift north by a few hundred miles. In some places that will mean tundra turns to forest, in other places farmland will turn to desert. Sea levels will also rise by a few feet.

But then there will be a couple billion people living in the wrong place; they will have to move across national borders in huge numbers. This is historically linked to political instability and sometimes war.

The worst part will be what we do to each other as a result of climate change, rather than the change itself, imho.

This is an interesting paper in this regard:

Bastin et al, Understanding climate change from a global analysis of city analogues:

https://journals.plos.org/plosone/article?id=10.1371/journal...

"Even under an optimistic climate scenario (RCP 4.5), we found that 77% of future cities are very likely to experience a climate that is closer to that of another existing city than to its own current climate. In addition, 22% of cities will experience climate conditions that are not currently experienced by any existing major cities. "

"We notably predict that Madrid’s climate in 2050 will resemble Marrakech’s climate today, Stockholm will resemble Budapest, London to Barcelona, Moscow to Sofia, Seattle to San Francisco, Tokyo to Changsha."

The information might not be new, but the way it is presented is quite tangible, since many people have an understanding of today's conditions in different cities.

From what I recall, RCP 4.5 is closer to "status quo" than "optimistic" at least for a while yet.

I agree. The authors probably had a bad day.

Conferences can be depressing. The IPCC reports contain the very basic rock-solid consensus of what can be expected, but while playing around with data and models things can look much scarier.

Well, I guess I better buy property in Seattle, then.

> What are the actual consequences of the globe warming by 2 degrees instead of 1.5 degrees?

IPCC SR1.5 [0] deals with this question. Figure SPM.2 [1] is probably a good place to start for a quick look, and the summary for policymakers has 4 pages (part B) that all seem directly related to your question.

[0] https://www.ipcc.ch/sr15/

[1] https://www.ipcc.ch/sr15/chapter/spm/b/spm2/

My main worry is increasing droughts that will jeopardize our food supply.

Prepare now... pressure your state to build reservoirs.

The problem with food reservoirs is that the stuff at the bottom tends to go bad before you can get to it.

Reservoirs as in lakes for water.

Climate change has been shown in many studies to increase food production, because carbon is an input to photosynthesis.

We can't predict shit like whether is gonna be sunny tomorrow, truth is the consequences of climate change are unknown, as the earth is a terribly complex system.

Just like Covid, economics, politics... my only prediction is that most predictions will sound stupid after we start feeling the effects of climate change (for good or bad reasons, who knows).

My personal philosophy is not to mess with complex systems if that can have fatal consequences, but I guess we are way past this point.