Sea levels rising is only one of the concerns. I think the biggest concern is the reduction of ariable land due to climate change. I.e. the carrying capacity of the Earth will decrease (and I’m of the opinion that the human species has already greatly overshot Earth’s carrying capacity; hence the current degradation of our environment).

I think the species will survive, but may experience a population crash (i.e. mass death), and severly reduced quality of life. I think having 1 or 2 kids is fine for now, and hope I’m wrong in my Malthusian-like thinking.

There is a lot more to it than rise of sea levels on the one hand and some places being too hot.

TL;DR: Climate change causes mass extinctions, ecosystem collapse, extreme weather, and life-threatening heat. Technology alone won’t save us; prevention is crucial. Ignoring climate action risks severe economic damage, comparable to a permanent Great Depression.

(Prepare for a great wall of fuck.)

In short (list is not exhaustive, there’s surely more which I also don’t know of or don’t think of right now):

• Mass extinction of several species, which can’t keep up with the pace of climate change. You might have heard already how insect popluations dramatically declined in the past decades.
• Extinction or even significant deaths and lack of offspring in various species leads to imbalance and collapse of entire eco systems.
• Humans are part of and relying on functioning and healthy eco systems. Without them our very basis of life starts collapsing, leading to numerous human deaths and a lot of misery.
• The occurence of extreme weather conditions as well as catastophes in consequence of climate change increases. The occasional summer storm might become less occasional, which is less of a problem. But so do floodings, hurricanes, tornadoes, droughts or forest fires increase. And those cost lives and do a lot of damage. We experience weather conditions in places today, which most common people would’ve deemed impossible or extremely unlikely at least. (Not every extreme weather condition is the result of climate change though. But a lot are. An entire field of attribution science has emerged to elaborate which catastrophe has been a direct cause of climate change.)
• Increased temperatures, but especially heatwaves, are already now costing more and more lives and that’s not just some particular places with extremely hot temperatures, but it’s also occuring in entire nations known for more temperate conditions. For example in the EU.
• Being “too hot” is only one side. You can survive 40°C or higher, if the air humidity is low. But due to global warming we can also observe time frames in regions where the air humidity plus temperature reaches such levels that people are exposed to life-threatening health risks already at 31°C. (See also “wet bulb temperature” in general.) Higher humidity makes it harder to cool ourselves by sweating, i.e., evaporative cooling. This is being observed more and more often in south-east asia and the middle east but also started to affect the USA in some regions (Texas, last year in 2023).

You might now understand a bit better why even a few degrees more around the globe incur existential threats.

Human beings are remarkably creative when they need to be. […] if the need arose […] some smart ones […] plan it all, and the rest […] build it

(Sorry for quoting you a bit more freely here.)
Technology can do much, but it is not magic. (I’m an engineering scientist, because I realised at some point that I can’t become a magician.) Entropy is a bitch and current solutions or attempts I know of regarding carbon capture are a nice idea at best, but in practise currently not feasibe and therefore a money-pit at worst. “Building higher and cooler” seems a naive approach given the scale and complexity of human lives and disregards the problems we’re facing due to climate change. I don’t mean that condescendingly, rather to highlight how massively impractical that approach would be on the one hand and no solution for most problems caused by climate change on the other hand.
I absolutely think that it’s necessary to continue research in that area, but until we have developed solutions which can tackle the problems we’ve caused in a significant way (which can still take decades until we’ve got large-scale applicable solutions), I think it’s best to practise prevention. Avoid contributing factors to climate change at allmost all costs.
Don’t put all your money on the “technology will save us”-horse.

By the way:
The people who think that climate and environmental protection are damaging the economy are short-sighted, as climate change is projected to cause a tremendous amount financial damage world-wide in the long-term. One of many many sources on this puts it like this:

when the researchers added in the possibility of a moderate 2 degrees of warming before the end of the century, this led to a decline in future GDP of between 30 and 50 percent by 210 […] In the U.S. alone […] A 50 percent decline in 2100 GDP relative to baseline means a loss of $56 trillion each year, which exceeds the current GDP. Such declines would leave individuals with “a 31 percent drop in purchasing power relative to a world without climate change,” Bilal adds. Such losses are “comparable to living in the 1929 Great Depression, forever,” he says.

https://www.harvardmagazine.com/2024/09/harvard-economic-impact-climate-change

Environmental protection is economical protection. They go hand-in-hand.

I agree that humans are remarkably creative, and I agree “don’t have kids” is reasonable. But the “end of humanity” might come through this. However, I agree that we might be able to survive this. But please take it seriously. The whole climate crisis is a complex challenge by itself, and the politicization of it, along with the capitalistic interests, are complicating it further. We need urgent global action if we want humanity to survive.

Consider: Not all those billions of people will survive the sudden shift in climate. The breaking points in climate make everything super difficult to plan for. It is not just about finding higher ground that is climatic for humans, the whole agriculture will be a big problem. The climate will be so different from what we have right now, we are not perfectly sure how which crops would work where. We need globally aligned tests, knowledge sharing at the very best, along with all the action we need to take along with carbon emissions.

This challenge, is our biggest yet. We need a global, aligned, focused effort. But, we are far from it. The stress is causing conflict everywhere. Our international order is not up to coordinate this global effort, unfortunately. And if COVID-19 showed us what we can have on a global scale as a response, it means every nation state will turn inwards, try to fight against it by themselves while also fighting against everyone else. This problem is the crux. Our systems, our worldviews, our doctrine are not up for this fight ahead.

There is hope. But there is also a lot to despair about.

Human beings are remarkably creative when they need to be.

Yes! Humans say they think children are important, then create situations where children are hungry, abused, or killed in war. Then they create rationalisations for that being inevitable, or acceptable, or even deserved.

Humans also create technology to ‘make the world better’, then use it to convince people as a group to do things which make the world worse.

Aren’t humans creative? They’re going to create a lack of humans eventually - isn’t that imaginative?

Please correct me if I’m missing something here.

Those in power often use crises to invent reasons to take more power, and to direct it against scapegoats. The point is not often to make the world better for everyone, the point is very often to make the world better for those who already have the most.