We're going to have to engineer the climate directly if we still want to have an industrial society in 200 years. We will probably do it much sooner. The effects of the combination of more CO2 + artificially decreased sunlight are going to be bad, but are not well understood.
It is true, it's not a question of whether we have consequences or not, just a question of "how bad". That is extremely strongly a function of how much emissions we emit until, say 2050. It's hard for me to even imagine how we can continue using fossil fuels for energy much beyond then, so not reducing emissions also strikes me as kind of... needless self-inflicted harm.
When you say 'It is not a question of whether we have consequences or not, just a question "how bad"', it sounds like 100% confidence, but then you say that it is not 100%. So is it more like >99%? Or 70%? Or 10%? Or <1%?
And more specifically, what is the probability that reducing anthropogenic emissions to a certain target would result in us averting the predicted catastrophic scenario that otherwise would not have been averted?
Sea levels are rising due to the melting of land ice. That's a historic fact, but predicts are concerned with how much it will rise. There is a chance that it will reverse, and before 100 sea level will actually fall. How much probably depends on what factors you allow yourself to consider. For example, I think the most likely reasons this would happen would be due to human geo-engineering or nuclear war. For that, maybe I'd give 0.01% chance. But for it to change course due to natural factors... I'll give 1.0e-6%. Because you know, about every 100M years sounds reasonable for a sudden violent and unprecedented climate movement in Earth's history. The reason this is so tremendously unlikely is because the climate is already hot enough to melt most of the ice, only reason it hasn't is because it takes time. It's a system that's moving on (an abstract form of) inertia.
> reducing anthropogenic emissions to a certain target would result in us averting the predicted catastrophic scenario that otherwise would not have been averted?
I honestly can't read this. Rising sea levels affects people... the more it rises the worse it is. At some point, the rise is catastrophic. The English language is not going to help say "at exactly 1.65 meter rise it becomes catastrophic".
Climate scientists can, and do, connect emissions scenarios to a sea level. It's a much more human activity to connect the change in environment given by a numerical metric to a moral judgement.
Carbon emissions are mostly from transportation and energy production - neither of which are goods. Both have more sustainable alternatives that a carbon tax would easily push people to use via market forces.
The relationship between tailpipe carbon emissions and temperature, and then sea-level rise, is absurdly strong scientifically speaking. Energy accounting is a very hard science. We know what IR bandwidths CO2 gas absorbs, and that translates directly to an additional heat flow. We are watching the northern sea ice disappear because of carbon emissions, and we will witness much more. The most stinging effects will be reduced agriculture output, direct temperature rise consequences, and sea-level rise. The consensus science on sea-level rise (see IPCC) results in extremely quantifiable economic damage within this century, and those are low-ball numbers. The confidence level is simply "confident". There is no reasonable question that things will be as-bad or worse than the consensus predictions. There are reasonable questions about low-probably chances that things will get much, much, worse.