Let me offer an alternative point of view. Yes, the climate will be irreparably damaged. Yes, lots of humnas will suffer. These things seem to be unavoidable. The harm to both our planet and its citizens is happening as we speak. However, the scale to which this occurs is in our control.
This is an all-hands-on-deck sort of scenario. Everyone will need to pitch in, whatever they can, however they can. Travel less internationally. Reduce (or eliminate if possible) your meat and animal product consumption. Buy less. Vote for candidates that support renewable energy and environmentally friendly initiatives. There's a thousand ways an individual can help by voting with their wallet, their time, and their participation in their political system.
Everything you do, every choice you make today and for the rest of your life, potentially affects the lives of future generations. In my opinion, the most harmful thing you can do, is choosing to do nothing.
Edit: Seeing this is Hacker News, I know a lot of people are going to be commenting with technical suggestions - lab grown meats, renewable energy sources, carbon capture, geoengineering etc. I am very much in favour of these solutions. However, (as far as I know) none of these currently exist at such a scale or level of sophistication so as to make my initial point irrelevant.
I disagree. Millions of Americans and one of two major political parties are actively obstructing action to mitigate the impact of climate change.
Doing nothing is better than doing things to actively hamper positive efforts.
That said, I think my initial point still stands: Everyone needs to do what they can to both reduce their own impact, and to pressure governments and corporations to reduce theirs.
Be the change you want to see in the world.
Even if it was reversible, that would require a negative carbon economy and completed rebuild energy structure that rely upon massive scale zero-carbon energy sources (currently only hydro and nuclear qualify at that scale but either not practical or facing opposition, solar/wind/tidal/geothermo don't). And, a massive scale carbon collecting infrastructure to significantly capture the greenhouse gas in the atmosphere. Unfortunately that technology doesn't exist (at least not outside of the labs or proven scaling massively yet).
There is only so much everyone can do - using LED lighting, reduce energy consumption etc. but without a coordinated political will and a major driving force in technology, it's fruitless. And most importantly, it's too little too late.
Put it simply, there is simply no technical solution and daily habits can change the trajectory of an extinction event. Now it's clearer than ever why Musk and Bezos are exploring space and Mars colonization given their tremendous amount of fortune and resources behind their teams of smartest people working for them - rather than say saving our planet and happily ever after.
Lastly, I still believe in doing something is better than nothing, that's the only positive aspect of this story.
The real issue is that nobody has proven this wasn't going to occur anyway. This is always the downfall with climate science in that there is no explicit proof that anything man does to the planet would alter what was going to occur anyway.
Climate scientists also have an agenda to keep their funding so will never say "there is no issue" but will always point to the inevitable as it matches what they want for a conclusion.
Follow the money, as they say.
Are you saying that the contribution of CO₂ levels to warming isn't established, or that the human role in increasing CO₂ levels isn't established? Because both of those are very well established.
> This is always the downfall with climate science in that there is no explicit proof that anything man does to the planet would alter what was going to occur anyway.
This is only true in the sense where “explicit proof” is restricted to pure abstract domains like math and not applicable to any domain of material fact; to the extent that it is possible to “prove” anything about what would happen in counterfactual alternative conditions in the material universe, though, this has been proven.
No one has proved that mankind’s contribution is material to the underlying trend, nor proved that warming will be as bad as claimed. So what if Greenland becomes green again?
Established by who and where is their funding coming from? Would you trust a survey that says "Windows is better than Linux" if it was funded by Microsoft? That's why where the funding comes from is key.
> is only true in the sense where “explicit proof” is restricted to pure abstract domains like math and not applicable to any domain of material fact; to the extent that it is possible to “prove” anything about what would happen in counterfactual alternative conditions in the material universe, though, this has been proven.
If you want hundreds of billions of dollars to be invested in something which hasn't got clear proof of value then that's simply not enough. You need to prove the Return On Investment, regardless of field. It all comes down to money.
The less important part for me: "...this will happen because of the human activity that they cannot stop anyway".
So my idea is to prepare for this scenario, because we cannot realistically prevent it. E.g. build dams where it makes sense, evacuate the dangerous areas where protection cannot work, predict in detail what the coastal map is going to look like, try to predict how ocean currents and winds will change, and prepare to that, etc.
This article has more written about
monetary incentives of climate scientists: https://arstechnica.com/science/2016/05/if-climate-scientist...
"There is high agreement that cost of stratospheric aerosol
injection (SAI) (not taking into account indirect and social costs, research and development costs and monitoring expenses) may be in the range of 1–10 billion USD yr–1
for injection of 1–5 MtS to achieve cooling of 1–2 W m–2 (Robock et al., 2009; McClellan et al., 2012; Ryaboshapko and Revokatova, 2015; Moriyama et al., 2016), suggesting that cost-effectiveness may be high if side-effects are low or neglected (McClellan et al., 2012)." 
Some of the other options are outlined in Table 4.7 of the report. Given that these are not that expensive and could radically reduce temperature, I think we should be doing a lot more to research both the intended and unintended consequences. I strongly think some entity is going to try some of them, and some have already been done by folks: https://www.nytimes.com/2012/10/19/science/earth/iron-dumpin...
If you are interested in mitigating climate change, I encourage you to read through chapter 4 of the IPCC report which covers many of the possible methods.
 Chapter 4 of the IPCC report; http://report.ipcc.ch/sr15/pdf/sr15_chapter4.pdf
Also, melting of enough of Antarctic ice may raise the level of oceans so much that protecting coastal cities with dams will become impractical. That is, whole countries, like the Netherlands, currently have a lot of their territory below sea level, and had for centuries. But this only works for a difference of several meters, but is unlikely to work for e.g. 50m.
People are not going to get off their cars and hop on a bike.
There is something you can do, today, to mitigate one of the biggest causes of climate change.
Give up meat and dairy.
Ironically the thing that is easiest to do is also the last one people want to do.
I always thought that the fight against meat and dairy was a moral one. I didn't know the toll it takes on the environment, until I specifically went looking for it. It is one of the best kept capitalist secrets.