Disclaimer: This is not 100% sure, this is a bet I'm making. The future will decide
The explanation for me is due to the availability of porn and the usage of dating apps (I include instagram as a dating app). As porno is available in so much quantity without effort, it is much easier for guys to consume sexual content than to find a sexual partner. And for girls the existence of dating apps allow any kind of girl to meet with super hot or famous guys. A girl seeing she can have so much attention from guys even the hotter ones can only shift her expections higher and make it even more difficult for boys to be considered. The results of that (if this is true) is guys and girls having less sex.
There is also the fact that feminism encourage girls to have more freedom, and encourage them to have better career, which means less "being a wife" and thus reducing the need to settle down to have children but also reducing the interest for these girls to need a man in their life.
But this is only the beginning for me. The concept of the metaverse is going to change everything. Imagine the difference between looking at a porn magazine and watching a porn video, this is a pretty good gap in terms of sensations right ? Well the metaverse is going to create the same gap. Many people underestimate the metaverse and feel like this is some crypto, web3 bullshit equivalent. But this is not the case. The concept of the metaverse is to create an immersive environment to make humans better feel the virtual world. Will the metaverse be powered by META ? That's something that is not sure at all, but whether this is META who creates it or someone else will not change the result. If you can have the sensation that your dick is being sucked by your favorite pornstar it is unlikely you will want to spend time trying to find an average girlfriend. Of course having sex is not the only reason people are in a relationship. But would you keep your girlfriend if you didnt have sex with her?
Back to the title of the article. The metaverse will make people not wanting to have sex by a lot. Less sex means less relationships, less relationships mean less babies, less babies mean huge decrease of the world population. Decrease of the world population will create many problems, but as long as the co2 emission per person is not increasing as fast as the world population is decreasing then the total world co2 emission will decrease. This can go pretty fast, if the average number of children per woman is 1 for example then it takes only 80 years for the population to be cut by 50%. If the per capita co2 emission is not increasing (which seems to be the case) then the total world emission is going to be cut by 50% by 2100