At this point, using Firefox and an ad blocker does more for the climate than paper straws or recycling.
Even with ad blocking, half of consumer internet traffic is ads. Google is contributing to increasing this ratio, where most traffic on the internet will be stuff the client did not request, contributing more to climate change than Bitcoin - not that this makes crypto look better, they are just a useful milestone to compare to with the press they get.
And this doesn't include the idiotic AI shit they do.
I'm pretty sure the traffic for the ads still gets sent to your device over the Internet, it's just that the ad blocker keeps it from rendering in your browser.
It's a mixed bag. Some ads (like some Youtube stuff I guess) are bundled and filtered, but most actually rely on external requests to ad exchanges. What happens mostly is that when there is an ad spot in the page you downloaded, that is in fact a generic request to an ad broker to send an ad instead of a specific ad. That then starts a real time bidding process inside multiple broker networks to find the most expensive (for the advertiser) ad they can show you based on your tracking information and demographics.
And that's for every ad spot. It's insanely intricate and frankly wasteful.