Chrome is used by about 3.8 billion people [1]. So, if this is rolled out to every chrome user over the next year or two, this would generate about 15 Exabytes of traffic. It's difficult to find accurate, useful numbers on this, but lets assume 29 grams of CO2e per GB, this would be about 450k tons of CO2e. This in turn, equates to average household CO2 expenditure of almost 300k households.
So make your own judgement, but this seem pretty significant to me.
Did you notice when your streaming files went from 1.5 GB for a movie to 6 GB for a movie? I didn't. Almost no one does. And no one writes blog posts like this about the data usage.
29 grams for something that takes most folks less than 20 seconds to download? How many watts (neglecting the machinery was going to be running regardless of whether you are transferring something!) do you think it takes to transfer data?
Traffic is not homogeneous in total transfer cost. CDN-hosted data at the edge, close to the user is much cheaper than data that has to transit many hops. At the asymptote, transferring data between machines on the LAN is essentially free.
So make your own judgement, but this seem pretty significant to me.
[1]: https://www.aboutchromebooks.com/global-chrome-user-base/ [2]: https://www.iea.org/commentaries/the-carbon-footprint-of-str... [3]: https://www.anthesisgroup.com/insights/what-exactly-is-1-ton...