From what I understand of their response, LTM also made an aesthetic choice to make the images more striking in their old-school look. They chose the look to draw attention to the images themselves. While I think that's fine for Low Tech Magazine, I'm not sure if I agree with that becoming the most generalized result.
(I really like tha approach of kirby though)
Situations like this are why the FSF makes a big deal about distinguishing between the terms "open source" and "free software."
Software like this is known as "source available" because you can read it, but you're not allowed to use it freely.
If you want to make a web site that loads and renders quickly even over slow network connections and on low-resource hardware -- ostensibly the goal of the Low Tech solar website and of this derivative site -- there are better examples to imitate that don't mention carbon dioxide at all.
These sites' main offense against efficiency is the use of small-palette indexed images with heavy dithering. Dithering impairs efficient image compression. Many of the images on this page and on the solar Low Tech site would be more efficiently represented as non-dithered indexed images, perhaps using a larger palette to compensate for the lack of dithering. That's what should have been done with all the charts and text-heavy screenshots. They would look more like the source image and require fewer bytes for storage and network transfer. As it is, this "low tech" page loads 380 kB of PNG images. It's especially egregious when the source image is obviously a continuous-tone photograph, like the image at the top of the article. It should have stayed as a JPEG.
I'm reminded of Intel's environmentally dubious installation of wind micro-turbines on the roof of one of its campuses a few years ago:
In 2015 small wind turbines were already known to generate far less energy per dollar and per unit area than small solar arrays. Intel didn't need another experiment to determine if small wind is better than small solar. The rooftop already had a small solar array. Why didn't they just add more rooftop solar?
The answer is in the photographs about the turbine project: the small turbines stick up over the edge of the roof and would be visible from the ground. The superior solar array is not visible from the ground. The superior option is an invisible commitment to environmental considerations; the inferior option is a visible commitment.
Low Tech magazine (and now its imitators) are embracing a technically and environmentally suboptimal web design approach to ensure that you see their environmental commitments all the way from the parking lot.
To be fair to lowtech magazine, the author does walk the walk, their office setup is powered off solar panels perched on the window ledges .
So I would hesitate to say it was green washing, rather than than just not finding the best compression technique.
I find it at least a bit difficult to believe that either Low Tech Magazine or Gauthier Roussilhe simply don't know any better about optimizing images for compactness at this point. Surely someone has tweeted advice to them even if they didn't originally know. Maybe that's my own failure of imagination.
They do ask for feedback on improving the energy efficiency of the website but viewing it only as a series of optimisations is a very narrow view. The broader context is much more interesting.
The solar powered website, to me feels like an experiment, so I'm not sure its fair to require it to be 100% 'correct' first time.
That should be possible at 500kb uncompressed data, without delays being noticeable.
I suppose then you would need to calculate the power cost that that would impose on the client.