There are more than a billion active websites on the Internet today, and each page view consumes 1.76 grams of CO2 in average. This is huge, but only a fraction of the whole ICT industry, which consumes twice more than the aviation industry. And the electricity bill keeps growing.
If we have to start somewhere, it's with software.
Have a look at your website dashboard and figure out how many page views you get per month. Then use a website carbon footprint calculator to give yourself an idea of your consumption level. These generators are not entirely accurate, but they are good estimates to get you started: multiply your number of page views by your CO2 footprint, and you'll know how impactful the change will be.
In my experience, my web applications and sites are in the 0.1-0.2 grams of CO2 per page view after switching to sustainable web technologies. Writelier had 12,000 unique visitors over the last 30 days, so at least this much in page views (I don't track my page views). In other words, dividing my carbon footprint by ten allowed me to prevent at least 18kg of CO2 from entering the atmosphere just last month.
Even though most of the page views come from the top 100 websites, it still matters. 18kg of CO2 is what leaving a LED bulb on for 216 days straight produces, to give you an idea, and Writelier is a small website. Apply the change to a billion websites, and we would save enough energy to light the world for decades.