I know it’s unacceptibly high, whatever the figure is. I would like to have a credible accurate CO₂ cost of a Google reCAPTCHA for comparison purposes and also to add weight to my complaint when condemning a CAPTCHA pusher for their anti-human tech.
update:
A study has just emerged showing that traffic resulting from reCAPTCHA consumed 134 Petabytes of bandwidth, which translates into about 7.5 million kWhs of energy, corresponding to 7.5 million pounds of CO2.
I am just some random stranger on the internet. That is not a credible source to reference particularly if I am the same person giving the citation.
If you work it out yourself you just have to show your working, no need for a citation.