"Getting into the spirit of Glasgow I see! Brilliant. Although, probably best to avoid the fried Mars bars if you value your digestive system Greta," tweeted one social media user.
Greta was not given a formal invite to the conference.
The climate activist mentioned a "heavily subsidised" plant which is the third biggest CO2 emitter in Europe and said that despite this, the UK government "still considers itself to be a global climate leader".
The "wonderful" and "uplifting" video has been shared widely across social media - including by Rick Astley himself.
It is fair to say she isn't very enthusiastic about it...
"This is the best thing I have ever seen on abortion," wrote one Twitter user.
The teenage climate activist said no countries in the global north "are even doing close to what is needed".
"Pointing at other countries and this whataboutism isn't going to stop climate collapse," wrote one Twitter user.
The 18-year-old also said the last time she bought a new piece of clothing was three years ago – and that it was second-hand.