On average, a page view emits 0.3 to 0.5 gCO2e from the data centre and network alone. Once the user's device and the amortised manufacture of the equipment are included, the figure is closer to 0.7 to 1.5 g. Between a very light page and a heavy one (about 8 MB for the heaviest 10% of mobile pages), the difference easily exceeds a factor of 10.
Read the source article: Website carbon footprint: how to calculate and reduce it