When checking the Product Carbon Footprint for Personal Systems here, you might have noticed, that for Notebooks the "Distribution" value is generally higher than the one shown for Desktops. 

This is due to the fact, that the assumption for distribution is different when calculating the values.

For example, notebooks have a default assumption using primarily air freight, so their distribution values will always be substantially higher due to the emissions associated with air freight.  Desktops, on the other hand, have no assumed air freight, whereas their primary mode of transport is ocean freight, which has significantly lower emissions than air.

PCF 

Product Carbon Footprint

Distribution

emissions 

Notebook

Desktop

air