US imports represent approximately 14% of GDP, exports is about 11%. So net imports represents about 3% of GDP. Assuming emissions are roughly proportional to spending the US is exporting 3% of its emissions.
> Assuming emissions are roughly proportional to spending
But without more info, that seems like a pretty awful assumption. A lot of the stuff we export are services and high value goods that I would think have a relatively low "emissions to value" ratio compared to the lower value manufactured goods we import.
Because it's not an even split. Sure, I could buy that, on average, energy use grows in proportion to economic growth, but some activities (e.g. services) I'd expect to have much less energy use that others (e.g. manufacturing).