More than 100% of observed warming is due to human activity.

Why?

Because according to natural factors - the sun, orbital cycles, and volcanoes - the planet should be cooling right now. So human-induced warming is (a) causing all observed warming right now, and (b) offsetting natural cooling, too.

For more information, watch:

And for all the details, see Chapters 1–3 in the Fourth US National Climate Assessment, here: science2017.globalchange.gov