How much fuel gets dumped and why?
While according to British Airways estimates quoted in the Inter-Governmental Panel on Climate Change (IPPC) report on “Aviation and the Global Atmosphere” published in 1999 “only a very small percentage (on the order of 0.01%) of fuel used by the aviation industry each year is jettisoned”

https://greentumble.com/environmental-impacts-of-fuel-dumping/