Well the black comes from microscopic soot particles. So it depends on what you mean by "worse environmentally" . From a global warming perspective your right it is not much worse. From a PM2.5 particulate emissions perspective it is much much worse for the people who breathe in the soot as it can cause cancer and other lung issues. This is why in Europe they are starting to ban diesel cars in cities due to escalating health related PM2.5 issues (https://www.express.co.uk/life-style/cars/925353/Germany-diesel-ban-fuel-Europe-cars). It is the contrast with the pristine alpine environment here which makes it interesting. As a process/chemical engineer I love the fact this steam unit is still operational ; but in this day and age it is hard not to see it as environmental vandalism I think.