I was quite shocked when I ran the cnet hybrid cars buying guide calculator and discovered how much carbon [something like 5 lbs] my Subaru Forester is injecting into the air annually, above what a hybrid would. I also took the 'carbon footprint' test and discovered that despite driving over 4000 miles a year and running a lot of tech equipment, I have a very minimal carbon footprint---the 'average' was over a hundred pounds a year, which if you multiply by all of us, is a whole lot.
This isn't the only episode human civilization has had with climate change and pollution. The natural drying since the last ice age has widened the Sahara: in Roman times it was possible to walk in the shade from Gibraltar to the Nile Delta: now of course it's desert. So the planet has lost that broad greenbelt that kept the Med's air cleaner---while much of Europe's north was forested; that was cut down by charcoalers in the middle ages, etc, and put into the atmosphere. Or hewn off the Scottish isles by shipwrights; the massive timbers of Scandanavia are only seen now in historic houses: they're gone. So Europe was pretty well deforested over a 500 year span, and a lot of that was burned even before we began excavating the Carboniferous Era forests [coal seams, oil shales] to start burning those---we'd run out of the green-growing sort. So the next 500 years were pretty dirty, and the footprint of a Londoner in the 1880's was pretty sooty.
We've gotten better in that regard: as late as the 1960's, London air would blacken your nostrils and your handkerchiefs, and it hurt the lungs on some days. I was there, and remember having to be careful touching anything white if I hadn't washed my hands. Now they're replanting the lost forests of the Hebrides and trying to reforest some areas in Europe, but in the meanwhile, worldwide demand for materials and increased population in formerly sparsely inhabited areas has entrepreneurs deforesting the Pacific isles and the much larger Amazon at an even faster rate, so it's still a net loss. It's not just the loss of species: [Lord knows what species, beside the last European aurochs, we annihilated in the European forests]---it's the loss of green-space that does the O/C02 cycle, and helps take the carbon out into more biomass. Pound for pound, we're doing way better in some areas, and thankfully we're cleaning up some of the real Cold War era messes like some of the mining towns in Poland---but the net trend is still toward bigger and bigger emissions [burning not only this century's forests, but the forests of millions of years of pre-human times, all at once] and toward less and less greenbelt, be it part of the post Iceage drying or the action of man. It's a bad intersection of our habits with the natural cycle of ice ages and dry-outs. We're collectively not quite as bad as the dino-killing meteor strike---hard to compete with a global firestorm--- but we could do better.
