字幕表 動画を再生する 英語字幕をプリント CO2 levels are on the rise but they've been way higher before. So… climate, we cool? Hello everyone, Julian here for DNews. Antarctic CO2 levels finally caught up with the rest of the world and have an average concentration of 400 parts per million. So for every 1 million particles in the air, 400 of them are Carbon dioxide. It's the highest those levels have been in 4 million years. If you're a person who watches DNews regularly you might recognize this as a bad thing, but if you're a “climate change is baloney” type, you may have heard that sentence differently. If this is the highest Antarctic CO2 has been in 4 million years, then 4 million years ago things were like they are now and we still turned out ok, right? Boom, climate change busted. Actually if you ascribe to that argument, I have even better news for you! At certain points in earth's history, like during the mesozoic in the time of the dinosaurs, CO2 concentrations were as high as ten times what they are now. So why's everybody freaking out about a measly 400 parts per million? We asked University of Northridge geochemist Jenn Cotton exactly that. Cotton explained that there are still a lot of things that separate our current situation from the extreme carbon dioxide levels of the past. For one thing, our concentrations are ramping up a lot faster than they ever did before. For most of earth's history the biggest emitter of CO2 was volcanic activity, both on land and below the ocean, but volcanic CO2 emissions are fairly slow and steady. Even during the Paleocene-Eocene Thermal Maximum, temperatures rose 5 to 8C over millennia, not centuries. Of course, as a geologist Cotton describes this as, “a really really rapid warming event,” but her sense of timing is a bit out of whack. This is why there are no geologist comedians. But over that long period of warming organisms adapted to their changing environment and indeed few species went extinct during this period, which some climate change deniers use to downplay the impact of modern climate change. But in fact, the current rise in temperatures is happening much much faster than it did 55 million years ago, and many organisms likely won't be able to survive. Another issue is the average global temperatures do not increase linearly with CO2, there are diminishing returns. Bumping up concentrations by 100 parts per million when it's already at 3000 is not going to cause nearly as drastic a change as if concentrations were at 300 parts per million, like they were in 1910. We're actually at the lower end of atmospheric carbon concentrations right now compared to most of earth's history, which means that the climate is much more sensitive that it has been historically. But if it was so high in the past, won't it just come down again? Yes, climate change denier it will, but again, on a geological time scale. CO2 is taken out of the air when it mixes with water in atmosphere and forms carbonic acid. It's why rain doesn't have a neutral ph of 7, it's typically closer to 5.5 even in the absence of any other pollutants. The carbonic acid reacts with rocks, breaking them down, turning them into soil, and being converted itself into carbonate. So, yes, atmospheric CO2 has been more abundant in the past, but not for millions of years. That Paleocene-Eocene Thermal Maximum probably took 10,000 years to hit its peak, and didn't drop to previous levels until 150 thousand years later. Some people refuse to believe climate change is real because it used to be called global warming, and changing names means scientists must be lying! Unless climate change is used because it's the more accurate name. Trace explains here. What do you think? Think we can turn this climate change thing around in less than 150 thousand years?