[Sigh.] The ice core data is part of what establishes the fact that CO2 is warming the atmosphere and the planet.
I've come to understand CO2 is a minor GHG.
In a sense, it is. Methane for example is far more powerful than CO2 in that regard. But methane has a residence time of only about 12 years, while CO2 lasts for longer than a century. Methane breaks down into CO2 and water vapor. Water vapor is more important than CO2 in some ways too. But it is transient (residence time of only one to two weeks), and it is a feedback rather than a forcing.
Its been far higher in the atmosphere in the past (hundreds of millions of years ago) than at present.
True enough. And the earth has almost always been warmer in the past than it is in the present.
Citing the last 400K years or 2M years means citing a period dominated by ice ages.
This is true as well. But the point is that civilization has taken place in an interglacial within that ice age. What makes climate change dangerous today for humans is that we are interrupting that interglacial, and melting the ice caps, raising ocean levels and increasing ocean acidification (thus threatening life within the oceans which many of us depend on for food), and generally speaking unwittingly conducting a gigantic experiment on ourselves and the climate. For most of the existence of the earth, there has been no or very little ice. Nothing wrong with that--except that not having it will mean that the cities we have so laboriously built up on the shores of the oceans will be inundated as they rise, as will fresh water aquifers. It will also freshen the oceans, especially the North Atlantic nearer term, and play games with the thermohaline circulation, which is an essential driver of climate and transporter of heat from the tropics to what are now temperate regions, but which will become much colder without the circulator. It will also change wind patterns, increase the intensity and possibly the frequency of hurricanes/cyclones and extreme weather events generally, increase desertification and drought in a number of places (including the US southwest and Mexico), make our dams even more unusable as evaporation is intensified, etc. You've heard the litany, and tire of it, I'm sure. So do I. But the difference is that I think it will actually happen, whereas you apparently don't.
I am also struck that examination of global temperatures and CO2 concentrations in ice cores show CO2 increases have FOLLOWED temperature increases, not preceded them. The opposite would be the case if CO2 was a driver of temperature.
Increases do follow warming. They also precede some warmings. What the people who cite this miss is that there are forcings and there are feedbacks. Consider what happened about 55m years, the PETM (paleocene-eocene thermal maximum). Massive volcanic eruptions put more CO2 and methane into the atmosphere. The earth warmed up. The warming led to more CO2 and methane due to dying flora in the oceans and on land, and greater evaporation of water, meaning more water becomes vapor in the atmosphere leading to a still warmer atmosphere. Eventually the oceans became warm enough to release methane clathrates in the deep ocean which releases still more carbon and methane, leading to still greater warming. It is a chain reaction that was forced by something different added that upset the balance that had existed.
That is why CO2 is important today. It is the thing that is being added in massive amounts that is upsetting the balance that is leading to the added warmth and climate change. Read the essay I cited in my previous post. Or read some of the other essays that Weart wrote on the same site (it is his site). Or read a nice book called Frozen Earth, written by an earth science scientist for non-scientists, which also focuses on how we know what we know about climate generally and past climates, focusing on ice ages. Not only ice cores, but ocean sediment cores, fossil analysis, pollen analysis, shell shell analysis, tree rings, etc.
What we ought to be doing if we could actually control our energy usage is saving our fossil fuels for the time when the glacial stage of the ice age returns, and put enough into the atmosphere to warm things up--i.e., keep the level of CO2 in the atmosphere in the high 200s ppm--that would maintain conditions to make earth generally livable for humans and the species that we are comfortable with.
Doing business as usual and allowing CO2 to build up to a thousand or more ppm won't mean that all life will disappear, or the earth will be destroyed. It is that human civilization will be destroyed. It will be impossible to simply adapt to the rising ocean levels and the destruction of life that will take place. Some humans will undoubtedly survive--we are a pretty clever bunch, and have survived some very brutal conditions in the past, although usually those conditions have been much colder not much warmer than present--but we will plausibly have to start over as far as civilization goes.
Well, even as I write that, maybe there will continue to be outposts of learning and civilization in higher latitude climates like Canada where there is plenty of water. I don't know. Above my pay grade. But it will mean a lot of suffering and death for a number of years.
What makes CO2 important today is that we are adding large amounts of it to the atmosphere. it is the forcing that is destabilizing the climate. |
