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It's the first time I've heard that CO2 levels previously in history were at the same level as now, so I asked a genuine question. This thread is starting to g

It's the first time I've heard that CO2 levels previously in history were at the same level as now, so I asked a genuine question. This thread is starting to get as ridiculous as a Trump thread. Any shadow of questions that don't fit exactly with the echo chamber and you instantly get vilified as the devil, or a Trump supporter, even though I didn't espouse any climate-denier comments.

JoeAltmaier 10y ago
Its a reasonable issue - historic (estimates) of CO2 levels were not out of line with current levels. Yet historicly the world's ice hadn't melted. Is something else going on? Perhaps in concert with rising CO2?
- mikeash 10y ago
  "History" is a misnomer here. That term is usually used to refer to the time since the invention of writing, roughly 5,000 years ago. CO2 levels have never been anywhere close to current levels in that period. CO2 levels have been this high, and much higher, in the distant past. But the climate has also varied enormously in the distant past as well. Roughly 55 million years ago, the planet had nearly no ice. A bit over two billion years ago, it's believed that the planet was almost entirely covered in ice. So no, it's not really a reasonable issue. CO2 levels have varied a great deal, as has the climate. Nothing in the Earth's climate past suggests that the current dramatic rise in CO2 levels wouldn't also result in dramatic changes to the climate.
  - JoeAltmaier 10y ago
    But isn't it the case that CO2 levels could not be seen as a direct indicator of ice levels in say the last 35 Million years? The ice-free times correspond to high CO2; the icebound times to low CO2. But in between there's considerable difference, and no simple correleation. One could be driven to think, something besides CO2 is (also) involved.
    - mikeash 10y ago
      I don't know enough about it to know whether it is as you say, but nobody denies that climate feedback loops are extremely complicated and there's rarely a direct relationship between any two numbers.
    - nickjarboe 10y ago
      In recent geologic time CO2 levels seem to mostly be influenced by temperature instead of increasing CO2 levels causing temperature rise like today (there does not seem to be animals in past all of a sudden excavating and burning gigatons of carbon annually). Over million year timescales the biggest cause in the change in Earth's temperature is Milankovitch cycles[1] which is short hand for changes in the shape Earth's orbit and changes in the position of the Earth's spin axis. These changes interact to produce various climate conditions. The biggest factor is that sometimes these cycles cause the northern hemisphere to have very cold winters and other times mild winters. When the winters are very cold, continental glaciers can form on North America and Eurasia. They reflect more sunlight than land and the Earth gets colder. This is an ice age. Eventually the orbital and spin axis parameters change (over tens of thousands of years) and, with warmer winters in the northern hemisphere, the ice sheets begin to melt. With this positive feedback loop, the ice age ends quickly, the Earth gets warmer, and the Earth enters what is called an inter-glacial (we are in one now). This is, of course, a very simplified explanation. As one goes back hundreds of millions to billions of years, other large scale changes like plate tectonics, atmospheric composition/mass, sun brightness, continental weathering, etc. will cause the average surface temperature to vary considerably. [1]https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles
FullMtlAlcoholc 10y ago
We really need a corollary to Poe's Law known as Trump's Law. BTW - No one brought up the spectre of Trump, you invoked it. People are, rightly, criticizing your gut feeling that flies in the face of our best understanding of multiple hard scientific fields and the tons of works and dedication by tens of thousands of researchers around the globe.
- pfarnsworth 10y ago
  My point is, if you say something that doesn't completely damn Trump or say something that can be interpreted as even being mildly positive towards him, all of a sudden you're attacked as a Trump supporter. It's ridiculous. Same goes for climate change. I didn't say anything that denied climate change and yet look at the comments above. Sure, the ice levels are outliers this year, but I think they'll probably revert to the mean in a couple of years. Just like the CA drought. And yet all of a sudden I'm a climate science denier? It's stupid and idiotic.

JoeAltmaier 10y ago

Its a reasonable issue - historic (estimates) of CO2 levels were not out of line with current levels. Yet historicly the world's ice hadn't melted. Is something else going on? Perhaps in concert with rising CO2?

mikeash 10y ago
"History" is a misnomer here. That term is usually used to refer to the time since the invention of writing, roughly 5,000 years ago. CO2 levels have never been anywhere close to current levels in that period. CO2 levels have been this high, and much higher, in the distant past. But the climate has also varied enormously in the distant past as well. Roughly 55 million years ago, the planet had nearly no ice. A bit over two billion years ago, it's believed that the planet was almost entirely covered in ice. So no, it's not really a reasonable issue. CO2 levels have varied a great deal, as has the climate. Nothing in the Earth's climate past suggests that the current dramatic rise in CO2 levels wouldn't also result in dramatic changes to the climate.
- JoeAltmaier 10y ago
  But isn't it the case that CO2 levels could not be seen as a direct indicator of ice levels in say the last 35 Million years? The ice-free times correspond to high CO2; the icebound times to low CO2. But in between there's considerable difference, and no simple correleation. One could be driven to think, something besides CO2 is (also) involved.
  - mikeash 10y ago
    I don't know enough about it to know whether it is as you say, but nobody denies that climate feedback loops are extremely complicated and there's rarely a direct relationship between any two numbers.
  - nickjarboe 10y ago
    In recent geologic time CO2 levels seem to mostly be influenced by temperature instead of increasing CO2 levels causing temperature rise like today (there does not seem to be animals in past all of a sudden excavating and burning gigatons of carbon annually). Over million year timescales the biggest cause in the change in Earth's temperature is Milankovitch cycles[1] which is short hand for changes in the shape Earth's orbit and changes in the position of the Earth's spin axis. These changes interact to produce various climate conditions. The biggest factor is that sometimes these cycles cause the northern hemisphere to have very cold winters and other times mild winters. When the winters are very cold, continental glaciers can form on North America and Eurasia. They reflect more sunlight than land and the Earth gets colder. This is an ice age. Eventually the orbital and spin axis parameters change (over tens of thousands of years) and, with warmer winters in the northern hemisphere, the ice sheets begin to melt. With this positive feedback loop, the ice age ends quickly, the Earth gets warmer, and the Earth enters what is called an inter-glacial (we are in one now). This is, of course, a very simplified explanation. As one goes back hundreds of millions to billions of years, other large scale changes like plate tectonics, atmospheric composition/mass, sun brightness, continental weathering, etc. will cause the average surface temperature to vary considerably. [1]https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles

FullMtlAlcoholc 10y ago

We really need a corollary to Poe's Law known as Trump's Law. BTW - No one brought up the spectre of Trump, you invoked it. People are, rightly, criticizing your gut feeling that flies in the face of our best understanding of multiple hard scientific fields and the tons of works and dedication by tens of thousands of researchers around the globe.

pfarnsworth 10y ago
My point is, if you say something that doesn't completely damn Trump or say something that can be interpreted as even being mildly positive towards him, all of a sudden you're attacked as a Trump supporter. It's ridiculous. Same goes for climate change. I didn't say anything that denied climate change and yet look at the comments above. Sure, the ice levels are outliers this year, but I think they'll probably revert to the mean in a couple of years. Just like the CA drought. And yet all of a sudden I'm a climate science denier? It's stupid and idiotic.