therisingblues wrote:I never get this argument: because something was natural in the past, mankind cannot be responsible for it now.Psyber wrote:
What do you say then about the similar rise 270 million years ago?
What - or who - put the "sh!tloads of carbon dioxide we (are) putting into the atmosphere" there then?
Anyway, a quick google revealed a couple of theories. The period you are asking about coincides with the Permian age, which ended about 250 million years ago. Wikipedia says it's the largest single extinction event on record. The strongest theory is that it was volcanic.
The following is copied and pasted from wiki:
The final stages of the Permian had two flood basalt events. A small one, Emeishan Traps in China, occurred at the same time as the end-Guadalupian extinction pulse, in an area close to the equator at the time.[96][97] The flood basalt eruptions that produced the Siberian Traps constituted one of the largest known volcanic events on Earth and covered over 2,000,000 square kilometres (770,000 sq mi) with lava.[98][99][100] The Siberian Traps eruptions were formerly thought to have lasted for millions of years, but recent research dates them to 251.2 ± 0.3 Ma — immediately before the end of the Permian.[9][101]
The Emeishan and Siberian Traps eruptions may have caused dust clouds and acid aerosols—which would have blocked out sunlight and thus disrupted photosynthesis both on land and in the photic zone of the ocean, causing food chains to collapse. These eruptions may also have caused acid rain when the aerosols washed out of the atmosphere. This may have killed land plants and molluscs and planktonic organisms which had calcium carbonate shells. The eruptions would also have emitted carbon dioxide, causing global warming. When all of the dust clouds and aerosols washed out of the atmosphere, the excess carbon dioxide would have remained and the warming would have proceeded without any mitigating effects.[93]
Your climate chart over the ages also indicates volcanic activity as the cause of the increased CO2 in that period.
Now these eruptions are believed to have been massive, unlike anything on Earth now. No doubt the occassional volcano goes pop from time to time now, but we haven't had a Krakatoa, Mt St Helens or Vesuvius for a while now, something else is driving CO2 levels up.
TRB, I don't say "mankind cannot be responsible for it now" - nor do I deny that mankind may be responsible for some of it now - I accept we are at least that!
My position is to oppose those who blindly pronounce it is all man made, given that there are substantial natural factors (apart from volcanoes) currently operating too.
(Like the current spike in the Milankovitch cycles due now.)
It worries me that attributing it all to man's activity may mean we think we can fix it all by changing our ways.
That may mean we don't plan for, and prepare to cope with, change that may go on regardless of anything we change in our own contribution.
(Just as we focus on CO2 while we ignore the many other pollutants we pump out that may be more immediately dangerous.)
