Arguments
What does past climate change tell us about global warming?
What the science says...
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Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions. |
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Climate Myth...
Climate's changed before
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)
Greenhouse gasses – mainly CO2, but also methane – were involved in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When CO2 levels jumped rapidly, the global warming that resulted was highly disruptive and sometimes caused mass extinctions. Humans today are emitting prodigious quantities of CO2, at a rate faster than even the most destructive climate changes in earth's past.
Abrupt vs slow change.
Life flourished in the Eocene, the Cretaceous and other times of high CO2 in the atmosphere because the greenhouse gasses were in balance with the carbon in the oceans and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels.
Lush life in the Arctic during the Eocene, 50 million years ago (original art - Stephen C. Quinn, The American Museum of Natural History, N.Y.C)
But there have been several times in Earth’s past when Earth's temperature jumped abruptly, in much the same way as they are doing today. Those times were caused by large and rapid greenhouse gas emissions, just like humans are causing today.
Those abrupt global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the Permian, Triassic, or even mid-Cambrian periods. The symptoms from those events (a big, rapid jump in global temperatures, rising sea levels, and ocean acidification) are all happening today with human-caused climate change.
So yes, the climate has changed before humans, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. And past examples of rapid carbon emissions (just like today) were generally highly destructive to life on Earth.
Basic rebuttal written by howardlee
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
Last updated on 6 August 2015 by pattimer. View Archives
[DB] If you liked that video then you should love this one, from SkS author Robert Way:
[DB] If a book is what you ask for a book is what ye will receive:
Spencer Weart's: The Discovery of Global Warming
Highly recommended.
[DB] "Our planet does not have enough free oxygen (O2 as opposed to CO2) for its current population."
Umm, nope. Of all the resources consumed by mankind, O2 is the most ample and in no danger of running out.
Scarce items:
[DB] In the absence of anthropogenic forcings, yes. Since the Holocene Climatic Optimum some 6,000+ years ago the net forcings (without man) have been negative and the overall temperature trend downward.
The long, slow slide back to glacial conditions had already begun. Now evidence shows we have little to worry about (the next cold phase of the ice age cycle).
[DB] "Are there any other likely reasons for the loss of ice we are seeing other than anthropogenic?"
Absent near-mythological musings such as massive volcanic eruptions along the Arctic Ocean seafloor (no evidence), increased submarine patrols under the ice causing turbidity which then causes the ice to break up & melt (huh?) or magical as-yet-undetected cycles...none that I'm aware of. Please let me know if I missed something.
[DB] "when Co2 is high"
See the label on the graph below:
[Source: http://climate.nasa.gov/images/evidence_CO2.jpg]
The last time CO2 levels were as high as now (the Pliocene) the world was a dramatically different place, with much higher sea levels:
[Archer 2006]
I am not aware of any plausible mechanism that would allow formation of an Arctic ice cap during a period of high Milankovich orbital forcings and elevated CO2 levels such as at present.
[DB] And this, then, the most telling graphic of all: