Arguments
What does past climate change tell us about global warming?
What the science says...
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Basic
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Intermediate
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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
'....It is obviously true that past climate change was caused by natural forcings. However, to argue that this means we can’t cause climate change is like arguing that humans can’t start bushfires because in the past they’ve happened naturally...' is just another absurd comparision.
Comparing a billions of years old eco system and it's natural forcings over eons, to e.g. two neanderthals rubbing two sticks together 10,000 years ago to start a fire, and then accidently starting a bush fire, (proving that even neanderthals had the ability to change the climate!) demonstrates (-snip-).
pcrudy... It's actually a very apt comparison. It's shown over and over in published research that CO2 is the "Biggest Control Knob" (as Dr Richard Alley puts it) for global climate change.
Essentially, what humans are doing is taking that knob, that naturally modulates, and we're turning it rapidly in the warming direction. So, saying that natural climate change precludes humans being able to change climate is fundamentally wrong. And that is the point of the statement.
pcrudy:
The comparison is quite accurate. Arguing that humans can't drive climate change now because humans didn't drive past climate change - in the face of basic physics, backed by empirical evidence, that they can and indeed are - is logically equivalent to arguing that humans can't cause brush fires because they didn't in the past.
The scale of the behaviour being argued is not pertinent.
Another aspect of the "climate has changed before" argument, not covered off in the current answer, is the implication that current climate change should not be considered alarming. "It's changed before, and yet here we are" may be a fair summary of this version.
Is it worth adding some relevant discussion and cross-filing the argument under both the "It's not us" and "It's not bad" taxonomies?
The main responses seem to me to be that a) deep past climate changes were not much fun for living things at the time, being associated with mass extinctions and great upheaval; b) human societies and economies are adapted to the climate they developed in, and so even changes within the range of natural changes of the distant past would be very disruptive; and c) humans now use a very high proportion of potential quality farmland, affordable freshwater and so on to accommodate a large population with high (for many) or rising (for many) living standards; there is not much safety margin to prevent a loss of living standards if climate change erodes availability of some of the resources we depend on.
What was wrong in what Richard Lindzen wrote?
Mark @345 - there's nothing directly wrong with 'the skeptic argument' as articulated by Lindzen here. It's the implication of the statement where the problem lies. Saying 'climate has changed naturally in the past' is like saying 'humans breathe oxygen'. No duh. Everybody knows that. So what's the point in saying it? The answer to that question is pretty clear.
So the "#1 global warming myth" is not really a myth at all...?
Mark, "the climate has changed" before is mostly used to imply that humans arent responsible for current warming and/or that past changes are unforced. As a skeptic argument, it is framed as an excuse to do nothing. In the source where the quote came from, Lindzen tries to touch both bases, along with an a priori assumption that climate sensitivity is low. He has been trying to find some plausible reason for low sensitivity without much success so far. If you want to get down to real myths, then I guess you have to look at what logical step follows from "climate has changed before" but for many, this somehow seems to be enough.
No. There's nothing wrong with the information itself. The myth occurs when the information is voiced--made public. I'd bet you that in 99.99% of the cases in which those facts are strung together and published, the person doing the stringing is attempting to make an implied argument that since climate has changed before without rapid accumulation of atmospheric CO2, and therefore the current climate change is not the result of human CO2 emissions. I've engaged with at least 400-500 people on comment streams using this very implied argument.
So the answer to your first question is "What's wrong is that Lindzen actually wrote it."
In other words, Lindzen thinks you're stupid or at the very least simply ignorant, and willingly so. If you said to him "Duh! What's your point?" he'd probably bluster a little and then show you some really cool graphs.