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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Climate Hustle

What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions.

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 COin 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 Eocene Arctic 50 million years ago

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 PermianTriassic, 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

Printable Version  |  Offline PDF Version  |  Link to this page

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Comments 551 to 553 out of 553:

  1. too @550...  Pretty much every point you've stated here is fundamentally incorrect.

    1) Many solutions, in addition to wind and solar, are discussed to address climate change. Nuclear, CCS, efficiency, tidal, geothermal, hydro are all solutions which are being actively worked on and are being actively implemented. 

    2) Researchers provide a wide variety of temperature reconstructions for past temperature. There are numberous local and regional records, and there are a great many multiproxy reconstructions as well. Just because something is "inferred" does not mean that it is wrong. That would be a classic case of throwing the baby out with the bathwater. Just because you don't have absolute precisions doesn't mean you can't trust the information you do have.

    3) What we do know about CO2 concentrations is, they are rising. There is no question about that fact. We know how much we extract and burn in terms of fossil fuels. We know concentrations are rising due to human contributions. There is very high confidence on this fact.

    4) If you actually were to spend any time reading scientific research or listen to what scientists actually say, you would realize that uncertainties are core to the message that they present.

    I suspect that your entire comment is posted here mostly as a means to drive traffic to your personal climate denial blog.

  2. About a month ago, I took the Pages-2k graph (last 2000 years of global temperature using tree ring proxies) and roughly calculated the temperature change per century, last 20 centuries, and the standard deviation in this metric for this 2000 year period.  I then took 5-century intervals from the Marcott graph (last 11,000 years, ocean sediment data), calculated the average temperature change per century (over 5 centuries), and imposed the standard deviation I'd gotten from Pages-2k to each of these to calculate my best estimate of the temperature change per century for the 100 centuries prior to Christs birth.  I then applied this same technique to the Shakun graph (last 20,000 years).  However, in that case I  used 10-century intervals to get the average temperature change per century and imposed the Pages-2k standard deviation upon that average to get 10 data points representing the likely variance over them.  At the end of all this activity, I had 219 data points representing the likely temperature change per century for the 220 centuries (22,000 years) before the 20th century.  The average was 0.014 C/century, the standard deviation was 0.077 C/century, so the 3-sigma point is 0.24 C/century.  Warming in the 20th century was 0.78 C/century.  To me this proves, statistically, that modern warming is nothing like anything that has occurred in the previous 22,000 years.  Its about 3 times what would be considered extremely unusual from the natural record.  And warming in the last 25 years, if it continues, is about 3 times that again (2.2 C/century).  My question is: does anybody know where this kind of analysis has been performed in the Science record?  I'm sure it has, and to a much greater degree.  I just want to know where to find it so I can refer to it whenever somebody claims 'Its all natural'.

  3. Excellent article new at RealClimate: "The climate has always changed. What do you conclude?"

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