This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
Objection:
It was even warmer than today during the Holocene Climatic Optimum without any human influence.
Answer:
Actually, it turns out that though there may have indeed been some temperatures in the same range as today, this was regional to the northern hemisphere and confined to the summer months! What's more, the cause is understood (orbital forcing similar to what controlled the Ice Ages), just as today's cause is understood (CO2 emissions), and these causes are very different. NOAA has a page on this which contains the following quote:
"In summary, the mid-Holocene, roughly 6,000 years ago, was generally warmer than today, but only in summer and only in the northern hemisphere. More over, we clearly know the cause of this natural warming, and know without doubt that this proven "astronomical" climate forcing mechanism cannot be responsible for the warming over the last 100 years."
As an aside, it is worth noting that even if this time period had been as warm or warmer, it would do nothing to undermine the theories and data that indicate today's warming is rapid and anthropogenic.
This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.
"It was Warmer During the Holocene Climatic Optimum" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.
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about these higher temp and higher co2 concentration past cycles.
the fact that they cooled at the end of the solar forcing proves that co2 must have less influence on temperature rise than the solar forcing itself.
Posted by: mobihci | May 21, 2009 7:30 AM
How so? That is quite a broad generalization. More reasonable might be that this shows that the solar forcing at those times was stranger than the GHG forcings at those times.
The CO2 changes we are talking about during the Holocene were in the neighborhood of 30 ppm, IIRC, this century we have seen over 100ppm increase.
That said, the sun clearly is the climatic powerhouse, but it is not changing irradiance levels now, or since the early 20th century, at which time it contributed about 30-50% of the warming.
Posted by: coby | May 21, 2009 10:51 AM
solar forcing cannot apply negative pressure on temperature only positive. it wont matter how much solar forcing drops, if co2 forcing was higher (presuming positive feedback) than the solar, then the temp would never drop from the peak again.
i am not just refering to one period of time, the time period doesnt mean anything, it is obvious one way or another through proxies/ice core data etc that temps have been higher in the past and co2 has been higher.
Posted by: mobihci | May 21, 2009 5:14 PM
If solar irradiance drops, then the temperature will drop (all other factors being equal). Just ry comparing nighttime and daytime temperatures. I am not sure what your logic is here.
Posted by: coby | May 21, 2009 6:27 PM
talking about temperature change.
when temperature rises by x deg ie increase in solar forcing, the co2 component of that is added to calculate the overall temp rise for that period.
in a positive feedback system, the increase in co2 heating is a multiplication or amplification >1 if you want to look at it that way. eg in faq at realclimate for the 800 year lag, they say that it is possible that 5/6 of the total heating was caused by co2 in that cycle ie multiplication or amplification level of 5x (eventually).
if you take that to a higher temp than todays at a higher co2 level, then for cooling to have occured there would have needed to be a negative force. note the word force. there is no such thing as a negative force. there are negative feedbacks, but not force.
the conclusion is that negative feedbacks must be greater than positive and this also leads to the solar forcing being greater than the co2 forcing.
please, do tell where the logic is wrong
Posted by: mobihci | May 21, 2009 7:21 PM
I agree with mobihci here. It does tell you that current temperatures won't create a runaway positive feedback loop that will break the world, because it didn't happen before.
Anyway, I've been a climate change skeptic and I'm reading your articles here, Coby. I just have to say I am very impressed so far with the evidence you have presented so far and will be continuing to read more in the future.
Posted by: Jeffrey E. | September 26, 2009 9:13 AM
That's unfortunate, because his posts make no sense at all (coby nailed it in his response, including pointing out that the logic isn't discernable).
Climate scientists don't expect a runaway positive feedback loop due to physics, not past history. The past alone can't give us solace necessarily (look up the Faint Sun Paradox, for instance - the sun's gotten hotter over the lifespan of the earth).
Along with Coby's writings, you might want to check out The Skeptical Scientist and the "start here" button at Real Climate.
Posted by: dhogaza | September 26, 2009 10:07 AM
The problem I have with both "sides" is that you speak in definitives--as if you "know" what happened and why...
You link a page that shows warming or you link a NOAA page that shows something about a warmer period about 6000 years ago.
We are still not looking at global temperatures over geologic time. While we are concerned with the "now," we should put it into perspective... Global warming is not "bad" per se, it is just different from what Man has known in the past. If the warming was caused by normal orbit issues (shape, wobble, etc.), wouldn't it still be just as important to us as people who live on the coast and enjoy skiing?
Again, we can document warming. We can, based on previous temperature data, expect to see continued warming. Limiting greenhouse gasses may limit impacts to our infrastructure, our interests, our ...
It isn't about "proving them wrong"--whoever they are. Remember, at one point we all thought the earth was round, and if we had simply "tried to prove them down," we might not be here today... I don't mind you providing links that help people to talk to "nay sayers." However, provide geologic time scales, provide data that is widely accepted and then talk about why we should limit emissions.
Is it that your argument needs to be right or is it that we might want to be limiting our impact on the planet and the temperatures on the planet regardless of what is causing the rise in temperatures?
Again, if the warming was caused by normal orbit issues (shape, wobble, etc.), wouldn't it still be just as important to us as people who live on the coast and enjoy skiing?
Posted by: Counsel | March 10, 2010 8:58 AM
I am surprised at the assertion that solar forcing has not changed during the 20th century. NASA has observed otherwise:
"Historical records of solar activity indicate that solar radiation has been increasing since the late 19th century." - that coincides with the end of the Little Ice age.
It was followed by a solar lull from about 1945 to about 1980, with marked global cooling causing concern about the onset of a new Ice Age. Then...
"Since the late 1970s, the amount of solar radiation the sun emits, during times of quiet sunspot activity, has increased by nearly .05 percent per decade..." - that coincides with the recent warming spell.
However, the past couple of years have been marked by record, devastating cold events around the world. Crop freezes, deaths of rare penguins due to extreme cold, coral bleaching off Florida due to prolonged cold, energy shortages as people try to stay warm. Again, NASA told us why:
"New measurements from a NASA satellite show a dramatic cooling in the upper atmosphere that correlates with the declining phase of the current solar cycle." - convective cooling as well as reduced solar energy reaching the ground cause a rapid response on land, even as oceans are very slow to respond.
Temperature has tracked changing solar output as we recovered from the Little Ice Age. The recovery began in the late 1800s and we are still not fully recovered to the Holocene temperatures that preceded the glacial advance.
Let's hope the current solar reduction does not last long. The effects could be catastrophic.
Posted by: Speak2Truth | March 9, 2011 12:24 PM