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A Review of Temperature Reconstructions

Jack Hays

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This is an interesting review. Both warmists and skeptics will find something to champion. Data is like that.


A review of temperature reconstructions

Guest essay by Andy May In previous posts (here and here), I’ve compared historical events to the Alley and Kobashi GISP2 Central Greenland Temperature reconstructions for the past 4,000 years. Unfortunately, these two reconstructions are very different. Recently Steve McIntyre has suggested a third reconstruction by Bo Vinther. Vinther’s data can be found here. Unfortunately,…
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Conclusions
. . . The use of temperature proxies to determine surface air temperatures prior to the instrument era is very important. This is the only way to determine natural long term climate cycles. Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made. Yet, these shorter cycles are clearly not the only cycles. When we look at longer temperature reconstructions we see 100,000 year glacial periods interrupted by brief 20,000 year interglacial periods. These longer periods will probably only be fully understood with more accurate reconstructions. Intermediate ~1500 year cycles, called “Bond events” have also been identified.
Tree ring proxies older than 500 years and younger than 100 years are anomalous. This anomaly is large enough to cast doubt on any temperature reconstruction that uses tree rings. Between lake and marine sediment proxies and ice core proxies it is harder to tell which is more likely to be closer to the truth. They agree well enough to be within expected error. All of the proxies diverge from the mean with age, none appear to be very accurate (or more precisely in good agreement) prior to 1100 AD. It does appear that all of the proxies except the tree ring proxies, could be used for analytical work back to 1100 AD; this is encouraging.
The other very important use for temperature reconstructions is to study the impact of climate changes on man and the Earth at large. Historical events are often known to the day and hour, only when we have reconstructions with more accurate time scales can we properly match them to major events in history. In addition, this work made it clear that combining multiple proxies causes severe dampening of the temperature response because the time scale error causes peaks and valleys in the average record to be reduced. Multiple proxy reconstructions show less temperature variation than actually occurred. Ideally, we need a very accurate time scale on all proxies so they can be combined properly. But, achieving more accuracy than 50-100 years will be difficult given current dating technology. Tree rings are more accurate than this, but they are a poor indicator of temperature. There is a lot of work needed in this area.



 

Befuddled Alien

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This is an interesting review. Both warmists and skeptics will find something to champion. Data is like that.


A review of temperature reconstructions

Guest essay by Andy May In previous posts (here and here), I’ve compared historical events to the Alley and Kobashi GISP2 Central Greenland Temperature reconstructions for the past 4,000 years. Unfortunately, these two reconstructions are very different. Recently Steve McIntyre has suggested a third reconstruction by Bo Vinther. Vinther’s data can be found here. Unfortunately,…
Continue reading →

Conclusions
. . . The use of temperature proxies to determine surface air temperatures prior to the instrument era is very important. This is the only way to determine natural long term climate cycles. Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made. Yet, these shorter cycles are clearly not the only cycles. When we look at longer temperature reconstructions we see 100,000 year glacial periods interrupted by brief 20,000 year interglacial periods. These longer periods will probably only be fully understood with more accurate reconstructions. Intermediate ~1500 year cycles, called “Bond events” have also been identified.
Tree ring proxies older than 500 years and younger than 100 years are anomalous. This anomaly is large enough to cast doubt on any temperature reconstruction that uses tree rings. Between lake and marine sediment proxies and ice core proxies it is harder to tell which is more likely to be closer to the truth. They agree well enough to be within expected error. All of the proxies diverge from the mean with age, none appear to be very accurate (or more precisely in good agreement) prior to 1100 AD. It does appear that all of the proxies except the tree ring proxies, could be used for analytical work back to 1100 AD; this is encouraging.
The other very important use for temperature reconstructions is to study the impact of climate changes on man and the Earth at large. Historical events are often known to the day and hour, only when we have reconstructions with more accurate time scales can we properly match them to major events in history. In addition, this work made it clear that combining multiple proxies causes severe dampening of the temperature response because the time scale error causes peaks and valleys in the average record to be reduced. Multiple proxy reconstructions show less temperature variation than actually occurred. Ideally, we need a very accurate time scale on all proxies so they can be combined properly. But, achieving more accuracy than 50-100 years will be difficult given current dating technology. Tree rings are more accurate than this, but they are a poor indicator of temperature. There is a lot of work needed in this area.




k ... so what do YOU think about this?? (It seems weird to just post a wall of text and plead people to look at it but I am new here and may not be aware of the norms)
 

Jack Hays

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k ... so what do YOU think about this?? (It seems weird to just post a wall of text and plead people to look at it but I am new here and may not be aware of the norms)

I think there are enough unknowns that anyone who claims any single reconstruction "proves" anything is foolish. The only thing I think is clear is that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.
 
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Befuddled Alien

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I think there are enough unknowns that anyone who claims any single reconstruction "proves" anything is foolish.


I agree. Proofs are for maths and formal logic. Science, not so much.

The only thing I think is clear is that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.

How does this conclusion follow from what you posted?
 

Mithrae

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k ... so what do YOU think about this?? (It seems weird to just post a wall of text and plead people to look at it but I am new here and may not be aware of the norms)

Most people who've been here for a while are just relieved when Jack's C&Ps are given a new thread, instead of being inserted randomly into other topics. But in fairness, they do sometimes contain interesting information, or at least entertainingly false notions.


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A review of temperature reconstructions

Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.

'Recent' is a pretty obvious weasel word there. Over the period 1970 to 2010? Maybe, though doubtful even then.

In the longer term though, the thing about oscillations - the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation and most obviously the shorter El-Nino Southern Oscillation - is that they oscillate. In periods of a century or more all of these oscillations individually or combined have a net effect of roughly zero.

Wood for Trees
trend
 

Jack Hays

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I agree. Proofs are for maths and formal logic. Science, not so much.



How does this conclusion follow from what you posted?

As stated in the conclusions section:

Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.
 

Jack Hays

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Most people who've been here for a while are just relieved when Jack's C&Ps are given a new thread, instead of being inserted randomly into other topics. But in fairness, they do sometimes contain interesting information, or at least entertainingly false notions.

They only seem random to those who lack the imagination to see the connections.
 

Jack Hays

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Most people who've been here for a while are just relieved when Jack's C&Ps are given a new thread, instead of being inserted randomly into other topics. But in fairness, they do sometimes contain interesting information, or at least entertainingly false notions.


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#####




'Recent' is a pretty obvious weasel word there. Over the period 1970 to 2010? Maybe, though doubtful even then.

In the longer term though, the thing about oscillations - the Pacific Decadal Oscillation, the Atlantic Multidecadal Oscillation and most obviously the shorter El-Nino Southern Oscillation - is that they oscillate. In periods of a century or more all of these oscillations individually or combined have a net effect of roughly zero.

Wood for Trees
trend

Do you realize you reinforced the author's point?
 

Jack Hays

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I'm sure you imagine so.

His point is that the natural oscillation you accurately identify is in fact responsible for a good deal of observed "warming."

Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.
 

Mithrae

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His point is that the natural oscillation you accurately identify is in fact responsible for a good deal of observed "warming."

Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made.

And the thing about oscillations is that they oscillate: Over a century or more their net effect is close to zero. In a carefully selected time-frame (say 1970 to 2010) the PDO and AMO undoubtedly contributed significantly to the observed warming, though probably not half. But over the whole course of the instrumental record, their contribution to the ~0.8°C of warming has been minimal.


Edit: Using a 1 year (13 month) mean more clearly shows the influence of the AMO especially on temperature cycles; but just as obviously shows that it is a modulating effect only which can't explain the long term warming trend:

Wood for Trees
mean:13



Edit 2: And in fact on second glance many of those AMO changes seem to follow the global temperature changes, so I'm not even sure about that modulation.
 
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Jack Hays

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And the thing about oscillations is that they oscillate: Over a century or more their net effect is close to zero. In a carefully selected time-frame (say 1970 to 2010) the PDO and AMO undoubtedly contributed significantly to the observed warming, though probably not half. But over the whole course of the instrumental record, their contribution to the ~0.8°C of warming has been minimal.


Edit: Using a 1 year (13 month) mean more clearly shows the influence of the AMO especially on temperature cycles; but just as obviously shows that it is a modulating effect only which can't explain the long term warming trend:

Wood for Trees
mean:13



Edit 2: And in fact on second glance many of those AMO changes seem to follow the global temperature changes, so I'm not even sure about that modulation.

And that is the author's point: over the time scale of recent observed warming, about half is attributable to oscillating phenomena.
 
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