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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.
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.
