The Holocene PCC

Question 1) What does the Holocene ‘look like’ compared with glacial climate?

Greenland

The Holocene

about 1 K

The Holocene from a Greenland point of view Evidently, the Holocene at GISP2 is fundamentally different than the glacial period. Most people would attribute this to the huge “disruptions” in climate caused by things like “Heinrich events”, which case a great deal of difference from one millennium to the next (but which don’t occur during the Holocene) But how much does the rest of the world (outside Greenland) care about whether it is “glacial” or “Holocene” conditions?

Millennial-scale change

Cariaco Basin What accounts For the Holocene variability at Cariaco basin? Doesn’t the variability appear just as large on millennial timescales as it is during the glacial? Many many other records look just like this. So… what is the cause of millennial scale variability during the Holocene?

Santa Barbara: Bioturbation

Point 1. The Holocene isn’t necessarily less variable than glacial climate. Many (most) records suggest as much millennial-scale variabilty during either time period.

Question 2 What does millennial scale variability mean, anyway?

Example: Random “climate proxy” data, annually averaged.

Example: The same “climate proxy” data, millennially- averaged. Note the “significant millennial- scale variability”!

Example: Annually averaged and millennially averaged data on the same vertical scale. Oops, the “millennial-scale variability” is not so important after all, is it?

GISP2 Calcium Calcium is a proxy for “dustiness” Red shows 1000-year averages, blue = 20-yr averages. Note that the “millennial-scale” variabilty is nearly as great as the 20- year variability. Yes, the data really are at <20yr resolution throughout.

GISP2 Calcium -- the Holocene On the other hand, during the Holocene, the 20- year variabilty is far greater than the 1000-year variability.

“Variability” Point 2: The only sensible definition of “millennial-scale” variability is the magnitude of variability in millennially-averaged climate data”. This is important because all climate or climate proxy data will display some variability from millennium-to-millennium. The question is whether it is important.

Question 3. Okay, with the caveat about magnitude, what does millennial-scale variability look like during the Holocene, globally?

A popular cartoon version of Holocene variability

Point 3. There is a strongly held view that millennial-scale fluctuations During the Holocene have a discernible global pattern (in phase, or out of phase), and can be linked to solar variablity. But the data are rather a mess…leading to Question 4) What do the glacier records show?

Lateral moraines, Bylot Island, Canada

Greenland ice sheet margin

Point 4. The evidence seems rather good that there is nothing coherent happening during the Holocene. Balco writes: The answer to the question "were Holocene glacier Advances in the Northern and Southern Hemispheres in phase, or out of phase?" turns out to be "no."

Question 5. So do you mean it’s all noise? No ‘cause’? No solar variability or thermohaline circulation changes needed? Maybe, maybe not..

A bit of history (much of what we think we know about the last 2000 years of climate is prejudiced by our European historical knowledge and evidence of glacier advances in Europe and North America (hence the term “little ice age”)

The Holocene about 1 K

1850 A.D. Little Ice Age Medieval Warm Period

The Holocene about 1 K It is often said that <the ‘Little Ice age” was merely the largest And most recent of the Holocene “millennial-scale” fluctuations>

Point 5. We probably ought to understand the most recent ~2000 years better than we do now.

A last point about the Holocene: Evidence is good that the long term changes in Holocene climate are the direct response Milankovich forcing

End

Taylor Dome Borehole Temperatures “Little ice age” “Medieval warm period”