The Holocene

PCC 589

2009

Question 1)

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

-45

-43

-41

-39

-37

-35

-33

020000400006000080000100000

Age (years before present)

del18O

Greenland

The Holocene

-37

-36

-35

-34

-33

-32

0200040006000800010000

Age (years before present)

del18O

The Holocene

-37

-36

-35

-34

-33

-32

0200040006000800010000

Age (years before present)

del18Oabout1 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

-62

-60

-58

-56

-54

-52

-50

0 50 100 150 200Age (thousands of years before present)

δ18 (‰)O

Vostok

Cariaco BasinWhat accountsFor 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 fluctuationsDuring the Holocene have a discernible global pattern(in phase, or out of phase), and can be linked to solarvariablity.

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 nothingcoherent happening during the Holocene.

Balco writes:

The answer to the question "were Holocene glacierAdvances in the Northern and Southern Hemispheresin 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 circulationchanges needed?

Maybe, maybe not..

A bit of history

(much of what we think we know aboutthe last 2000 years of climate isprejudiced by our European historicalknowledge and evidence of glacier advances in Europe and North America (hencethe term “little ice age”)

The Holocene

-37

-36

-35

-34

-33

-32

0200040006000800010000

Age (years before present)

del18Oabout1 K

-36

-35.5

-35

-34.5

-34

05001000

Age (years before present)

del18O

1850 A.D.

Little Ice Age

Medieval Warm Period

The Holocene

-37

-36

-35

-34

-33

-32

0200040006000800010000

Age (years before present)

del18Oabout1 K

It is often said that <the ‘Little Ice age” was merely the largestAnd 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 changesin Holocene climate are the direct response Milankovichforcing

End

-46

-44

-42

-40

-38

0 0.5 1 1.5 2Age (thousands of years)

Te

mp

era

ture

(C

)Taylor Dome Borehole Temperatures

“Little ice age”

“Medieval warm period”