L2

Question 1

Define Climate sensitivity

Answer 1

Change in climate (temperature) for a given forcing

Question 2

What is natural variability

Answer 2

Natural changes in climate such as El nino which change the climate naturally

Question 3

What is the Ruddiman hypothesis

Answer 3

The theory that anthropogenic climate change did not start in the 18th century but 8000 years ago beginning with intensive farming, because this is the time greenhouse gases stopped following their natural patterns

Question 4

when was the first global themometer measurments taken

Answer 4

1850

Question 5

what is a climate proxy

Answer 5

1. A recorded quantity from which some aspect of the climate at a particular time in history can be inferred.

Question 6

what is the advantage of a climate proxy

Answer 6

very long record ( potentially millions of years)

Question 7

what are the disadvangages of climate proxies

Answer 7

• responds to several climate variables in a complex way
• limited resolution ( space and time)
• must be preserved (record may be biased or overprinted)

Question 8

what do wide and narrow rings in tree rings mean

Answer 8

wide ring = warm days and sufficient water

narrow ring = stressful conditions eg water shortages

Question 9

what properties of a tree ring can be measured

Answer 9

width
density of early wood
density and width of wood grown late in season
isotope chemistry of wood –> teaches us composition of rainfall and the rate of photosynthesis

Question 10

what is the oldest trees ever measured (dead)

Answer 10

50,000 years ago, chilean trees covered in mud that was then uncovered in an earthquake in 1960AD

Question 11

What are the oldest living trees cored

Answer 11

9000 year old californian bristlecone pines

Question 12

what is an isotope

Answer 12

a chemically identical form of an element with different atomic mass

Question 13

how do we use oxygen isotopes

Answer 13

16 O is preferabbly evaporated meaning more 18 is left behind. 18 is preferentially rained out.
hotter
when temps are colder there is less 18O in ice sheets and more in the oceans

Question 14

how are calcium carbonate shells and oxygen isotopes linked

Answer 14

the amount of 18o in shells can be measured to link the temperature (similar to a ice core)

Question 15

what are the differences between antarctic and greenland ice core

Answer 15

antarctic ice cores have a large sense of time, greenland ice cores have a much higher resolution

Question 16

what are written records like

Answer 16

go back 1000 years
quite unreliable
more about amounts of harvest etc

Question 17

what was the little ice age

Answer 17

cold period in the 16th century

Question 18

when was the little iceage

Answer 18

from 1550 for about 150 years

Question 19

what and when was the medival warm period

Answer 19

warming from 600 ad to 1250 AD

Question 20

Name four proxies or other ways in which we can reconstruct the climate before instrumental measurements.

Answer 20

Examples covered in the lecture included: tree ring width, oxygen isotopes, written records, pollen records in bogs, cave deposits, etc. There are others!

Question 21

What are the difficulties of using tree rings to reconstruct climate?

Answer 21

3. Tree rings respond to several different environmental factors (e.g. water availability, light, temperature, disease), which may vary with location and may not directly link to the variable being reconstructed, so it can be difficult to infer that variable (e.g. temperatures) from the width of the ring.

Question 22

Roughly how far back in time can tree rings be used to reconstruct the climate?

Answer 22

Some studies have managed to go back to the last ice age, over 12 thousand years ago (ka) in a continuous record by connecting tree ring records of living and dead trees. The oldest trees in the world are ~ 9 thousand years old. There are studies of 50 thousand years ago (but these don’t extend to present).

Question 23

Where can we find a record of oxygen isotope abundance to reconstruct climate, and how far back does it go?

Answer 23

In ice cores or in lake and marine sediments. Ice cores records have high temporal resolution and can go back several hundred thousand years (~800 thousand years max with EPICA Dome C ice core in Antarctica, Greenland is much less). Sediment cores can go back tens of millions of years, but the temporal resolution is often quite low because they are controlled by sedimentation rates.

Question 24

Explain what enables oxygen isotopes to be used for climate reconstruction.

Answer 24

Oxygen in water (H2O) can be either abundant 16O (“normal” oxygen) or less abundant 18O (heavy oxygen). Water containing the heavier 18O is not evaporated as easily as 16O, and condenses to form clouds and rain more easily than 16O. At lower temperatures this effect is enhanced. So when temperatures are low, the 18O becomes depleted in high latitude ice caps because it is both depleted during evaporation at lower latitudes and then preferentially rained out from the atmosphere as the air is transported to the pole (i.e. before it reaches the ice cap). The signal is archived in ice (There is a similar record in cave deposits; speleothems).
Because the oxygen isotopes that falls as snow over ice is then locked away in the ice until it melts, the 18O:16O ratio of global seawater changes when the size of the ice sheets change. So 18O in seawater also records the global ice volume. Generally, 18O of global seawater is higher (enriched) when there is more terrestrial ice because snowfall over the polar ice caps is depleted in 18O (i.e. locking away relatively more 16O in the ice, and leaving more 18O for the oceans).
Calcifying marine biota form their shells from the seawater around them. Chemical fractionation of oxygen occurs during this process. When temperatures are cooler, the organisms enrich their shells in 18O (so 18O is higher). When temperatures are warmed, the shells are depleted in 18O (so 18O is lower).
So, how 18O records temperature change depends on the archive you are measuring (e.g. ice core versus fossilised marine biota)!

Question 25

What is the Central England Temperature, how was it obtained, and over what period?

Answer 25

The CET is a reconstructed climate record for a region of central England based on written records. It goes back to about 900 CE, although more robust quantitative measurements only go back to 1659.

Question 26

What is a climate anomaly?

Answer 26

An anomaly is a period of climate that is significantly different from the long-term average.

Question 27

What is the Medieval Climate Anomaly (MCA)?

Answer 27

The MCA was a transient anomalously warm period of several hundred years from about 1100 to 1300 CE.

Question 28

Did the MCA occur over the whole world?

Answer 28

No, the MCA was restricted to parts of the northern hemisphere; i.e. it was not hemispherically synchronous.