what I couldn't understand with the historical temperature
reconstructions (based now in seems on tree ring growth) was the lack of
many of the features we know were present such as the warm period during
which Greenland was colonised.
For a while it seemed historians citing climate as a driver for events
were "exaggerating" to say the least.
The other point which worried me considerably when citing historical
climate was that the current 0.3C rise since the middle 20th century
hasn't had major impacts on our current civilisation, but the tree-ring
proxies seemed to show this as the biggest climatic change in the last
few thousand years.
Now the non-tree-ring proxies show much more variability in the past, of
an equal magnitude to the 20th century rise, it gives much more
credibility to historical accounts of climate affecting civilisations
because we now see that historical temperature variability was much
higher than appeared to be the case from tree-ring temperature proxies
Which in short really means it is OK again to cite climate as a driver
for historical events.
Beatrice Hopkinson wrote:
> Another aspect are micro-climate effects. Living in California we see
> this all the time- sometimes in rains in the front garden and not at the
> back - and vice-versa. A friend living at the coast where there was
> slippage and walked his dog every day along the cliff, found constant
> variations in plant life. I don't know enough about this subject , i,e.
> whether they are considering averages or areas, or latitudes, etc. etc.
> all of which should be taken into consideration.
> Beatrice Hopkinson
> Hon. Secretary Los Angeles Branch, Oxford University Society
> President, Droitwich Brine Springs and Archaeological Trust
> Board Member, Archaeological Institute of America
> Affilliate, Cotsen institute of Archaeology, UCLA
> [log in to unmask]
>> For anyone interested in historical temperature measurements the
>> following paper is a must read:
>> Because the very obvious different between temperature estimates based
>> on tree ring proxies and other proxies appear to throw into doubt any
>> historical temperature scale based on tree-ring proxies.
>> To put it in context, most tree-ring estimates of historical temperature
>> have a shape which barring the odd bit of noise appears to be completely
>> stable until the 20th century after which there is a sharp rise
>> (coinciding with the period of increased CO2 which is known to help
>> plant growth)
>> In contrast this temperature estimate using derived solely from proxies
>> which did not mainly use tree-rings shows the kind of temperature
>> changes historians recognise from accounts of the medieval warm period
>> and the little ice-age.
>> In explaining the difference the author suggests that whilst Trees do
>> respond to temperature and so tree rings do change with changes in
>> temperature, over a long period of time the forest itself will
>> self-adapt so that if periods encourage greater tree ring growth, more
>> trees will grow until the number reduces the rate of tree growth to the
>> long-term optimum for the species. Similarly, if climate changes to
>> reduce tree growth, forest's thin out so that individual trees then have
>> more chance of growing.
>> So the number of trees adapt to climate so as to tend to allow trees
>> always to grow at their optimum rate. SO ONLY IN PERIODS OF CHANGING
>> CLIMATE WHERE FOREST DENSITY HAS NOT HAD TIME TO ADAPT DO TREE RINGS
>> REFLECT ACTUAL TEMPERATURE CHANGE.
>> Obviously at the very least this throws into doubt any historical
>> temperature scale based on tree-ring proxies.