On Wed, Nov 26, 2008 at 10:38:42AM +1100, Graham Turner wrote:
> How do you reach this conclusion? My understanding is that there have
> been long slow changes in climate since the industrial revolution and the
> increasing use of fossil fuels for industry etc.
Not really. Attribution studies estimate neglible impact on climate
from increases in greenhouse gases before 1910 and only a small impact
until the 1960s. Until the 1960s cooling from anthropogenic aerosols
probably balanced or exceeded the warming from anthropogenic greenhouse
gases and natural factors such volcanic aerosols and solar variations
were of similar magnitude to both during this period. Land use changes
such as clearing for agriculture might have has a significant impact on
climate stretching back further - but I gather this isn't well understood.
In any case if you look at climatic records for NSW, e.g. here
http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/timeseries.cgi?variable=tmean®ion=seaus&season=0112
mean temperatures were falling for significant parts of the Figbird
invasion. Figbirds could be responding to another climate variable but,
as Lawrie says, other human environmental changes are more plausible
explanations.
There may well be other birds than frugivores expanding South, e.g
Bar-shouldered Dove, and there are of course expansions from other
directions into coastal NSW like Crested Pigeon and White-plumed HE.
I'm not sure Brahminy Kite have expanded south - there is a Watling (pre-1800)
drawing of a Brahminy Kite, so their pre-European range might have included
Sydney, although it conceivably could have come from a bit further north.
> I have never argued anywhere about 'proof' of climate change, in fact I
> regularly ask the 'true believers' for such proof. I am still waiting to
> see any measurable rise in sea level.
We have been measuring a ~3mm/year rise in sea by satellite since the
early 1990s. This GRL paper summarizes the more difficult task
of estimating sea level rises for 3 centuries before that
http://www.ulapland.fi/home/hkunta/jmoore/pdfs/Jev2008GL033611.pdf
Michael Norris asks about Grey Nurse Sharks in Port Philip Bay. They are
circumglobal and must have previously occurred in Port Philip Bay and
presumably would again if their numbers ever recover.
Andrew
|
