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OT: Moorabal/Lal Lal wind farm 10-Jun-2009 At 5:16:53 PM wombly

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Question for tony/rjames:

if you have studied:

> long term data (2,000 years up to 450,000 years) there's no evidence that our current climate trends
>are unusual. A lot of focus is put on the last 160 years for no good reason, other than that's the span
>of direct temperature measurement (sometimes called "recorded history". What specifically is
>unusual about our current climate that hasn't happened before many times?

you'll know that there's been some pretty big climate shifts during this period on a 100,000 year cycle -
it's the dominant story over the last million years or so, and has been found in so many places (ocean
temperatures, ice sheet changes, vegetation shifts, river lake expansions and contractions, the list
goes on). Milankovich (i.e. orbital) forcing on this timescale is pretty piddly when compared to these
changes - the main periodicity for those cycles is 40,000 years and 21,000 years. Changes in other
factors, such as albedo (i.e snow and ice reflecting more sunlight), or ocean currents are important
part of the story, but none of these are enough, even in concert. The answer is that you can only
explain these shifts by the effect of CO2 and other greenhouse gases.

And you should also know what is unusual about where we are going with respect to CO2
concentrations, and the likely climate that will follow. We haven't seen current atmospheric CO2
concentrations, and thus climate for at least a million years. i.e. for a period longer than our species
has been recognizable as us.