The coming zero snow depth season #1

One of a series; also see editions: #2, #3, #4

I guess lots of people hear global warming predictions of a couple of degrees increase and think, so what?  Take a close look at the snow depth prediction equation.  The factor on southern sea surface temperature¹ (SST) is -130.  That’s right, a 1°C increase in southern ocean temperature decreases our season peak, high-altitude snow depth² by 130 cm.

But it’s not quite that simple.  Multiple regression factors reflect the whole suite of parameters (we have six), not just the particular one.  Here’s what the relationship looks like if we just focus on SST:




The factor falls from 130 to 82.  But how much of that is causative?  We know that southern SST has been rising at the same time as peak snow depth has been falling.  Maybe this is just correlation, without any mechanism directly connecting the two (like, say, hot water -> less snow).  Here’s what we get if we take the trends out of both, and just look at the year-to-year variations:




Whoops, the factor goes right back up to 124.  On a year-to-year basis, warmer SSTs really do seem to mean less snow.

I don’t know what the exact factor should be, but it’s pretty clear to me that there’s a real effect here, and that it’s probably directly causative.  If the right factor was somewhere in the middle, say 100, that would mean for every 1°C rise in southern sea surface temperature the peak snow depth would fall by 100 cm.  As of 2014, our average peak depth is down to just 177 cm.  Lose 1 m and the Australian snow season is practically gone, lose 2 m and it definitely is.

I don’t know how to make this clearer.  Another 2°C increase and our snow season is history.

Southern sea surface temperature in our area of interest has been rising at about the same rate as global average warming³ : +0.6°C since the mid 1950s compared with +0.65° globally.  So when next you hear that global warming will be x°C by whenever, just remember, multiply by 100.


How soon will we see our first ever zero snow depth season?  I’m working on an estimate; it may be sooner than you think.



1. Sea surface temperature in the Great Australian Bight and northwest Tasman Sea averaged over latitude 30-37°S, longitude 115-160°E.

2.  At ~1830 m elevation at Spencers Creek near Charlotte Pass, Australia, midway between Perisher Valley and Thredbo; data courtesy Snowy Hydro Limited.

3. Worldwide average sea surface temperature is rising more slowly than the global average warming rate (because the land warms faster), but the polar oceans are warming faster than average due to polar amplification.  The effects appear to roughly cancel for our area.

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