Winter is Coming

I was listening to the BBC radio the other day, and there was a discussion with a scientist about how the rising carbon dioxide level in the Earth’s atmosphere was driving global warming.  She compared the current mean level of over 400 parts per million to that during the last glacial period, of about 240 ppm, as a contributing factor towards the receding ice caps, and other global warming effects – one of several factors which also included orbital cycles, which could lead to glacial periods.  The interviewer asked whether this raised CO2 level was in effect preventing the onset of a new Ice Age.  Good question!  the scientist seemed to get quite uncomfortable at this point, almost appearing to laugh the question off.  Her answer was that we were not able to tell what the future would bring over these kinds of long time periods of 10s of thousands of years.

carbon_dioxide_levels

It’s interesting, isn’t it?  For quite some time, the scientific consensus is that human industrial activities are driving global warming, which is a BAD thing.  The apocalyptic consequences of this change over time is plainly spelt out by international organisations and leading scientists:

“The UN’s Intergovernmental Panel on Climate Change (IPCC) says that CO2 concentrations must be stabilised at 450ppm to have a fair chance of avoiding global warming above 2C, which could carry catastrophic consequences.” (1)

While I believe that bad things could indeed happen with rising global temperatures, I also think that insufficient consideration is being given to the alternative prospect.  We habitually speak of the ‘end of the last Ice Age’, but really it is not clear whether the 4 million year old Ice Epoch which we are at the tail end of has actually finished completely, or whether we are simply in the geophysical waiting room of the next glacial period/Ice Age.  The tumultuous changes bringing in these ice ages are cyclical, even routine.  For a large part, they depend upon astronomical cycles – the changing tilt of the Earth, procession, and the changing eccentricity of the Earth’s non-circular orbit – which were first linked to significant climate changes by Milutin Milankovitch in the 1920s.  With respect to these factors, we are currently moving back towards the ice, and have been for quite a while:

“The escape from Ice Age conditions, beginning 18,000 years ago, required the combined influence of all three astronomical to drag the Earth into a peak of warmth bout 6,000 years ago.  Orbital eccentricity changes combined with a shift in the wobble of the Earth which made June the month of closest approach to the Sun, boosting the heat of Northern Hemisphere summers, just at a time when the tilt of our planet reached a maximum, putting that summer Sun particularly high in the sky.  Since 6,000 years ago, all of these factors have turned around, and conditions for Northern Hemisphere summer warmth are becoming less favourable.  the prospect is for a return of Northern Hemisphere glaciation, on a timescale of thousands of years..” (2) 

Recent scientific work has illustrated how close we may be to this foreboding prospect, at least in terms of the changing nature of the Earth’s orbit around the Sun – one of the Milankovitch cycles.  At the moment, the northern summer as at its furthest point from the Sun, a factor which affects the amount of solar irradiation the Earth receives at the latitudes where sustainable glaciation would be triggered.  It has been proposed that the trigger point should have happened about 200 years ago, at the start of the industrial revolution, but that there is a fundamental relationship with atmospheric CO2 levels which must also be met (3).  As a result of the rising CO2 level, even at that point in history, the trigger point for Northern Hemisphere glaciation was missed:

“Under normal circumstances, the interglacial would be terminated, and a new ice age would start. So, in principle, we are in the perfect conditions from an astronomical point of view. If we had a CO2 concentration of 240 parts per million (200 years ago) then an ice age could start, but luckily we had a concentration that was higher, 280ppm.” (4)

Note the word ‘luckily’.  Suddenly, CO2 is our saviour.  If it hadn’t been for human activity, then, we might already be seeing ice caps extending southward in the Northern Hemisphere.  The conclusion drawn is that mounting CO2 levels are likely to offset a return to ice age conditions for a very considerable period of time:

“Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time.” (3)

There have been times when the threat of this kind of transition seemed only too real.  Another factor is the Sun’s own cycles, which directly affect the amount of warming irradiation the Earth receives.  One particularly cold patch in the 17th Century, during the ‘Little Ice Age’,  is a case in point.  It was at this point when the Sun reached the Maunder Minimum, a period of very low sunspot activity, culminating in the freezing over of major European rivers at the time.  But scientists don’t seem to have reached a consensus on the global importance of the Little Ice Age (5), or whether it even should be categorized in this way.  It is agreed, however, that from the 19th Century onwards, warming and glacial retreat have been the order of the day.

 

solar_system_ecliptic

Our understanding of the Sun’s complex cyclical nature is probably not yet as good as it might be.  There have been suggestions that we may face a new ‘Maunder Minimum’ in the 2030s (6).  This may be a factor offsetting the more general trend of global warming, leading to a temperature dip in the Northern Hemisphere.

So, it seems like we’re living on something of a climatic knife-edge.  There are multiple factors driving the Earth’s climate, and several of them point towards a future Ice Age, at some point.  Rising CO2 emissions seem to be pushing such a prospect further into the future than the regular glacial and interglacial cycles of the ‘current’ Ice Epoch suggest.

Which could be understood this way:  The global warming created by human industrial activity is actually preventing us from being plunged into an Ice Age, and perhaps we should be grateful for that.  This thinking is non-PC.  The problem here is that Science can sometimes behave like religion; creating dogmas and consensus opinions which individual scientists feel obliged to follow.  As I listened to the scientist on the radio squirm under the ‘common sense’ questioning, I reflected upon this:  With the media predator sniffing the air, the last thing the scientist wanted was to be separated from the herd.

 

Written by Andy Lloyd,  31st October 2016

References:

1)  Arthur Nelson “Carbon dioxide levels in atmosphere forecast to shatter milestone” 13th June 2016 https://www.theguardian.com/environment/2016/jun/13/carbon-dioxide-levels-in-atmosphere-forecast-to-shatter-milestone

2)  John and Mary Gribbin “Ice Age” pp88-9, Allen Lane 2001

3)  A. Ganopolski et al “Critical Insolation – CO2 relation for Diagnosing Past and Future Glacial Inception” January 2016,Nature 529(7585):200-203, http://www.nature.com/articles/nature16494.epdf

4)  Jonathan Amos “Carbon emissions ‘postpone ice age’” 13th January 2016 http://www.bbc.co.uk/news/science-environment-35307800

5)  John Rafferty & Stephen Jackson “Little Ice Age (LIA)” updated 18th March 2016 https://www.britannica.com/science/Little-Ice-Age

6)  Dan Hyde “Earth heading for ‘mini ice age’ within 15 years: Research has predicted a new solar ‘Maunder minimum’ in the 2030s” 11th July 2015,http://www.telegraph.co.uk/news/science/11733369/Earth-heading-for-mini-ice-age-within-15-years.html

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