DID you know that over the last 450,000 years there have been four ice ages lasting around 100,000 years each? And five interglacial periods lasting around 12,000 years each? Look at this graph of temperature data derived from the Vostok ice core from Antarctica.
What it means is that for around 90 per cent of the last 450,000 years Earth has been in ice age, where global temperatures have slumped to as low as 10 deg C colder than in the relatively brief interglacial periods. The current interglacial period (the fifth) began about 11,600 years ago, suggesting it may not last much longer. It corresponds to the time when human beings began farming and building cities and civilisations.
It is notably cooler than the previous four interglacial periods. If we ‘zoom in’ on it (see the upper graph, below)
we can see that it has been getting progressively cooler for the last 3,500 years, ‘presumably indicating the early stages of the coming ice age,’ says climate scientist Ole Humlum. https://www.mn.uio.no/geo/personer/vit/geohyd/olehum/index.html
We also see that it is punctuated by periods warmer than the rest, most recently the Minoan warm period, the Roman warm period and the medieval warm period. The current warm period after the ‘Little Ice Age’ of 1300-1850 (not shown as the graph ends in 1854), which according to Humlum has currently reached around the same temperature as the medieval warm period, may well be part of this natural pattern rather than driven by carbon dioxide emissions. The lower graph shows CO2 concentration over the current interglacial period, and there is no obvious relationship with temperature. Over a longer period CO2 is seen to lag temperature by several thousand years rather than lead it, suggesting higher temperatures may drive greater CO2 concentrations rather than vice versa. https://wattsupwiththat.com/2014/12/27/vostok-and-the-8000-year-time-lag/
However, it is true that in the past 150 years CO2 concentrations have rocketed from around 280ppm to 395ppm, a level unprecedented in the past 12,000 years. Furthermore, since the end of the upper graph (in 1854) the temperature has risen to around the same balmy levels last seen in the Middle Ages. (This is assuming that the recent temperature data has not been misleadingly adjusted, as some believe to be the case.)
This in itself is not alarming – the reported temperature rise is hardly unprecedented in the current interglacial period, and warmer temperatures (and higher carbon dioxide concentrations) provide better conditions for life to flourish. However, if it is the case that current levels of carbon dioxide are driving runaway warming, that would obviously be deeply concerning. That is the question current climate science is sharply focused on, though more often than not with only one acceptable answer, it seems.
Since the cost of cutting carbon dioxide emissions is huge, and will negatively affect the environment in other ways, it is well worth being sure that this is the case before taking any significant action to reduce emissions. Despite much alarmism about a present climate emergency, time does seem to be on our side. While temperatures appear to have been rising on and off over the last century by about 0.15 deg C per decade, they did fall in the 1960s and 70s, and paused between 1998 and 2013, suggesting a degree of natural variability.
If temperatures continue to rise and eventually reach levels unprecedented in this (or any recent) interglacial period then we’ll know there’s something to consider taking concerted action about, as there may be a risk that human emissions have initiated a positive feedback loop resulting in unsustainable temperature rises. Though what counts as unsustainable is also an open question, as on a longer geological timescale we are currently in an extended ‘ice house’ age of around 30million years, whereas for 91 per cent of the last 550million years the Earth had no permanent ice caps at the poles at all. From this perspective, how warm is too warm?
On the other hand, if we find temperatures stabilising for a while, oscillating a bit, maybe falling again, then we can be more confident that we have not left the natural cycles.
Whether that is itself a good thing is a matter for debate. In the 1970s scientists were warning about the onset of a new ice age, when Iceland was blocked with ice and ‘climate change’ meant global cooling. That turned out to be a false alarm, but the reasoning wasn’t entirely unsound. The present interglacial period, if history is any guide, may have just about run its course. And what then? Human civilisation has appeared and endured only during the present interglacial warmth. How will more than 8billion people cope with the much harsher conditions of a climate chilled by 6-8 deg C, one much less conducive to life, abundance and comfort?
Let us watch and wait for now, then, and see how things look in 2030. In the meantime, we shouldn’t take the present warmth for granted. We’ll miss it when it’s gone.