"The scheduled service to the 'Next Ice Age' is delayed..."

There is change afoot at Earth station central, where humankind appear to be rewriting the timetables. Trouble is, this could be inviting unforeseen circumstances further down the line...

Imagine one morning, you wake up (or rather, you don't), buried under 10 feet of snow. You desperately fight your way to a window, a gap in the snow, anything which allows you to look outside. Searching for a familiar landscape of rolling green hills and townscape, instead you find a barren, desolate, ice-covered horizon. Am I dreaming, you think? What has happened to planet Earth as we know it?

The Ice Age which never arrived - artificial scenes from The Day After Tomorrow (Source)

Well, this (slightly dramatic) scenario could have been a cold, hard truth for humanity over the next millennium, though not taking place on the overnight time-frame as suggested in films like The Day After Tomorrow. Ever since humans started inadvertently tampering with the CO2 dial in the atmosphere, Earth's future path has veered somewhat off-piste. Before copious layers were sewn to a seemingly ever-growing blanket of greenhouse gases in the atmosphere, it is believed the planet was en route to a new ice age. Now, however, this glaciation isn't likely to happen any time into the foreseeable future, and it's because of humans.

Research led by Chronis Tzedakis, a professor at UCL, has suggested that the onset of a new ice age would begin in 1,500 years time, IF (and this is a very important 'if') CO2 concentration were still at pre-industrial level (~280 parts per million (ppm)). Since the dawn of human civilisation, increased agriculture, the industrial revolution, and the most recent Great Acceleration period (see my last post), CO2 has risen to an average today of almost 400ppm, nearly double the threshold of ~240ppm required for glaciation! Even if anthropogenic emissions were shut down tomorrow, it would take a considerable amount of time to bring atmospheric CO2 concentrations down enough to support a big freeze.

Interglacial-glacial cycles are largely controlled by the slow, cyclical changes in the nature of Earth's orbit around the Sun. These are called Milankovitch cycles, and take place on timescales of tens of thousands of years. A key trigger for ice age inception is weak insolation (low heat from the Sun) during the summer months. Tzedakis et al (2012) compared present day to an interglacial 780,000 years ago, Marine Isotope Stage (MIS) 19c. Both time periods have similarities in orbital configuration regarding weak summer insolation. The difference is that CO2 is much higher today, and this is overpowering the orbital forces which should be driving present-day glaciation.

Milankovitch Cycles of eccentricity, obliquity, and precession (Source)

Though ice ages are ultimately forced by orbital changes, internal climate feedbacks are also vital. When summer solar radiation is low, snow and ice that fell in the previous winter are preserved at high latitudes year-round, and thus are added to the following winter. With this pattern repeating annually for hundreds and thousands of years, Earth starts embarking on a slippery slope to a new ice age. An important impact of increased snow and ice is that an albedo positive feedback loop is created, as light-coloured snow/ice reflects more heat than darker-coloured land, cooling things down just that bit more (see diagram below).

Albedo is greater with snow/ice covered land surface, which means more heat is reflected, thus more snow/ice stays, which reflects more heat etc. A positive feedback loop is formed which has a cooling effect (Source)

Postponing a new ice age might seem like cause for celebration (I'm looking at you, you sun-worshipping, beach-loving, tanned folk). But consider this. Humanity's modification of the atmosphere through anthropogenic carbon dioxide emissions is enough of a planetary-scale forcing to seriously delay the onset of what would've been a natural ice age in Earth's life cycle. The increased albedo needed to shift Earth into a new glacial state cannot and will not happen whilst humans are a dominant geological force. We're tampering with a very sensitive climate system, approaching terra incognita, accompanied by some serious unprecedented consequences. 

Regardless of when human influence of this type upon the planet begun (8000, 200, or 65 years ago), it can be considered unnatural and unhealthy, as it is preventing Earth from undergoing normal cyclical changes. If there's any evidence needed to show that humanity's impact is planetary-scale and significant enough to warrant recognition of the Anthropocene, this is it. This time, it won't be leaves on the line that delays our arrival at the next station 'Ice Age', but something much bigger...

Tzedakis et al's paper is really worth a read, but is perhaps a little heavy reading for those of you unfamiliar with paleoclimatology. Instead, check out Andrew Revkin's 'dotearth' blog post, which nicely summarises the paper and contains some interesting responses from other scientists regarding the findings!