Ice Age not for 60 thousand years – if ever
Thanks to my sister, I have been doing some catching up on a TV series currently showing in the UK called Orbit: Earth’s Extraordinary Journey. Although derided by some TV commentators…
Stuart Jeffries in The Guardian (on 4 March 2012)
Andrew Anthony in The Observer (on 11 March 2012)
…I agree with my sister, it has been very good.
The second episode was particularly so (IMHO): Following in the footsteps (at times literally) of Sir David Attenborough (Frozen Planet) and Professor Brian Cox (Wonders of the Universe), co-presenters Kate Humble and Dr Helen Czerski went to extra-ordinary lengths and amazing locations to explain the vagaries of the Earth’s climate past, present, and future.
For example, whereas I have previously got myself in a terrible mess trying to explain the causes of Ice Ages (as indeed it is at least arguable that James Hansen did in Storms of my Grandchildren), Humble and Czerski accomplish this with ease (and the help of some excellent computerised animation). For those of you without access to the BBC’s iPlayer; and/or those that cannot wait for the programme to be broadcast in your home country (as I am sure it will be eventually), I will try and summarise the three aspects to the Earth’s orbit around the Sun that contribute towards the occurrence of Ice Ages:
1. The date on which the Earth comes closest to the Sun during its elliptical orbit (i.e. Perihelion).
2. The extent to which the Earth’s orbit deviates from near-circularity (i.e. eccentricity).
3. The angle at which the Earth’s axis of rotation is tilted from vertical (i.e. perpendicular to the plane around the Sun in which its orbit lies).
All of these things are caused by gravitational interaction between all the planets in our solar system and the Sun itself; they are all therefore highly predictable even if not all regular and, therefore, once we understand these changes, we can trace their effects back through time. We can of course also calculate their effects today.
For example, perihelion currently occurs on January the third each year, whereupon the Earth is 5 million miles closer to the Sun than it is in July; which equates to 7% more energy input from the Sun. However, any effect this might have is more than cancelled out by the 23 degree tilt of the Earth’s axis of rotation away from the Sun causing a 50% reduction of insolar radiation to the northern hemisphere in winter.
Meanwhile, despite receiving 7% more insolar radiation from the Sun, summers in the southern hemisphere are on average 4 Celsius cooler than those on the northern hemisphere!!! Indeed, if you go 55 degrees south of the equator (e.g. southern Chile) you will find glaciers not seen in the English Lake District for several millennia. The reason for this discrepancy turns out to be the presence of the Great Southern Ocean… Whereas the seas surrounding the UK have a moderating influence on climate (avoiding the temperature extremes of Eastern Europe and Russia), the general absence of land in the southern hemisphere (which warms up faster than the oceans) has on overall cooling effect on climate.
It turns out that heat capacity is fundamentally important. Although the oceans are slower to respond to energy input (i.e. they have a higher heat capacity), the land also takes time to gain and to lose heat. This is the reason why the coldest day of the year in the northern hemisphere is often on or around the 19th of January; but why ice road truckers can continue to drive across frozen lakes in northwest of Canada well into March.
So, to get back to Ice Ages, I really don’t understand how we ever thought we were heading for one, or why some people still say we might be heading for one. This is because, in order for an Ice Age to occur, all three of the above-mentioned cycles must coincide to cause cooler summers in the northern hemisphere where most of the land is and therefore where most ice can develop and not melt (in order for glacier formation to begin). At the moment, perihelion is the only factor promoting this; and it will not coincide with extreme eccentricity and minimum angle of tilt for another 60 thousand years.
Meanwhile, we just have a slight problem of anthropogenic climate disruption to deal with.
If you remain unconvinced, please watch this brilliant 7-minute video produced by the Pacific Institute for Climate Solutions (and remember even if we stopped burning fossil fuels tomorrow, CO2 rise [and therefore warming] would continue for decades)…