Happy Holocene

It is claimed that we are experiencing some sort of unique warming climate event which can not be explained as a natural climate variation and therefore human beings must be causing it. Obviously a big part of proving such a proposition would be to compare todays climate to what we know about the climate in the past. Usually climate alarmists will make comparisons of today’s temperatures to the climate of the last 1000 years. This arbitrary date is only selected for presentational purposes because by limiting the comparison to that short period the temperature today can be made to look, by tweaking of the evidence, odd and anomalous. I want to roll the clock back a bit further to the period between 10,000 and 5000 years ago and also locate that period in the broader context of the climate going back much further.

Nothing in this description of climate history is disputed by any scientist or climatologist.

The current phase of climate that we are living in now only started about 10,000 years ago. The general pattern of climate for the last several million years has been that of long periods of much colder climate called ice ages which were also periods of much greater climate variability. During a typical ice age period (which usually lasted for more than a 100,000 years) the temperatures were always much lower than during the last 10,000 years but there were also huge upward and downward shifts in temperature, shifts that were much, much bigger than anything we have seen in the the last 10,000 years.

Its is worth noting that during the last ice age, whilst it was much colder and the climate was shifting constantly, modern humans left Africa and successfully colonised the planet using only stone tool technology. The huge and endless shifts in climate during this period would have made the development of agriculture impossible as habitats would have been constantly shifting.

Between the various ice ages, each lasting more than 100,000 years, there have been very short periods of a few thousand years when the climate was much warmer. These are called Interglacials.

We live in such a period. It is called the Holocene.

The Holocene, although broadly typical of other interglacials is marked by the following characteristics:

It has gone on a bit longer than previous interglacials

Its temperature has been a bit more stable than previous interglacials

Its temperature has been a bit lower than previous interglacials

Here is a chart showing the pattern of previous ice ages and interglacials

So about 10,000 years ago a period of stable and much warmer climate began and it is almost exactly 10,000 years ago that humans began to develop agriculture. This is probably not a coincidence.

But although the Holocene has been a bit more stable than what went before this doesn’t mean that there were no changes to the climate during this recent 10,000 year period.

There is now much controversy about the nature and extent of very recent climatic variations, of the warmer and colder periods during the late Holocene, controversy made much, much more intense by the injection of politics and ideology into climate science. Was the Medieval Warm Period (AD 800–1300) as hot as today? How deep was the temperature drop in the Little Ice Age (16th century to the mid-19th century)? The arguments rage.

I want to side step these controversies for the moment although I reference these events elsewhere.

I want to focus on the period from about 9000 years ago to about 5000 years ago. This period was markedly warmer than today, probably at least 2 degrees warmer over all but even warmer in places like the North Pole where it may have been 6-9 degrees warmer than today. The 2 degrees warmer of that period should be compared to the 0.5 – 0.7 of a degree warming in the last hundred years which seems to be engendering such alarm.

This period of warming between 9000 and 5000 years ago is called the Climatic Optimum and was named back in the days when we quaintly thought that warmer was better and colder was bad.

In order to realise just how recent the Climatic Optimum was you should note that it ended only about about 2000 years before Stone Henge and Skara Brae were built.

Another way to realise just how recent this period was is to think about it this way. I am now 57 years old, I can remember 50 years ago and it doesn’t seem such a huge stretch of time. If we assume an average historical life span of 50 years (a bit optimistic but it makes the maths easier), then we are only looking at only 100 lifetimes ago. That’s how recently the planet was significantly hotter than today.

At this time the forests in Siberia went all the way up to the northern arctic coast (now its just tundra). There would have been no ice cap at the north pole and an open polar sea for hundreds perhaps thousands of years. Many of the glaciers that exist today didn’t exist then, all the glaciers in the USA are less than 5000 years old for example.  Tree lines on mountains were several hundred meters higher then than they are now all across the planet.

If the world was significantly warmer 5000 years ago – and no one disputes that it was – it seems to me that one can come to the following conclusions:

The warming occurred in exactly the same general climatic conditions as exist today (ie it was during the Holocene).

The warming was wholly natural and mankind played no part in it.

Nobody is sure about what natural mechanism caused this warming although there are some hypothesis.

As C02 levels 9000 to 5000 years ago were around 260 to 280 ppmv, and this was the average level for the whole of the preindustrial Holocene, the warming could not have been caused by C02 levels.

As we don’t understand what caused this earlier warming but we know it wasn’t C02 then it seems logical to say that what caused this past warming could be causing the present warming.

There is some evidence that the warming was solar in origin – see this tremendous video lecture

The Greenland icecap did not melt – even though the warming went on for thousands of years

Polar bears did not go extinct – even though the north pole ice sheet melted completely and for a long time

Those who strongly believe in the Greenhouse impact of C02 admit that on its own a doubling of C02 would probably only push temperatures up by 1 degree in about a 100 years. The super alarmist projections of 3, 4 or even 6 degrees of warming in the coming century are all based on models showing secondary forcing mechanisms being triggered by the 1 degree of direct C02 warming. During the Climatic Optimum, even though the temperature was 2 or more degrees warmer than today for a long time, the temperature did not accelerate upwards because there was no triggering of feedback mechanisms.

Makes you think doesn’t it?