One of the most intriguing and challenging question that intelligent people ask me when discussing global warming is "WHAT TRIGGERED THE END OF THE LAST ICE AGE, considering humans were not indulging in burning fossil fuels?"...

Very very good question if you ask me... The answer of course is complex and not specifically due to a singularity... but to a confluent of happenings... There is a "natural" carbon cycle which has been observed through the record by studying ice cores. In this "natural" cycle there are ice ages and warmer climes... We know that. 

To some extend we must consider that there is a certain natural balancing act between LIFE, the OCEANS and the ATMOSPHERE that, like a rope-walker will steady itself within limits trough various loops of gaseous exchanges, of albedo and of natural sequestration of carbon. Shake the rope and the walker might fall off.
The natural cycle might shift its limits to unknown values... We know that for the last 500,000 years these "normal" limits ranged from 180 to 300 ppm of CO2 in the atmosphere with corresponding variations of up to 10 degrees Celsius accordingly. We know that photosynthesis on the surface of the planet is equivalent to about six times the energy consumed by human activities. 
The variations of the balance are influenced by the sun cycles, the Milankovitch cycles (the earth wobbles on its axis and trajectory), volcanic activity of various kinds and of course LIFE as a whole which through progression and extinction can influence the carbon cycle in its absorption and/or release of CO2 and of oxygen, while being influenced by the variability in atmospheric humidity, in which the dew point plays an important sign-posting role... The dew point of course refers to the meeting point of atmospheric pressure (also influenced by altitude), of humidity and of temperature at which "water condensation" forms... Rain, fog, dew, clouds...

But many people, including intelligent people, like a simple answer akin to "THE BUTLER DID IT"... If you hit your finger with a hammer, you know where the blow came from. Simple. But this ain't the case here. It is a big planet with a thin atmosphere. We might point the finger at something that had only a small influence on "the next" and it may not upset the balance for thousands of years. 

But we also know, sometimes small triggers can engender a big shift... It's a bit like using a command key on a pad that tells a 12 volt relay to turn on the electricity for a 440 volt engine that will turn a screw that will open megaliters floodgates in a 500,000 acres paddock.
In Chaos theory, the Amazon butterfly conundrum event-possibility is also well-known... But when a system is well balanced, small influences will soon die in the bum. UNLESS.

The ice record for the period 14,000 to 10,000 years ago —the last big melt — shows an unusual amount of ash from FOREST FIRES. Some palaeontologists attribute these fires to humans burning off forests to open "grasslands" for cultivation or hunting. The ash and the burning would have created an atmospheric conflict. It would have increase the particle amount in the atmosphere, thus should have induced cooling, but the burning also released large amount of CO2 that the forest were not reabsorbing straight away. The CO2 would have warmed up the atmosphere first as a warming gas and second as it interfered with water vapour behaviour. It is possible that at the same time, the sun cycle was also "hot" and the coincidences and convergence of effects, including that of the Milankovitch cycles started the big melt... A few years of warming can start a chain of events.

One situation that is is rarely acknowledged is that as the sea level rose, the land altitude decreased in this relationship... THUS THE LAND WAS WARMING UP due to changes in its "elevation" as the sea level rises. For the 100 metres the sea rose during the last ice age melt, this added 0.65 degree Celsius to the land surface "global warming", then... This is not negligible.  

Of course on such large system as the climate of the planet there are some variations, some elasticity in the reaction times and various reactivity in the climatic zone of influence. Elasticity, flexibility and fluidity are three of the most important qualities of matter once passed the obvious gravitational force and atomic forces. Climate cannot escape the chaotic properties of flexibility, fluidity and elasticity... This is why there are variations to the "same atmospheric conditions". These variations are influenced by surface composition: colour, height and amount of land versus the amount of sea...
One should note that the last big melt was VERY rapid compared to other similar changes on the surface of the earth... Thus one can guess that the natural melt that would happen over say 25,000 years was "speeded up" by something, including the forest fires...  Note that volcanic activity, usually associated with cooling could have had the "strange" reverse effect by darkening the colour of some ice sheets with thick black ash, adding to that of the forest fires, making them more prone to absorb the heat of the sun, thus change the albedo and melt accordingly. This is another theory that can hold its own... 
One has to also assess the work by the Swedish Scientist Arrhenius who postulated that during ice ages, the store of CO2 in the atmosphere is about 45 per cent less than during warmer periods... This complex study for the time has since been confirmed by experiments and by the study of the record that shows this relationship with a certain precision. 
Until the early 1940s, scientists were working on the assumption that the earth was slowly going back into an ice age. Most study of the temperature over since the last melt shows a slow decrease after a quick spike. The figures since the middle ages that had also showed a general cooling trend but by mid last century they did not add up anymore.. In the early 1950s, scientists noticed a warming contrary to the expected trend. 
Scientists knew of the work of Laplace, Fourier, Arrhenius and another scientist Arvid Högbom who also postulated in 1897 or such that the industrial revolution was contributing as much CO2 into the atmosphere than the planet living system... At the time, no-one thought seriously about it.
But now we know. Scientific knowledge is a strange beast that always needs refinement. 
For example, in the 1930s, most science books were placing the dinosaurs still happily living about 6 million years ago... Of course this figure has since been revised and science knows that the extinction of the big (and small) beasts happened around 65 million years ago, over a one million year period. 
Science has refined its dating techniques and its data collection to the point that we now know GLOBAL WARMING IS HAPPENING and is at least 95 per cent driven by human activities, mostly that of burning fossil fuels... One can argue with rubbish argumentation, emotions and doubts while getting blue in the face against the science, but the science is clear and getting clearer. 
The prognostic is dire. 
--------------------------------------

IF you live in Brisbane, Perth or Darwin, then the year 2042 could be the year when your climate is shoved beyond anything humans there have ever likely experienced before.

From that point onwards, at least according to a new study in the leading science journal Nature, even the coolest years will be hotter than any record breaking scorchers you or your relatives might have experienced over the last 150 years or so.

For Sydneysiders, the study finds this "timing of climate departure" comes around four years earlier, in 2038. People in Canberra and Melbourne get 2045 as the year when their climate "shifts beyond historical analogues". Adelaide catches up in 2049.

For the entire globe, the year 2047 is the point when annual average temperatures move permanently outside modern day boundaries, according to the study.

All these dates are dependent on what the world does about its growing emissions of greenhouse gases that mainly come from burning fossil fuels, making cement and clearing land and forests. If there are no genuine moves to cut emissions, then the study claims these are the years we can look forward to.

If action is taken and emissions are quickly stabilised (no genuine sign of that at the moment), then the climate threshold in our Australian cities is crossed between 24 and 31 years later, depending on where you live. For the globe, stabilising emissions means the threshold is crossed 22 years later, in 2069.

Lead author Camilo Mora said of his study:

The results shocked us. Regardless of the scenario, changes will be coming soon. Within my generation, whatever climate we were used to will be a thing of the past.

To carry out the study, the 14 authors from the University of Hawai'i used 39 different computer models of the earth's climate system. They used the models to first recreate the years 1860 to 2005, and to then project into the future

---------------------------
So 2047 is for when the whole planet climatic system gives itself a massive kick in the butt... Well, this has been calculated CONSERVATIVELY. Gus has placed this figure at 2032 (18 years and five months from today) for the last ten years, while considering the scientific record and the amount of CO2 that humans have added in the atmosphere, adding plots in the middle range of the bracketing...
Though I can be flippant about it, I believe I am correct. it's 2032.
In relation to natural climate variations over aeons, the present change is going at lightning speed...
We're in a quandary... we really don't know what to expect except more warmth, more frequent stronger storms, more heat-waves and sudden cool blizzards. We suspect that temperate regions will suddenly become subtropical with massive cool blasts from the poles (especially in the northern hemisphere), making cultivation and weather prediction very difficult. This is what I have called "winters like summer and summers like hell", but the heat will have some weird short flips into cold influences from the polar regions that are melting at pace. As well, some deserts will get hotter though some might start to collect more water in massive bursts... and then dry out in a jiffy... The speed of change will become mind-boggling. 
The weather as we know it is going to become far more extreme — more heat for longer periods, with really super-hot days and with strong storms plus sudden short cold snaps at the wrong time of the year. As well the sea level is going to rise faster than we could imagine... The Aboriginal people were driven out of the Arafura Plains when it became a sea...
So what induced the last big ice age melt?...
Study of the ice cores shows CO2 was the major driver of the melt... Some scientists point to anomalies in the travel of the earth around the sun, as calculated in the Milankovitch cycles... But most scientists are convinced that the effect would have been minimal... And an increase of CO2 was the culprit definitely. But where did the CO2 come from?... 
Studies also show that the Sahara Desert was heavily forested until 10,000 years ago... Would the loss of this single large forest have contributed to the big melt as well? Why did the forest disappear?... It does not take much "dryness" to start killing off trees — trees that may have been used to cooler wetter conditions — and be taken over by shifting sands. Electric storms could have started massive fires, the whole process snowballing and accelerating the change of climate. 
CO2 was the culprit...
The next question is like a Dorothy Dixer.
"DO you think that we'll be able to reduce our emissions of CO2 to arrest the progress of global warming?"... The answer to this of course is a simple NO... NO! Alas, no.... As long as our economy is driven by greed and is separated from the REAL value of the environmental conditions of this planet, we've got zero chances... China might be our best chance, though, should the climatic conditions flip very rapidly in that country. And say greed in China is still in its infancy compared to that driving the US economy, where debt and more debt fuels the downhill run towards this crazily hot future.
Major global warming catastrophes could happen as soon as 2015. So far we've only seen minor catastrophes like intensified storms and tornadoes.
...

An article published in Current Anthropology in 2010 revealed that a fertile landmass now submerged beneath the Persian Gulf may have been home to some of the earliest human populations outside Africa.[9][10] 

Jeffrey Rose, an archaeologist and researcher with the University of Birmingham, says that the area in and around this "Persian Gulf Oasis" may have been host to humans for over 100,000 years before it was swallowed up by the Indian Ocean around 8,000 years ago. Archaeological sites in Yemen and Oman have yielded a stone tool style that is distinct from the East African tradition. This raises the possibility that humans were established on the southern part of the Arabian Peninsula beginning as far back as 100,000 years ago.[11] The Persian Gulf links up Iran (ancient Persia), Saudi Arabia and Iraq (the ancient region of Southern Mesopotamia). A map published in the Journal "Current Anthropology" shows regions of the Arabian Peninsula that were exposed as sea levels fell, and hence supposes that people of that region became environmental refugees around 8000 years ago.[12]

-------------------

So what did trigger the last ice age big melt?... One could say, the last big melt was part of the natural carbon (CO2) cycle of surface carbon at the time. But the big melt was "accelerated" by other factors such as forest fires and consequently rising sea levels (sea rose 100 metres). Since this big melt, the planet surface has been going towards an ice age gradually, somewhat naturally, till the industrial revolution... Since then, the planet has been warming up, and despite "a slow down" in the warming for the last 15 years, this warming is actually accelerating.

What is the cause of this warming trend?
THE SAME CAUSE AS THE LAST ICE AGE BIG MELT: CO2. 

This time the CO2 is simply coming from humans burning off fossil carbon... ADDING the million years sequestered carbon back into the surface carbon equation, at a rate of knots.
It might take several million years for "nature" to sequester a certain amount of carbon. Humans will burn the same amount (reintroduce it into the atmosphere) in less than six months...

Do the sums. It ain't looking good.

Yours, as always,
Gus Leonisky