As I have explained above, the climate system is much more sensitive to even small perturbations than most people think. Another way of showing this fact is to look at human impacts on the climate before industrialisation. 

Since the rise of agriculture, human activities on Earth have played a role in shaping ecological and climatic conditions. There is good evidence to suggest that the rise of agriculture actually had a positive (amplifying) feedback on early climate, hindering a new ice age to occur. 

Atmospheric CO2 and CH4 increases during the last few millennia are anomalous compared to preceding interglacial periods. The same time period when agriculture spread across the continents and emitted greenhouse gases by clearing forests for crops and pastures, domesticating livestock and burning crop residues. Suggesting that emissions were large enough to warm climate and prolong the natural interglacial warmth.

Ruddiman et al. (2016) show evidence for what seems to be a trend brake in naturally falling CO2 and CH4 concentrations some 6000-5000 years ago, towards increasing concentrations most likely driven by anthropogenic forcing.

We know that agriculture spread across the world during this time period. Agrarian civilisations started to flourish along the Nile, Tigris, Euphrates, Indus and Yellow River some 7000-5000 years ago. Cultivation was dependent on flow and ebb cycles that in turn relied on seasonal rains and melting snows packs in the mountains. These formed the conditions for production of surplus food (energy) which allowed societies to expand and grow more complex.

Ruddiman and colleagues show how the development of irrigated rice paddies in Asia and widespread livestock domestication some 5000 years ago coincides with increases in methane emissions. Just like today, forests were cut down, vegetation slashed and burned to make way for agriculture all across Eurasia, Africa and the Americas. This generated CO2 emissions which in turn impacted climate. 

Archeological data records a shift from forest cover to more open vegetation in northern and central Europe that began som 6000-5000 years ago and was complete by the start of the industrial era. Similarly, early deforestation was likely caused around the Mediterranean by extensive land use by Greek and Roman civilisations. In Britain and France, forests had already been reduced to near-modern levels by 2500-2200 years ago.

East central China had widespread forest cover until 8000 years ago, followed by a persistent decrease especially after 6000 years ago. Archaeological sites, proxy for population density, in central China increased thirtyfold between 8000–7000 and 5000–4000 years ago. By 4000 years ago, coal had come into use as a fuel source in the Yellow River Valley because of lack of wood. Deforestation of southern China during the spread of rice agriculture after 5000 years ago added to the ongoing CO2 increase.

In India, sedentary farming and clearance emerged between 5000 and 3500 years ago, with especially rapid settlement expansion on the Deccan Plateau and in the Ganges plains. 

All this evidence provides support for the idea that large-scale deforestation led to a rise in CO2 during the middle and late Holocene. Many models have missed this because they assume low population numbers and small forest clearance per person and thus show low emissions. But this doesn't fit with historical evidence of larger per capita forest clearing 2500-1000 years ago than during industrial times. Probably because land use was inefficient and required large amounts of land but became more intensive over time as agricultural methods changed.

The simulation above indicates much greater deforestation during the millenia preceding the industrial era in agreement with pollen evidence. In contrast, standard reconstructions that assume small constant per capita clearance during preindustrial times show 40-80% of forest cover still persisting in Europe by the year 1800. Meaning massive deforestation must have taken place within the last 200 years to explain current low forest cover. But this doesn't fit with historical evidence of pervasive reforestation in western and central Europe since 1800, not deforestation. 

Main point: The Holocene climate was partly a consequence of human feedbacks on the climate system

Changes in temperature and precipitation have always impacted people by affecting what they could and couldn't grow to harvest food (energy) for survival. 

The climate stabilised about 7,000-5,000 years ago coinciding with the flourishing of agrarian civilisations along the Nile, Tigris, Euphrates, Indus and Yellow River. Cultivation was dependent on flow and ebb cycles that in turn relied on seasonal rains and melting snows packs in the mountains. These formed the conditions for production of surplus food (energy) which allowed societies to grow more complex.

But agrarian societies have always been vulnerable to climatic changes. Sudden cooling events or extended droughts caused widespread famines and sometimes collapsed entire communities. Especially vulnerable were those who relied on single crops or undermined the ecological base for survival for example through intense deforestation. 

For example, a sudden cooling that happened around 3,700 to 3,000 years ago greatly influenced populations in Asia. The most dramatic changes were seen in high latitude and high-altitude areas in Mongolia and the Tibetan Plateau. Crops started to fail and widespread famine took hold. This forced people to migrate, shift to more cold resistant crops, or turn to pastoralism. Cooling temperatures also affected Northern China between AD 291-360, a time when the Chinese capital was relocated from Xian to what is now Nanjing, in the south. Again, people would have had to adapt by migrating, changing crops, herding cattle or trading. It was not an easy process and lots of conflicts arose.

The difference now is of course that the rate of change is much more rapid and that its becoming hotter, not colder, which humans have had less of an experience adapting to. Furthermore, there are no virgin lands left to move to when one region becomes uninhabitable, the world is full and most ecosystems severely degraded. Using migration as a tool for adaptation doesn't work that well anymore. We have also become heavily reliant on just a few crops and undermined diversity by eradicating species. This makes our current civilisation very vulnerable to a changing climate.

Main point: Humans can adapt to a changing climate but this time the rate of change is much more rapid and migration is not a good option