It's not that anyone was following anything at all 500 years ago, but it was still a given in the on-going life and cycles of this planet.
Over at least the past million years,
glacial and interglacial cycles have been triggered by
variations in how much sunlight reaches the Northern Hemisphere in the summer, which are driven by small variations in the geometry of earth’s axis and its orbit around the sun, but these fluctuations in sunlight aren’t enough on their own to bring about full-blown ice ages and interglacials. They trigger several
feedback loops that amplify the original warming or cooling.....
During an interglacial:
- sea ice and snow retreat, reducing the amount of sunlight the Earth reflects.....
- warming increases atmospheric water vapor, which is a powerful greenhouse gas......
- permafrost thaws and decomposes, releasing more methane and carbon dioxide.....
- the ocean warms and releases dissolved carbon dioxide, which traps even more heat.
These feedbacks
amplify the initial warming until the earth’s orbit goes through a phase during which the amount of northern hemisphere summer sunlight is minimized. Then, these feedbacks operate in reverse, reinforcing the cooling trend.
The change in temperatures can be anywhere between 5º to 15º
It was partly through their attempts to understand
what caused and ended previous ice ages that climate scientists came to understand the dominant role that carbon dioxide plays in earth’s climate system, and the role it is playing in current global warming.