Over the last 1 million years, Earth has oscillated between ice ages and warmer periods [1,2]. This was not caused by humans, but by changes in the energy radiated by the Sun , the Earth’s orbit around the Sun, and the angle at which the Earth rotates [3,4,5].
These changes in temperature were very gradual , with no more than 1°C of change in the global average temperature over the past 10 thousand years . This stability facilitated the development of human civilisation .
Nowadays the Earth is warming abnormally quickly . Over the past century it has warmed roughly 10 times faster than the average increase in temperature after each ice age .
Despite there being similarly rapid and large changes in temperature in the distant past [8,10], current global warming is dangerous because humans have not experienced changes of this scale and speed before . Increasing temperatures will affect our ability to produce food, access clean water  and cause rising sea levels  so if this change happens too quickly it will be challenging for us to adapt [14,15].
 https://earthobservatory.nasa.gov/features/GlobalWarming/page3.php (First graph)
 https://earthobservatory.nasa.gov/features/GlobalWarming/page2.php (Paragraph 1)
 https://earthobservatory.nasa.gov/features/Milankovitch/milankovitch.php (Numbered list)
 https://science.sciencemag.org/content/339/6124/1198/tab-pdf (Page 1200 Paragraph 1)
 https://www.pnas.org/content/111/34/E3501 (Figure 1 Look at variation over past 10,000 years)
 https://www.bbc.co.uk/history/ancient/british_prehistory/overview_british_prehistory_01.shtml (The dawn of farming PARAGRAPH 5)
 https://www.pnas.org/content/pnas/115/52/13288.full.pdf (Page 13291 Paragraph 2)
 https://earthobservatory.nasa.gov/features/GlobalWarming/page3.php (Paragraph 3)
 https://www.nature.com/articles/nature06588 (Final Paragraph)
 https://www.pnas.org/content/pnas/115/52/13288.full.pdf (Abstract and Paragraph 1)
 https://www.ipcc.ch/sr15/chapter/spm/ (B.5)
 https://www.ipcc.ch/sr15/chapter/spm/ (B.2)
 https://www.pnas.org/content/pnas/115/52/13288.full.pdf (Significance Box)
 https://www.pnas.org/content/pnas/107/21/9552.full.pdf (Last 3 paragraphs)
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