The Earth’s history has gone through many cycles of climate change of much larger magnitude than the change that we are facing today. It then begs the question of why we are so concerned about the present climate change. The answer is obvious. Those earlier climate changes happened before the several thousand years of human civilization. The Earth will survive the present climate change, but human civilization may not be unscathed.
The glacial-interglacial cycles (aka ice ages) have been the largest natural climate cycles in the past million years. The figure below, from the article ‘Global Temperature Change’ by Hansen et al., shows the temperature from the most recent interglacial-glacial cycle derived from Antarctic ice core. The global averaged temperature change is about half of the range shown in the figure. This temperature cycle is reconstructed from ice-core record obtained from the Russian Vostok Antarctic base. The Vostok ice core, of 3310 m in length, represents 422,766 years of snow accumulation.
From this figure, the global average cooling rate during the last glacial period—about 5 degrees Celsius over 100,000 years—is about 0.005 degree of cooling per century. The average warming rate during the last interglacial period—about 5 degree Celsius over 12,000 years—is about 0.04 degree of warming per century. This most recent interglacial warming had reached its peak several thousands of years ago. This was followed by a slow natural cooling trend in entering a glacial period.
Then warming, mainly driven by greenhouse gas emissions from agriculture and the burning of fossil fuels and biomass, began around 1900, as shown in the figures below from climate.gov.
For the current anthropogenic warming, the warming rate for the past 30 years and the projected warming rate for the next century is about 2 degree Celsius per century—this is over 400 times the cooling rate in the glacial period and over 50 times of the warming rate in the interglacial period. This current rapid warming has completely overwhelmed any natural climate cycle. So if the human race carries on business as usual, there won’t be another glacial cooling.