Although it is certain that Earth has naturally warmed up and got colder during other eras, such cycles have always been much slower, taking millions of years, whereas now, within a period of just 200 years, we are reaching levels that in the past brought about extinctions.
The IPCC is an intergovernmental body of the United Nations, dedicated to providing the world with an objective, scientific view of climate change, its natural, political and economic impacts and risks, and possible response options. It’s the most up-to-date and comprehensive explanation of the science of climate change and the future of Earth. Their findings cannot be ignored.
Their latest report (2018) warns that the world has already warmed by 1°C since the middle of the 19th century, and could reach 1.5°C before the middle of this century at the current rate of warming.
Experts agree that the Industrial Revolution was the turning point when emissions of greenhouse effect gases entering the atmosphere began to soar. The Industrial Revolution was itself borne out of smaller revolutions: agricultural, technological, demographic, transport, finance… creating a new model of production and consumption.
So, the Earth’s average temperature has increased 1.1 degrees Celsius since the late 19th century. It may sound like a small amount, but it's an unusual event in our planet's recent history. Earth's climate record shows that the global average temperature is stable over long periods of time. Furthermore, small changes in temperature correspond to enormous changes in the environment.