The Earth’s climate has been changing since the beginning of time. In fact, it has been an extremely dynamic place over the last 4.5 billion years or so. These changes have resulted in a wide range of conditions, including periods that were very cold and others that were extremely warm.
Scientists have been aware of this pattern for some time. However, what they didn’t know until recently was that this variability was being caused by human activity.
The industrial revolution began in the late 18th century, and with it came an increase in greenhouse gas emissions from factories and other sources. This was due to the burning of fossil fuels such as coal and oil for energy production and transportation purposes (e.g., cars).
As more carbon dioxide entered the atmosphere through these activities (and others), temperatures began to rise globally starting around 1900. By 1940, scientists were noticing a clear trend toward warmer conditions across many regions around the world—particularly in North America, Europe and Asia—and by 1975 it was clear that Earth was undergoing a period of rapid warming. This trend continued into 2012 when average global temperatures reached record highs not seen since 1880.