How long has climate change been around?
Earth’s climate has been changing since it was formed. Sometimes the climate changed quickly, other times more gradually, but there has always been climate change. Before humans this was caused by natural factors such as the strength of the sun, volcanic activity, even meteor impacts. For example, at the time of the dinosaurs, 250 – 65 million years ago, the global climate was hot and humid. Over the past million years, the Earth has gone through cycles of ice ages, where Earth’s surface temperature warmed and cooled by about 5 C every 100,000 years.
But if we ask: “how long has climate change caused by humans been around?” most scientists agree this started around the time human activity began to produce a lot of carbon dioxide. This happened about 200 years ago, at the start of what’s known as the Industrial Era. This is when coal-powered mechanical devices replaced human and animal labour and at the same time the number of humans on earth increased rapidly. Together these changes led to humans emitting more and more carbon dioxide into the atmosphere, and the beginning of human-caused climate change. Some scientists have argued that the earth was headed for another ice age around now, but the carbon dioxide produced by humans starting in the 1800s prevented this.
The screenshot below is from the Global Carbon Atlas. This is an interactive site that shows how human impact on the climate has changed through time- worth checking out. http://www.globalcarbonatlas.org/en/outreach (click on Enter the Past).
Finally, the graphs below can help you work out when climate change caused by humans started. The left-hand graph shows how global temperatures have changed over the last 2020 years. The right-hand side zooms in on the time since 1850 (when the temperatures are based on direct observations using thermometers). It compares the observed climate change (black line) with climate change simulated from a model that includes only natural factors like changes in the sun and changes in volcanic activity (green line), with climate change simulated by a model that includes both human and natural factors (orange line). The black line of the observations follows the orange line quite well, but both of them pull away from the green line starting around 1950. From this we can say that the climate change caused by humans has been around since at least 1950.
