Prehistoric changes in climate do not disprove current climate science

If you look up "climate" on Twitter, chances are you will come across skeptics of human-caused climate change, using scientific data to prove that the climate of Earth has been changing for hundreds of thousands of years, predating the rise of fossil fuels and the industrial age. For example, in the viral tweet below, a graph made by the Utah Geological Survey is used to show that temperatures have been fluctuating for over 400,000 years, particularly as it coincides with the glacial cycle. 

Other examples of this sentiment can be seen here and here.

At least five major ice ages have occurred throughout Earth’s history. The timing is governed to a large degree by predictable cyclic changes in Earth’s orbit, which affect the amount of sunlight reaching the Earth’s surface. Also, a significant trigger in initiating ice ages is the changing positions of Earth’s constantly-moving continents, which affect ocean and atmospheric circulation patterns. Currently, we are in a warm interglacial (the warm period between glacial periods) that began about 11,000 years ago. The last period of glaciation, informally called the “Ice Age,” peaked about 20,000 years ago. Yes, we do have scientific data that global temperatures were lower during these glacial periods. All of this fails to address the significant differences between pre- and post-Industrial Revolution climate data.¹ Also this variability does not explain the observed warming since the 1950s. Human and natural factors both influence the earth’s climate, but the long-term trend observed over the past century can only be explained by the effect of human activities on climate. Therefore, we find the claim that the Earth's climate has been changing naturally over millennia misleading. It is the consensus of the majority of scientists that the increase in heat-trapping gasses in the atmosphere is warming the planet at unprecedented speed since the mid-20th century.²

As stated by Prof. Jason Donev from the University of Calgary.

Presently, we are experiencing an abnormally long interglacial called the Holocene that has lasted nearly 11,000 years. A new glaciation has been expected to begin; however, due to human induced climate change or anthropogenic climate change, the next glaciation is being delayed anywhere from a few thousand to hundreds of thousands of years. Therefore, it is expected that the Holocene interglacial may last at least another 150,000 years.^[6]

Newswise reached out to our experts to respond to this claim. Here is what Andrew Dessler, Professor of Atmospheric Sciences at Texas A&M University had to say...

It is true that climate changes without any human influence, as ice ages demonstrate.  However, it is a logical fallacy to therefore conclude that humans cannot influence the climate.  In fact, the scientific community has demonstrated beyond a reasonable doubt that human activities are dramatically perturbing the climate system.

Of particular note, changes in carbon dioxide play a key role in generating the ice ages and this provides strong confirmation that human additions of carbon dioxide to the atmosphere will warm the planet.

Largely by burning fossil fuels for energy, we humans have already heated the planet by an average of 1.1 degrees Celsius since 1880. Much of the warming has occurred in the last 40-50 years, at a rate of roughly 0.15 to 0.20°C per decade. If the rise in carbon dioxide continues unchecked, warming similar to the rise in temperatures out of the last ice age can be expected by 2100. This speed of warming is more than ten times the speed of warming that occurred at the end of an ice age, the fastest known natural sustained change on a global scale.³

1. https://www.bloomberg.com/news/articles/2020-12-02/global-temperatures-already-1-2-c-above-pre-industrial-levels 

2. https://climate.nasa.gov/causes/

3. https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/question-6/