A video viewed thousands of times online disputes the reliability of an authoritative graph showing cooling global temperatures over 1,000 years and rapid warming in the 20th century. A speaker in the clip claims the chart falsely inflates the impact of man-made climate change. However, the graph is a reliable marker of warming temperatures largely as a result of human activity, climate experts told Reuters.
https://www.reuters.com/article/factcheck-climate-change-idUSL1N2S112H
In each case, the outcome was clear: global mean temperature began to rise dramatically in the early 20th century. That rise coincided with the unprecedented release of carbon dioxide and other heat-trapping gases into the earth's atmosphere, leading to the conclusion that industrial activity was boosting the world's mean temperature. Other researchers subsequently confirmed the plot.
https://www.scientificamerican.com/article/behind-the-hockey-stick/