This claim is 100% true. Climate change is not a natural cycle, and is completely caused by human activity. Since the late 1800s human activities have released CO2 (carbon dioxide), CH4 (methane), N2O (nitrous oxide), and fluorinated gases into the atmosphere. Scientist have measured the earth's change of climate by tracking ice/glacial melting, ocean sediment, and studying the ozone layer.
The release of these gases have caused the earth's climate to change unnaturally, and not just warming. Extreme weather events such as floods, hurricanes, and snow storms have become even more severe but also more frequent. There has also been loss of biodiversity because of these weather events that have gotten to be irreversible.
Volcanic eruptions and the sun's energy do also lead to the release of greenhouse gases into the atmosphere, but do not compare to the amount that humans have released.
Causes of Climate Change - EPA