evidence: But human activities are changing earth's natural greenhouse effect with a dramatic increase in the release of greenhouse gases. Scientists agree greenhouse gases are the cause of global warming and climate change. [...] CO2 is released through natural processes, such as volcanic eruptions, plant respiration and animals and humans breathing. But the atmospheric CO2 concentration has increased by 50% since the Industrial Revolution began in the 1800s, due to human activities like the burning of fossil fuels and large-scale deforestation. Due to its abundance, CO2 is the main contributor to climate change. [...] It increases as the earth's atmosphere warms but unlike CO2, which can remain in the earth’s atmosphere for centuries, water vapour persists for only a few days.