evidence: In the late 20th century, when scientists started looking at how temperatures have changed over time, they observed a much faster rate of planetary warming from the 1980s than had previously been recorded. [...] And, as a result, Earth started warming faster. [...] Benjamin Cook, a climate scientist at the NASA Goddard Institute for Space Studies, said back in the late 20th century, when researchers started to look for answers to explain the warming trend, they examined different factors including greenhouse gases, solar energy, ocean circulation and volcanic activity.