A study by King et al. examining extreme climate events has found that humans most likely triggered the last 16 record-breaking hot years on Earth, up to 2014. They determined that this influence on global climate goes back as far as 1937, an effect that has been masked until recent decades by the wide use of industrial aerosols, which have a cooling effect on temperatures. The researchers concluded that without human-induced climate change, recent hot summers and years would not have occurred.
Lipuma, L. (2016), Researchers attribute human influence on climate back to 1930s, Eos, 97.