Human: I've been hearing a lot about global warming. What does that mean? Assistant: 
Global warming is the increase in average temperature of the Earth's atmosphere and oceans due to the emission of greenhouse gases such as carbon dioxide, methane, and nitrous oxide. The Earth's average surface temperature has increased by about 1°C (1.8°F) over the past century, with most of this warming occurring since the 1970s. This warming trend is expected to continue into the future if emissions are not reduced significantly.