Yes, scientists are confident that humans are responsible for global warming.

Earth´s temperature depends on the balance of energy entering and leaving the Earth system. Factors that can cause this balance to change include the amount of energy from the sun that reaches the Earth, how much of the energy is reflected back into space, and changes in the greenhouse effect. The greenhouse effect is the effect of certain molecules in the atmosphere (such as CO₂, methane, water) to trap some of the heat that the Earth radiates back onto space after it has been warmed by the sun; increasing the concentration of greenhouse gases in the atmosphere causes the average temperature at the Earth´s suraface to increase. Since the mid-20th century, the sun´s average energy output has been constant, and changes in reflectivity (largely from human emissions of particulate pollution into the atmosphere) have actually had a slight cooling effect. On the other hand, levels of greenhouse gases, such as carbon dioxide and methane, in the atmosphere have risen dramatically since the Industrial Revolution.

Before 1750, there was about 280 parts per million (ppm ) of CO₂ and about 700 parts per billion (ppb) of methane in the atmosphere; today CO₂ levels have risen to about 390 ppm and methane levels have more than doubled to about 1800 ppb (parts per billion). This increase in greenhouse gases can be attributed human activities, especially burning fossil fuels like oil and coal.

According to the Hawaiian Volcano Observatory, Kilauea, a single volcano on Hawaii, emits between 8,000 and 30,000 metric tons (1 metric ton = 1000 kg) of CO₂ each day. The total CO₂ emissions from volcanoes worldwide, on and land and under the sea, is estimated to be 260 million metric tons per year. Compare that with the 33 billion metric tons of CO₂ emitted by humans burning fossil fuels; volcanoes emit <1% of the amount of CO₂ that humans emit. In addition to releasing CO₂, large volcanic eruptions can also release small droplets of sulfuric acid and ash high into the atmosphere, where they reflect incoming solar radiation, temporarily decreasing the temperature at the Earth´s surface.