Greenhouse gases (GHGs, or "heat-trapping" gases) trap heat radiation in the atmosphere. The four main GHGs are water vapour, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). These gases absorb heat reflected by the Earth instead of releasing that heat to space. The greenhouse effect makes Earth habitable by keeping temperatures at a suitable level for life as we know it. Human activities, such driving a car, burns fossil fuels and emits GHGs. GHGs in the atmosphere have increased since the industrial revolution (1750). Current levels of known greenhouse gases, like methane and carbon dioxide, in the atmosphere are also the highest they have been in more than 650,000 years. GHGs are referred to as drivers of climate change because their presence in the atmosphere alters the Earth’s energy balance by trapping heat in the atmosphere. Land-use practices such as agriculture also emit GHGs and are another example of a climate change driver.
