General Science Class-8 (MCQs=1674)

For climate change, the most important greenhouse gas is carbon dioxide, which is why you hear so many references to “carbon” when people talk about climate change. There are three main reasons CO2 is so central to the global warming happening today. First, there is just so much of it: we now add over 35 billion tons of CO2 to the atmosphere every year, mostly by burning carbon-rich fuel like coal and oil that had previously been trapped in the ground. Second, it lasts a long time in the atmosphere. The CO2 we emit today will stay above us reflecting heat for hundreds of years. This means that, even if we stop all new CO2 emissions tomorrow, it will take many lifetimes before the warming effect of our past emissions fades away. Finally, many different industries rely on carbon-rich fuels or other processes that give off CO2. That includes burning fossil fuels for electricity and heat and to power our vehicles, but it also includes manufacturing concrete and steel, the refining process for raw oil and gas, fermentation (for instance, to make alcohol or pharmaceuticals), and the decay of plant matter (like after trees are cut down). All of these sectors can make changes to emit less CO2, but the same solutions won’t work for all of them. Infographic: Other greenhouse gases. CO2 is the biggest cause of human-made climate change, but other greenhouse gases are important too. They come from different sources, linger in the atmosphere for different amounts of time, and may be more or less potent at trapping heat. Greenhouse gases are usually counted in “CO2 equivalents” (CO2e). One CO2e is the amount of heat an equal amount of CO2 would be expected to trap over the next 100 years.