[Music] hi and welcome back to three science lessons code UK by the end of this video you should be able to describe what's meant by the greenhouse effect in terms of short and long wavelength radiation you should then be able to state the main greenhouse gases over the next couple of videos we're going to be looking at how human activity is changing the atmosphere and this will include climate change now one key part of climate change is the greenhouse effect so we're going to be exploring that in this video in the last video we saw that the atmosphere contains two main gases around 78% is nitrogen and around 21% is oxygen the remaining 1% consists of many different gases I'm showing you three here the amount of water vapor in the atmosphere is variable and that changes depending on the temperature the atmosphere contains around naught point naught 4 percent carbon dioxide on tiny amounts of methane now water vapor carbon dioxide and methane are all greenhouse gases and you could be asked to name a greenhouse gas in you exam so let's take a look at what greenhouse gases do in the atmosphere it's very important that you learn the following I'm showing you here a diagram of the earth and the atmosphere I should point out that this diagram is not to scale in reality the atmosphere is much thinner than I'm showing it here energy from the Sun travels to the earth as short wavelength radiation for example ultraviolet and visible-light some of the short wavelength radiation simply reflect back into space but most of it passes easily through the atmosphere that's because short wavelength radiation does not interact strongly with the gas molecules in the atmosphere the energy of the radiation is now absorbed when it reaches the surface of the earth the surface of the earth now radiates the energy as long wavelength radiation such as infrared now some of the long wavelength radiation interacts with the greenhouse gas molecules in the atmosphere in other words the energy and the long wavelength radiation is absorbed because the energy is trapped in the atmosphere this causes the temperature of the atmosphere to increase now there's one really important idea about the greenhouse effect the greenhouse effect actually keeps a temperature on earth warm enough to support life in fact without the greenhouse effect the earth would be too cold for most living organisms to survive in the next video we're going to look at how the levels of greenhouse gases are changing and the effects that this will have on planet Earth remember you'll find plenty of questions on the greenhouse effect in my vision workbook and you can get that by clicking on the link above [Music]