if I asked you to think of the most important greenhouse gas what comes to mind carbon dioxide methane perhaps water vapor if you're anything like me you probably think it's a poorly phrased question and you're right it is so why did I ask it well all too often we humans like to oversimplify the world and its mechanics by asking these superficially simple and inappropriately vague questions and when we do we open ourselves up to making mistakes in logic and using fraud reasoning for example it is a fact that over 95% of all the carbon released into the air every year comes from natural sources this means human activity is responsible for less than 5% of total global carbon emissions so does this mean that 95% of the Routan rise in co2 is natural our human emissions really this negligible it's certainly an argument proposed by many climate sceptics in other words human activity is maybe 3% contributing to the 3% of carbon dioxide that's in Earth's atmosphere it's so negligible nature makes up 96.6% of all carbon dioxide emissions so humans overall contribute to any greenhouse effect is something like 0.28 percent of the Earth's atmosphere human beings create only 3% of that point oh four percent over the whole world but there's one glaring problem with this claim just because human activity accounts for less than 5% of the total global carbon emissions it doesn't mean that it accounts for less than 5% of the increase in atmospheric carbon if you've seen my video how much carbon you'll know that in order to truly understand what's going on we have to look at the carbon leaving the atmosphere as well as the carbon entering it when we do this we see that the carbon released by natural processes the 95% is more or less canceled out by the carbon absorbed by natural processes without that extra 5% that we humans are adding there would be no increase in co2 at all in other words that percent of total global emissions is responsible for practically 100% of the rise in co2 this is why it's important to understand facts in context and that brings me back to my question what is the most important greenhouse gas unsurprisingly that depends entirely on context specifically what we mean by important so let's begin every greenhouse gas absorbs infrared radiation at different frequencies and the broader the spectrum of wavelengths a gas absorbs the more potent a greenhouse gas it will be so one could begin to answer the question by simply looking for the gas most capable of absorbing heat so which gas holds this prestigious title well according to current research that title goes hands down to a little-known molecule called sulfur hexafluoride or sf6 made of six fluorine atoms and one sulfur atom this gas has a density five times greater than air and has done the rounds on the internet as a voice deepening gas kind of the opposite of helium in fact this gas is so dense it can float aluminium foil but while sf6 may seem like a fun party trick mucking about with it is incredibly irresponsible because it has a greenhouse effect twenty three thousand nine hundred times more powerful than co2 when compared over a hundred year period and it can hang around in the atmosphere for between 800 and 3,200 years this means your five minutes of fun will have an environmental impact on the planet which far out lives not only you but any living memory of you your kids and your grandkids cheery stuff fortunately a ten parts per trillion the concentration of sf6 in the atmosphere is so tiny that it has a negligible effect on global temperatures it is simply not abundant enough to contribute significantly to the global greenhouse effect clearly then the potency of a greenhouse gas alone is insufficient for us to measure its importance perhaps we should instead look for the abundant once again there is a clear winner here too and considering that 71% of the earth's surface is covered in water it shouldn't be that surprising water vapor as well as being abundant water vapor also has an incredibly powerful greenhouse effect which we can see when we look at the absorption bands of the greenhouse gases in the atmosphere notice the broad range of wavelengths absorbed by water vapor indicated in grey it's such a great abundance and such a broad absorption spectrum it's hardly surprising that water vapor accounts for at least half of the total global greenhouse effect in this sense it is arguably the most important greenhouse gas on the planet indeed many climate sceptics will tell you exactly this water vapor is a far more powerful greenhouse gas than co2 this is because there's so much more water vapor than co2 many of the organizations like National Geographic Natural Resources Defense Council and their like and also their allies and the media focused solely on the man-made gases as the main agents of greenhouse warming they don't mention the most significant greenhouse gas of all water vapor 98% or there abouts of greenhouse gases we're supposed to hold the eight heat in or do older heat in its water vapor and clouds and when you see the graph there's water vapor and clouds here's carbon dioxide the problem with these arguments is that they are not merely claiming that water vapor is the most important greenhouse gas they are doing so with the implicit argument that co2 is by comparison insignificant and that is simply not true you may also have noticed that some of them further misrepresent the science by conflating the relative abundance of water vapour in the atmosphere some ninety percent of all greenhouse gases by volume with its relative contribution to the global greenhouse effect some 50 or 60 percent and they therefore further exaggerate its importance but the main reason that these arguments are flawed is that they fail to distinguish between two different phenomena the global greenhouse effect which is the combined warming effect of all the atmospheric greenhouse gases and global warming which describes the increase in average global temperature water vapor does contribute the most to the global greenhouse effect but when it comes to causing global warming it's an entirely different story this is because the concentration of water vapour in the atmosphere is controlled by global temperature not the other way around warmer air holds more water vapor and vice-versa unlike other greenhouse gases water vapor also doesn't stay for very long in the atmosphere before it forms precipitation because of this its concentration in the air varies massively depending on time temperature and location in order for water vapor to contribute to global warming its atmospheric concentration must increase and this can only happen if global temperatures begin to rise beforehand something else must initiate the warming in the first place this means that while water vapor is an incredibly powerful positive feedback an amplifier of temperature change it can never be the primary cause of global warming so are there greenhouse gases which can trigger global warming well actually yes in theory most of them can but by far the most abundant of these is you've guessed that co2 in fact after water vapor is the most abundant greenhouse gas in the atmosphere and crucially it's concentration doesn't depend on atmospheric temperature nor does it vary significantly by time or location unlike water vapor which predominantly enters the atmosphere via evaporation co2 can enter the atmosphere in a multitude of different ways including volcanic activity forest fires decomposition and ocean degassing some of these processes like ocean degassing are themselves caused by rises in temperature so co2 can behave as a positive feedback an amplifier in the same way as water vapor in fact if we look at the geological record this means we often see that rises in temperature caused rises in co2 unfortunately this is another fact often misused by skeptics but the temperature was the driver here temperature controls the amount of co2 dissolved in the oceans warmer oceans like warmer soda cannot hold as much co2 fizz there were no SUVs industrial smokestacks her coal-fired power stations 650,000 years ago they have now been several may I score surveys every one of them shows the same thing the temperature rises or Falls and then after a few hundred years carbon dioxide follows so obviously carbon dioxide is not the cause of that warming in fact we can say that the warming produced the increase in carbon dioxide co2 clearly cannot be causing temperature changes it's a product of temperature it's following temperature changes this argument is normally used to imply that human activity can't cause rises in co2 or that co2 can't cause warming at all but of course the fact that warming can cause rises in co2 does not mean that all rises in co2 are caused by warming nor does it mean that co2 can't also drive temperature change processes like volcanism or say the combustion of fossil fuels occur regardless of global temperatures at the time and can produce a lot of carbon dioxide in fact when we look at the geological record we can see that changes in the concentration of co2 have been some of the primary drivers of climate change on the planet so co2 may not have the most powerful greenhouse effects or even be the most abundant but it doesn't have to be it is simply the most abundant gas capable of causing global warming and that makes it very important indeed for comparison the next most abundant is methane which though some 20 times more potent as a greenhouse gas is measured in parts per billion while co2 is measured in parts per million this means there are several orders of magnitude difference in both atmospheric concentration and global emissions which more than mitigate methane is strong a warming effect add to this the fact that methane is also very short-lived within the atmosphere and breaks down to form both water vapor and co2 and it's clear that it can't compete with either in importance so what is the most important greenhouse gas well clearly that depends on what we mean by important the context in which we are asking the question and that's kind of the point of this video because when we look at complicated systems like the climate context and nuance are everything and it's far too easy to misuse a fact to support an entirely incorrect conclusion for contributing to the global greenhouse effect and maintaining global temperatures water vapor is undoubtedly the most important but for driving global warming no gas can compete with co2 that's all for today folks as always further reading and relevant sources are in the description thanks for watching and don't forget to Like comment and smash that subscribe button if you haven't already until next time goodbye you