The measurements showed that in the past half century, CO2 levels have been steadily rising at an exponential rate (Weart). This is due to growing population and the quickly-developing technologies that inevitably demand more energy, and, in the present, humanity's main source of energy is fossil fuels.
As such, finding alternative energy sources has become a very important quest in the present. Among these alternative sources of energy is Hydrogen. Hydrogen is often presented as one of the most promising alternatives for carbon-based fuels because it is the clean energy source that burns into water vapor. It is also often pointed out that Hydrogen is the most abundant element in the universe and is very abundant on earth itself in the form of water. However, switching to a Hydrogen powered economy isn't really as simple as it sounds. Although water is very abundant on Earth, it takes up a lot of energy to break it down into its hydrogen and oxygen components and package it (Zyga). There is also the risk of hydrogen leaking out from the fuel cells which contain it (Warwick et. al.). Hydrogen energy would then basically cost more and be less economical than the current energy sources. However, if switching to Hydrogen as a major energy source would have good environmental impacts, then maybe it would be worth the cost.
The product of Hydrogen combustion as opposed to, say, gasoline combustion would only be water vapor whereas for gasoline combustion, the products would include carbon dioxide which is considered to be the major cause of global warming. However, there are some who argue that water vapor, in fact, is the major greenhouse gas and is responsible for a larger portion of the greenhouse effect than carbon dioxide is. So, to find out whether hydrogen would really be a better energy source than carbon-based fuels, let us first look into the reactions involved in their combustion. For the carbon-based fuels, we'll just take octane, which is an important component of gasoline, as an example. The combustion reactions are as follows:
2 H2 + O2 2 H2O + 572 kJ (1)
2 C8H18 + 25 O2 18 H2O + 16 CO2 + 11017.8 kJ (2)
If we multiply equation (1) by 20, we get roughly the same amount of energy generated for the two reactions:
40 H2 + 20 O2 40 H2O + 11440 kJ (3)
So, to produce the same amount of energy, 16 CO2 molecules and 18 H2O molecules would be produced for the octane combustion while 40 H2O molecules would be produced for the hydrogen combustion. If water vapor is a greenhouse gas just as CO2, then it my be that switching to hydrogen as an energy source would bring about an even worse greenhouse effect than the CO2 produced by burning octane. However, there are a lot of things to be considered. Even though water vapor makes up 80% of all greenhouse gases in the atmosphere by mass, it is responsible only for 36% - 66% of the long wave absorption done by all the greenhouse gases (Schmidt). By contrast, CO2 comprises only 1.44% of all the greenhouse gases by mass, yet it absorbs 9% - 26% of the total long wave absorpt