One of the most commonly held misconceptions about the man-made global warming hypothesis is that temperatures must increase every year and evenly over the world. No one knowledgable about climate issues would seriously claim that, so it’s an obvious strawman. The question is, why do temperatures fluctuate so much and does global warming explain this? Indeed it does!
The process begins with the slight increase in CO2 in the atmosphere known to be caused by human emissions. Because CO2 traps slightly more heat, it also causes more water to evaporate. Water vapor is also a greenhouse gas, so that causes a feedback loop, in which the temperature increases further, causing more water to evaporate. In the summer months, the result is much hotter weather than you might expect from CO2 alone.
But H2O has an opposite effect in winter. As temperature drops, the increased amounts of H2O forms clouds, which block sunlight and thus cool the earth further. Winters will be even colder than one would expect, plus there would be increased precipitation, including snow.
As long as the average temperature over the course of a year at a certain place or region is below the melting point of water, then global warming actually has the paradoxical effect of causing colder winters, more snow and thus increased ice in certain places. It is where the average annual temperatures have risen above the melting point of water that we see glaciers retreating. And the hotter summers at the northern ice cap are nothing to ignore, for its melting away will still have a tragic effect on polar bears.
In the southern hemisphere, global warming has had less of an effect, and this can be explained by geography. There is far more land up north than down south. Land radiates heat, while oceans absorb it. Also, the Arctic Ocean is water surrounded by warmer land, while Antarctica is frigid land surrounded by cold oceans that insulate it from warmer regions. So it stands to reason that the Arctic Ocean will melt long before the Antarctic ice cap does, and that there may even be some increase in Antarctic ice for the reasons I explained above.
If there was no CO2, or any other greenhouse gas in our atmosphere, the average temperature on Earth would actually be below the freezing point of water, thus the oceans would be frozen over and life on land would be impossible. And if there was no H2O to form oceans and absorb CO2 from the atmosphere, then CO2 would have accumulated so greatly in the atmosphere from volcanic eruptions over billions of years that we would have experienced temperatures too high for carbon based life forms to survive, thus we would already be like Venus. The abundance of water on Earth, plus the small amount of CO2 in our atmosphere, provide the delicate balance that maintains life on Earth. But too much CO2 can be as much a problem as too little, hence our concern about how much longer it may be before we reach a tipping point in the climate change problem.
If the solar activity drops, while the CO2 levels remain high AND the H2O levels are also high, the end result is warm summers and VERY COLD WINTERS!
But when the Sun roars again, all else being the same, we will get: Mild winters and VERY HOT SUMMERS!
Although both CO2 and H2O are indeed greenhouse gases when both are in their gaseous state, in practice only CO2 is always in that state in the atmosphere. That is why CO2 is indeed the most important greenhouse gas, despite it being less prevelant than water vapor. Global warming denialists have exaggerated the greenhouse role of H2O to justify ignoring CO2. That is flat out dishonesty.
The proportions and molecular weights of the most common components of the Earth’s atmosphere are:
- Nitrogen (78%) : 28
- Oxygen (21%) : 32
- Argon (1%) : 40
- CO2 (0.039%) : 38
- H2O (0.4%) : 18
Note that! Water vapor has less than HALF the molecular weight of CO2! And that leads to some serious results.
Since nitrogen and oxygen form nearly 99% of the atmosphere, the average molecular weight of it will be between 28 and 32. CO2 is heavier than that average, while water vapor is MUCH lighter than that average. Thus water vapor will tend to rise much more than the other gases listed.
Because CO2 is lower in the atmosphere, it traps heat closer to the surface. Trapped heat causes evaporation. The H2O quickly rises and as it does, it cools. In some cases, the relative humidity of the rising H2O exceeds 100% and that results in the formation of clouds, which block and reflect sunlight. And this nullifies H2O’s greenhouse effect and it instead becomes a cooling agent, all the way down to the surface. It is common knowledge that cloudy days are cooler than clear ones. The only times the greenhouse effect of H2O is really significant is at daytime when the sky is clear, and at night when the sky is cloudy. In the latter case the clouds hold in heat that would otherwise escape when the sky is clear.
Thus this statement by ICECAP, a denialist front group, is falsified:
CO2 is the most important greenhouse gas.
Not even close. Most of the greenhouse effect is due to water vapor, which is about 100 times as abundant in the atmosphere as CO2 and thus has a much larger effect.
This is misleading. The overwhelming tendency of water vapor to rise, to form clouds, and to shield the Earth’s surface from the Sun’s rays make the reality of the issue far more complex. CO2 by nature actually has the larger effect because it NEVER forms clouds and thus can ONLY be a greenhouse gas. It operates regardless of the weather.
Of course, that will not deter denialists. They will still say, “Well, if CO2’s greenhouse effect is opposed by the cooling effects of water clouds, doesn’t that mean CO2 can’t change climate?” But that is wrong too. The skies are not always cloudy. Increasing CO2 amounts by human activities DO trap more heat, which goes into the oceans and into other bodies of water, including the Arctic Ocean. And that stored heat is why the Arctic ice cap has been melting away. That is also why we had that incredibly strong El Nino of 1998 and why we had so many devastating hurricanes a few years ago. In deserts, where there is hardly any water, the cooling effects of H2O do not apply and those areas will be even hotter and drier. And in areas where there is already plenty of rain, there will indeed be more rain, resulting in flooding in certain regions.
In short, the denialism of global warming/climate change is based entirely on ignorance, dishonesty, and hypocrisy. We need to debunk and do away with it for good!