CO2 the basic facts
The amount of carbon dioxide (CO2) in the atmosphere has varied a great deal over time. Sometimes it has been lower than now and sometimes it has been much higher than now. It is also true that it has been both a lot hotter and lot colder at various time in the past. There is no evidence that CO2 has caused the temperature to change in the past. All studies of temperature and CO2 levels in the past show that it is the temperature changing which changes the CO2 level and not the other way round – see this short video clip here.
Before industrialisation the natural level of CO2 in the air was about 270 parts per million. It is now about 386 parts per million. This means that humans have added about 116 parts per million.
CO2 is a gas that makes up a tiny, tiny part of the atmosphere. To put the figures above in a different way: There used to be about 27 molecules of CO2 for every 100,000 molecules of air and now there are roughly 39 molecules of CO2 for very 100,000 molecules of air. So humans had added about 12 molecules of CO2 for every 100,000 molecules of air.
Let’s picture this in another way to really get an idea of the scale of CO2 compared to the total atmosphere. The Eiffel Tower in Paris is 324 metres high (1063ft). If the hight of the Eiffel Tower represented the total size of the atmosphere then the natural level of CO2 would be 8.75 centimetres of that hight (3.4 inches) and the amount added by humans up until today would be an extra 3.76 centimetres (1.5 inches)
Here is a short video which uses grains of rice to illustrate how small the CO2 component of the atmosphere is.
Humans are adding extra CO2 to the atmosphere at the rate of about 2 parts per million every year. Some people think that CO2 is rising dramatically. This is probably because of graphs like the one below.
However the graph above could be considered dishonest, because the y-axis starts at 290 instead of zero. This misleads the reader into thinking that CO2 levels have undergone a huge increase. When the data are plotted honestly, with the y axis starting at zero, the true scope of the change becomes clear as shown in the graph below.
The trace levels of CO2 in the atmosphere are not poisonous or directly damaging in any way but CO2 in the air does has two effects, one good and one that it is claimed is bad.
Lets start with the good. CO2 is plant food. It is generally accepted that the extra CO2 pumped into the air (as a byproduct of our improvements to our civilisation) has increased global plant growth by about 15% in the last century. That means about 15% extra forest growth and about 15% more food for humans. This is a good thing.
CO2 is also a greenhouse gas and this it is claimed is a bad thing. The earth receives incoming heat from the sun and it radiates away heat into space. Greenhouse gases are substances in the atmosphere that reduce the mount of heat radiated way from the earth so more heat is kept on the planet. There are several greenhouses gases of which water vapour (in the form of clouds) is by far the most important. CO2 is also a greenhouse gas but it is very much less significant than water vapour.
What does a greenhouse gas mean? To put it simply, the energy that hits the earth from the sun is shortwave radiation and as it passes down through the atmosphere to hit the earths surface it is not absorbed by the greenhouse gases it passes through. At the surface, it is absorbed and then re-radiated at longer wavelengths (as “heat”), and now some of this heat radiation is at just the right wave length to be absorbed by the carbon dioxide and water vapour in the air as it passes up towards space. This portion of the energy bouncing back towards space is absorbed by the CO2 gases on its way up. If there is more CO2 in the air it will cause some of this outgoing energy to be absorbed at a slightly lower altitude than before. Some of this energy will be absorbed and re-emitted by the carbon dioxide molecules. So more CO2 means that outgoing heat is absorbed at a lower altitude and this means a bit more heat is added back to the atmosphere. The question is, is the amount of warming enough to be significant?
As explained above the heat bouncing back into space has a different wave length to the heat coming in, But only a portion of these new wavelengths are absorbed by the CO2, so CO2 can only ever absorb a narrow band of the heat bouncing back out so there is an upper limit to how much heat CO2 can keep in. Even if the atmosphere was all CO2 lots of the heat would still get out and the temperature would only increase to a certain point.
It is easy to get the wrong impression and to think, for example, that CO2 is cumulatively adding more and more heat to the atmosphere in some sort of runaway process. A good way to think about it is to imagine an aluminium pot that is full of water. If you place that pot in direct hot sunlight the water will get warmer. But no matter how long you leave the pot in the sunlight, you could do it for hours and hours, the pot of water would never boil. If you then painted the pot black and put it back in the sunlight the water would get a bit hotter than before it was painted but the water would still not boil. Without stretching this metaphor too far you can think of the black paint on our imaginary pot as the CO2 – pushing the temperature up a bit but only so far.
Before manmade emissions added to the CO2 there was already a level of CO2 in the air, a level which is the natural level for this particular period of earth’s history. It is generally accepted that this natural level of carbon dioxide in the atmosphere was already high enough to absorb virtually all the infrared radiation that was just the right wavelength to be absorbed by the CO2.
Because most of the energy which CO2 can absorb was already being absorbed before the CO2 level was increased any extra CO2 can only absorb a small extra bit of energy. Even if the atmosphere were heavily laden with carbon dioxide, it would still only cause an incremental increase in the amount of infrared absorption over current levels and temperatures would only go up incrementally. Doubling carbon dioxide would not double the amount of global warming. In fact, the effect of carbon dioxide is roughly logarithmic. Each time carbon dioxide is doubled, the increase in temperature is the same as the previous increase. The reason for this is that, eventually, all the long-wave radiation that can be absorbed has already been absorbed. It would be analogous to closing more and more shades over the windows of your house on a sunny day — it soon reaches the point where doubling the number of shades can’t make it any darker.
Another way of looking at it is by thinking of adding blankets to your bed on a cold night: if you have no blankets, adding one will have a big effect. If you have a thousand blankets, adding another thousand will have an unmeasurably small effect.
Here is what do we know about the basic physics of this CO2 greenhouse warming. It is reliably estimated that the current elevated levels of CO2 has added about 2 watts of heat per square meter across the globe above the natural level. In order to picture this think of a square meter of the ground and then think of the whole column of air sitting above that square meter stretching all the way up into space miles above us. Then think about adding a 30th of a sixty watt light bulb to that column of air. Its not a huge amount of energy. For various reasons most of the heating from the CO2 greenhouse effect is expected to take place in the upper atmosphere. Satellite measurements of upper atmosphere temperatures do not show much warming in the upper atmosphere in recent decades, the heating that has taken place appears to be near the surface where you would not expect the extra CO2 to have the most effect so the satellite data is at odds with the CO2 warming effect hypothesis.
It is claimed that this heating from CO2 has pushed general global temperature up and will continue to do so in the future in a dangerous way. Nobody knows for sure whether the fairly gentle warming of 0.07℃ that has occurred in the last 100 years is the result of CO2 warming or natural warming or a mixture of both.
The natural level of CO2 before we started adding extra CO2 was about 280 part per million. Since the industrial revolution we have added another 100 part per million. Even the climate alarmists only claim that this has led to an increase of about 0.7℃.
Because the effect of extra CO2 is logarithmic in order to add another 0.7℃ in temperature we would have to add another 200 parts per million taking the total up to 480. This is not expected to happen until near the end of this century. This would mean that the total CO2 temperature increase due to CO2 increases from preindustrial times right up to the end of the 21st century would be 1.4℃ and we have had half that increase already. To add an additional 0.7℃ on top of that we would have to add another 400 parts per million taking the total up 880, the next 0.7℃ would take an extra 800 parts per million taking the total up to 1680 parts per million and so on.
So even if we accept that all the warming of the last centre is solely the result of manmade emissions of CO2 then we are only likely to only see a further rise of about 0.7℃ in the next 100 years. This is a pretty trivial figure and on its own should not cause humans, other species or the planet too much of a problem.
The climate alarmists use computer models to project what might happen to the climate in the future. These climate models produce wildly different different results and they fail to predict climate changes like the cessation of warming that has happened over the last decade so one should really consider them very inaccurate. Most of these models propose that the small 0.7℃ warming that CO2 might cause over the next 100 years will trigger various feedback mechanisms that will push the temperature even higher. The models used to estimate these proposed feedback mechanisms are very speculative and almost certainly very inaccurate. Click here to see a video lecture about some empirical work that was done to test some of these feedback models. Usually climate alarmists will pick those models with the most extreme predictions and publicise them in a sensational way in order to increase alarm.