The Global Warming Debate
This artical from www.theglobalwarmingdebate.com is a very comprehensive debate about global warming, with evidence pointing in both directions. The reader is encouraged to make up their own mind given the evidence.
Global Warming is a reality, and human contributions are significant.
I will do my best to justify this, although it will likely remain a work in progress for some time, at least until I iron it out a bit. The history of temperature on our earth is the fuel for a lot of debate, but if you take a close look at what the figures are actually saying you will quickly conclude that there is nothing in there to suggest that humans can't affect the climate. In fact, there are many warning signs of how bad things can really get. I will divide this discussion into Long Global History (Hundreds of millions of years), Recent Global History (Hundreds of thousands of years), and Recent Human History (1000AD-Present). I will try to address each argument against the idea of Anthropological Global Warming individually.
Long Global Temperature History
Something I hear a lot is that global concentrations of CO2 are lower now than they were at other times of earth's history, and that the world's temperature is also lower now than it has been at other stages of earth history. To use this as an argument against the idea of Anthropological Global Warming is not possible without misleading the reader.
graphic representation of global temperature and CO2 concentrations for the past 600 million years (source: CO2 Earth History)
Although the accuracy of this graph is disputed, I will use it here as it is an image often cited and referred to by global warming deniers. If you look at the present day, you will see that temperatures are actually quite low. Life on this planet has evolved to survive in these conditions, and even small deviations can be irrevocably destructive. The higher peaks, such as those present during most of the past 500 million years, show us how hot the atmosphere can make our earth. This graph strongly alludes that CO2 concentrations are however not strongly related: A trough in CO2 concentrations is always accompanied by a temperature dip, but not vice-versa. I cannot speak for the accuracy of the above graph, since I was unable to find any reliable source for it. A verifiable representation of temperature histories on a similar scale can however be found in the nature journal:
Comparison of CO2 calculated by GEOCARBSULF (brown range, red, blue and green lines) to an independent CO2 record from proxies (black/white). For a detailed description please refer to the original paper by Royer et. al (2007).
This graph tells a somewhat different story, showing a strong correlation between temperature and CO2 levels for the past half a billion years. At the very least this should teach you to be wary of anyone who claims to tell you that CO2 did not relate to temperature in the past.
Recent Global Temperature History
In June 1999, researchers recovered ice core data from the "Vostok" site in the Antarctic regions. The results were published by Petit et al in Nature. By recovering the gas concentrations within the gas layers, the researchers were able to obtain detailed information about greenhouse gas concentrations throughout the past 400,000 years. By plotting this information against the estimates for global temperatures over the same period, the following can be obtained:
CO2 concentrations against temperature for the past 400,000 years (source: Petit et al)
What should be noted about this graph, is that it says absolutely nothing about the cause for these changes. The graph seems to indicate that CO2 concentration changes are preceded by temperature changes. There is some truth to this, although the actual time lag is subject to dispute since the air trapped inside the vostock ice records is younger than the ice itself (New Scientist (2007)). Even if temperature did in fact lag behind CO2 variations in the past, it would be a logical fallacy to conclude from this that CO2 concentrations are not the driving force for temperature variations today, since the mechanisms are distinctly different to those that have occurred during the past 400,000 years (one needs only to look at the above graph to notice the sharp and unprecedented climb in CO2 concentrations during the last century to verify this). This is an important logical distinction, and many people will try to trick people in missing this link in order to use graphs like this to suggest that CO2 concentrations cannot be a driver for temperature changes. This is simply not the case, and one should always be weary of arguments which use the lack of something occurring in the past, to be evidence to suggest that it cannot happen in the future. This is especially true when the present situation is unprecedented, as is the case to day: If you take a closer look at the CO2 concentrations at the end of the graph (ie. today), you will notice a sharp peak. CO2 concentrations are today at about 380ppm.
This is almost 100ppm higher than the highest peak in the past 400,000 years. Of course, there were times several million years ago where CO2 concentrations were higher than 1000ppm, but at that time the world was an inferno, and Dinausaurs roamed the earth. If we were to revert the climate to that state, all life as we know it would end. So please don't let anyone tell you that because the earth once experienced higher CO2 levels, that it would be ok for this to happen again. It's simply not true.
Recent Global Temperature History
Most of the "global warming is a load of garbage" arguments take their evidence from this period as far I can tell. During the past 1000 years, 2 major events climatic events of interest have occurred:
1. The Medieval Warming Period
2. The Cooling period during the 1970s and 80s
I have already discussed the cooling period during the 70s and 80s in some details, so I'll address the Medieval Warming Period here. There is a traditional notion that during the 500 years before and after the year 1000AD (generally accepted as being between 800-1300AD), the earth went through a "warm" period. Below is a graph outlining temperature records for the northern hemisphere during this period:
Northern Hemisphere temperatures through the "Medieval warming" period (source: Wikimedia commons)
Ignoring the vastly different warming patterns observed between the medieval warming period and today (which alone indicates different drivers for the warming), one needs to consider what the science says about the causes for the warming before making the assumption that the same non-human forces are at work today. There are 2 main respected schools of thought on this. The first is outlined in Parker (1999), suggesting that sunspot activity was the cause of this warming. The second view, which is one that seems to have the most scientific credence, is a view echoed by the IPCC in the IPCC Third Assessment Report, claiming that the medieval warming period was isolated to the northern hemisphere, and that temperatures in the southern hemisphere actually went below the average.Mann et. al (2009) supported this argument by stating "The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally".
However, since it's the IPCC's snafus that have me needing to justify their work, I suppose it would be a little hypocritical to just take their word for it. So let's assume that Parker was correct, and that it is indeed sunspots that were at work. This brings me to the 2nd part of my article.
Sunspots and the 20th century
A recent film titled The Great Global Warming Swindle has popularised an article by Christensen et. al (1991), which stated that it might in fact be sunspot cycle times which are responsible for global variations in temperature. This theory is quite compelling in light of th
Solar cycle length, plotted against global temperature (source: Extracts from Ofcom Complaint, by Category: Falsification/Manipulation)
I would love to go into why everything said in The Global Warming Swindle was a big load, but unfortunately I can't be bothered. I'll just stick with their flagship argument. Aside from the fact that the predictions made by this paper were dismissed as invalid 3 years before the release of the Great Global Warming Swindle (see Damon and Laut (2004)), one only has to look at the data more closely to realise something very surprising. Let's look at the same graph extended over a longer time period:
Solar irradiance, plotted against global temperature (source: The Solar Cycle and Global Warming)
What we now begin to see, is that there was a strong correlation between solar irradiation, up until the 1970s. After that, it blatantly stopped. The fact this was simply ignored in the Global Warming Swindle is, ofcourse, pathetic journalism. But to answer the question of what did actually cause the correlation to end, let's look at CO2 emissions for that period:
CO2 emissions against global temperature (source: Evidence that CO2 is Cause)
By looking at these graphs, and considering the fact that CO2 is known to increase the amount of heat retained in the atmosphere, one can't help but arrive at one simple conclusion, one that is supported by every single scientifically obtained piece of information I just presented:
Solar radiation may have been a significant cause for climatic variation in the past, but the overwhelming increase in CO2 toppled that effect during the latter half of the 20th century.
As of 1970, we are in control.