In 2006 The An Inconvenient Truth
In 2006, the An Inconvenient Truth was released to convince the public about human influence on recent climate change and its terrifying consequences. And the year after that, another documentary, the Great Global Warming Swindle, was released which hold the opposite viewpoint toward carbon dioxide-induced warming and criticized the An Inconvenient Truth.
Before criticising the arguments and the weaknesses of the two documentaries, 3 most convincing evidence or arguments would be discussed below.
Firstly, the An Inconvenient Truth shows two graphs of 1000 years of carbon dioxide and global warming which the two graphs show matching each other. The temperature used in the graph was obtained from Northern Hemisphere. Both the carbon dioxide and temperature started changes since around the 1800s. With another graph put together the carbon dioxide level and temperature over the last 650000, the changes of the two fit perfectly together. The data shown are from the study done by the Physics Institute at the University of Bern and the European Project for Ice Coring in Antarctica. the past 650000 years, the carbon dioxide concentration had never gone above 300ppm. And the current carbon dioxide level is way above 300ppm and the natural cycle. These supported Al Gore’s argument that temperature is raising when the carbon dioxide concentration is increasing. And he explained carbon dioxide has trapped heat inside the Earth as a greenhouse gas to drive the increasing global temperature. Projection is shown in the documentary which the future carbon dioxide level in the next 50 years would be almost double today’s concentration. Therefore, Al Gore concluded that the carbon dioxide is matched with the temperature change.
Secondly, another graph of the northern hemisphere temperature over the last 1000 years was shown in the documentary raised the point that the recent warming is incomparable to the past warming period. The red part of the curve represents the warming period which included the Medieval Warm Period in around 950-1250. The recent warming is much more significant than that over the last 1000 years.
Lastly, Al Gore gave examples of glacial melting worldwide, including Mount Kilimanjaro, Glacier National Park, Columbia Glacier, Himalayas, glaciers along the Alps and Peru in South America, to prove the warming is in a global scale. For Mount Kilimanjaro, he showed a photograph more than 30 years ago and combined it with the current situation of the same place. It is stated that within a decade there will be no more snow in Kilimanjaro. Same for Glacier National Park, within 15 years there will be no more ice found in the park. Another example used, the Columbia Glacier is retreating every single year. Never the less, huge impact will be caused due to the disappearance of the glacier in Himalaya. Within the next 50 years, 40% of the world population will lose their drinking water source from rivers and spring systems supported by meltwater from Himalaya and facing a very serious water shortage. With the dramatic photographs of glaciers before and after the retreat shown in the documentary, the presence and consequence of global warming are convincingly shown to the audiences.
The Great Global Warming Swindle is produced after the release of Al Gore’s An Inconvenient Truth, challenging Al Gore and IPCC statement on anthropogenic carbon dioxide as the cause of global warming.
From the Great Global Warming Swindle, one of the most convincing argument is that the trend of atmospheric carbon dioxide concentration is actually lag behind the change in temperature. During the Post-war economic boom in 1940, global industrial activities emerged rapidly. However, from the temperature record, the temperature started rising since the mid 19th century which is far before the invention of cars and planes. And the temperature change in the Post-war economic boom actually shows a cooling signal.
Secondly, the Great Global Warming Swindle also argued that the recent warming is a natural fluctuation on Earth climate which is a cyclical phenomenon. Earth climate is changing throughout Earth’s history, and there are different time period having much cooler and warmer temperature than today. For example, Medieval Warm Period and Holocene Maximum have significantly higher temperature compared to the current temperature.
Thirdly, the Great Global Warming Swindle mentioned that highest warming rate should be observed in the middle of troposphere if the Earth is under global warming. Under the greenhouse effect, greenhouse gas traps the escaping heat in the Earth’s troposphere a few miles above the surface. However, from both satellite data, the maximum temperature is found near the Earth’s surface instead of the middle of the troposphere.
Now will move on to discuss some missing elements in the conclusions of the documentaries and the weaknesses in their arguments.
Firstly, in the Inconvenient Truth, one of the weaknesses of their argument is they only focus one driving force on climate change. Besides carbon forcing, there are different forcing for example volcanic forcing and solar forcing. And there are warm periods in the past which has low carbon dioxide level, for example, the Warm Miocene Climate. The documentary failed to explain the causing for the warming during those time. And although solar forcing is following a natural cycle following the Milankovitch cycles and the sunspot cycle, and the uncertainties on estimating volcanic forcing over last 1000 years that mentioned in the IPCC report, the possibilities of recent warming is due to the effect of solar or volcanic forcing should not be excluded. Al Gore statement on carbon dioxide driving global warming was not wrong, only it is true over the last 1000 years. From IPCC5, it is claimed that anthropogenic drivers are extremely likely to cause warming since the mid-20th century. Carbon dioxide is the most contributing among all greenhouse gases. And the IPCC has a high confidence to say that the anthropogenic effect is much larger than the effect of solar activity on recent warming. It would be correct to say the recent temperature increase is due to increasing carbon dioxide emission. The historical temperature changes before the increasing anthropogenic carbon dioxide since the industrial revolution is mainly driven by the changes in solar irradiance. (IPCC) Therefore, other forcing should also be included in the documentary to prevent it from being one-sided.
Secondly, as mentioned above, one of the more convincing graphs was the one showing an exact fit between increasing carbon dioxide and increasing global temperature. The graph used shows the carbon dioxide level and temperature increase with one another. In fact, the graph should have been smoothened which can more easily show the matching of the two trends. And the relationship of the carbon dioxide and temperature should have changed over time instead of perfectly matching from each other. When looking closer at the shorter timescale of changes, argument is found based on the relationship between the two variables. The Great Global Warming had challenged that instead of carbon dioxide leading the temperature change, historical records show that temperature actually rises before the increasing carbon dioxide level. The graph (figure 1) showing carbon dioxide and temperature change based on a study done by Nicolas Caillon and his colleagues in 2003. The study suggested there is an 800 Â± 200 year lag in around 240000 years ago during the Antarctic deglacial warming (figure 2). This can be explained by the releasing of carbon dioxide from the ocean as the ocean temperature increases. And the released carbon dioxide would play a positive feedback which further increases the temperature. Human-induced carbon dioxide only occurred in the last 50 years which other forcings might have driven the previous temperature change. Therefore, the carbon dioxide concentration is still the driving force to the recent temperature change which the previous warming could be due to other forcings such as solar activities and the temperature change has an effect to increase carbon dioxide concentration. The missing element in the conclusion would be the effect of the changing insolation pattern on temperature change in the long timescale. And smaller timescale of carbon dioxide and temperature changes should be also shown in the documentary, especially during the recent warming, to show current warming is led by the changing carbon dioxide concentration.
Another weakness of Al Gore’s argument is the uncertainties on carbon dioxide and temperature
Some of the argument points are not scientific
e.g. Hurricane (not even correct)
Great Global Swindle
Moving on to the Great Global Swindle. At the beginning of the documentary, it mentioned that carbon dioxide contributed only a small part of the atmosphere which should be considered as a relatively minor greenhouse gas. It quoted that carbon dioxide is only 0.054% of all gases in the atmosphere, and the portion of anthropogenic carbon dioxide would be a much smaller part of the atmosphere. This statement is considered as misleading as other factors such as heat-trapping potential and resistance time should also be taken into consideration.
From the IPCC5, radiative forcing of different climate forcing is calculated which means the net changes in the amount of energy to reach Earth’s surface contributed by each forcing. Some other gases are having higher heat-trapping potential such as methane, however, they have a lower atmospheric concentration. And although water vapour is the most abundant greenhouse gas in the atmosphere, it has a short atmospheric residence time for about 10 days. And carbon dioxide is a more stable gas which stays in the atmosphere for a long time. According to the radiative forcing, overall, carbon dioxide has the highest radiative forcing among all anthropogenic forcing.
Second, one of the criticism the documentary on the relationship between carbon dioxide and the temperature is the cooling trend during the Post-war economic boom. The temperature increase when before the active industrial activities but fell when economic boom. However, the documentary failed to address other influential factors on climate change. The warming before the production of human-induced greenhouse could be due to the solar activities, whereas the cooling during development can be explained by the cooling effect of pollutants, such as insolation reflection by pollutants (e.g. sulphate aerosol).
(3) any additional comments you think are important to lead to the two quite controversial views on the global warming issue
The main reason for the controversial views of the two documentaries on the global warming issue is that the temperature used by the two documentaries are obtained from different sources. Both the two documentaries used temperature records over the past 1000 years which the temperature over the past 100 years is almost the same. However, the temperature during the Medieval Warm Period in 1250AD to 950 AD shows a big difference. The datasets used by the An Inconvenient Truth and The Great Global Warming Swindle are from the ice core in Antarctica and Arctic respectively.
In the An Inconvenient Truth, the overall temperature trend reconstructed from Arctic ice core data over the last 1000 years shows a Hockey Stick shape. The temperature first started with gradually cooling and followed by the sudden warming. The warming signal is found in around 1100 to 1400 which refers to the Medieval Warm Period. But those warming is much insignificant when comparing to the current situation, temperature nowadays is significantly higher than the Medieval Warm Period. The temperature and carbon dioxide concentration record from Antarctica ice core data can be reconstructed back to 650000 years. The carbon dioxide has never gone above 300 ppm in the past. And the temperature and carbon dioxide concentration trend fit together closely which shows more atmospheric carbon dioxide concentration is followed by the increase in temperature.
In the Great Global Warming Swindle, the past temperature record is reconstructed from Arctic-wide Surface temperature. And from the graph showed in the documentary, the temperature increased from 1900 to 1940, then dropped from 1940 to 1970 followed by temperature increase till now. The current temperature is similar to that in the 1940s which the recent warming is not significant. And the curve of temperature change fit with the solar activities curve, the documentary then conclude the major influence of the recent warming is due to the natural fluctuation of solar activities. However, from another scientific research (citation Fyfe et al, 2013), although ups and downs of the temperature graph based on Arctic-wide surface temperature are similar to that in the documentary, the recent warming is much higher than the warming in the 1940s. The graph used in the documentary is considered as a bit misleading.