Is Global Warming Real?

Coming back to the video I posted 2 posts back about The Great Global Warming Swindle, I want to discuss about the extent of anthropogenic effects on this idea of global warming. Taken alone, global warming shouldn't be such a big deal. After all, global warming has happened in the past during the medieval warm period and even earlier during the Late Glacial Maximum (Tardiglacial) that occurred 13,000-10,000 years ago or even further back during the Paleocene–Eocene Thermal Maximum that occurred 55.8mya. Assuming the cyclical nature of temperature changes between glacial and interglacial periods, the current climatic change is arguably the result of natural climatic fluctuations that have been occuring.

This image shows palaeotemperature graphs stitched together to form one graph from various sources that can be accessed here: Palaeotemperature graphs Sure, it is a wikipedia post, but I do think it is generally a good starting point to understand topics of interest. According to this stitchwork (accurate or not), we realise that temperature fluctuations have occurred between geological time periods, and within time periods. It is therefore justified that people believe that we are merely entering a warm phase in the holocene and there is nothing to worry about.

This is exactly the argument presented in the video. Global warming has always been occurring, and to make it into an anthropogenic problem is the result of political campaigning, ignorance and lack of solid scientific evidence. They propose that there are other more important effects for global warming such as volcanic activity that produces massive amounts of CO2, cloud cover and solar effects. They claim in the video that indeed there is a connection between CO2 and temperature, but Al Gore has got it the "wrong way round" (this video is clearly a response to Al Gore's inconvenient truth). Ian D. Clark, a professor in the Department of Earth Sciences at the University of Ottawa, argued that in fact warming increases carbon dioxide and that there is a time lag of 800 years between carbon dioxide levels and temperature, in the graph here screencaptured from the video.

Climate science is most certainly an uncertain science.

In 1975, Broecker S.W. wrote a commentary titled "Are we on the Brink of Pronounced Global Warming" that addressed the trend of climatic cooling in the post war period. If you have no idea what I am talking about, here is another graph from the video to show temperature changes in recent times.

In this graph, we see that the documentary argues that we have had a cooling period between 1940 - 1975, when economic growth was the greatest, hence temperature changes should not be attributed to humans. Broecker argues, however, that this cooling period merely hides the huge increases in temperature that is to follow if we continue once the cooling effect "bottoms out". CO2 would then become the driving force behind temperature increases. Trying to include both natural and anthropogenic factors into temperature change, he produced the following data:

This is based on the assumption that "50% of all CO2 generated by burning chemical fuels has in the past and will in the future remain in the atmosphere" (Broecker 1975, 462), there is a growth rate of 4.5% per year of fuel consumption, and that a 10% increase in CO2 increases global temperature by 0.3dC. His main arguement is that the warming trend of CO2 has been countered by a cooling trend which was soon ending, we would then be faced with a CO2 induced warming trend that would bring warming beyond the range experienced during the last 1000 years, which according to the data by Crowley (2000), proves to be the case (although in his graph he did not attribute the rise to co2)

So we can see how the same point made by 2 different sets of scientists can be interpreted in different ways. While both acknowledge the natural variance of climate over time, those in the video believe the warming trend to be part of yet another natural variance. While Broecker does not deny this, he believes the larger than usual rise TO COME would be largely attributed to CO2 emissions.

Lean and Rind (2008) agrees with this point of view as well. But before we get to that, we shall review what he feels about natural causes for global warming. He believes that volcanic cooling, solar activity and el nino as possible natural causes for climate change. For example the "1997 ‘‘super’’ ElNino the globe warmed 0.23 ± 0.01 from June to November". Similarly, the volcanic eruption of Mount Pinatubo produced gobal cooling from November 1991 to September 1992 of 0.25 ± 0.02 K. Solar activity, one of the perceived main causes of global warming in the video, is detected in the global historical surface temperature record, for example, producing a peak monthly increase of 0.17 ± 0.01 K from April 1996 (solar minimum) to February 2002 (solar maximum). According to Scafetta and West (2006), it contributes to 65% of surface warming in the past 100 years.

While Lean and Rind does believe that natural factors exist, and has provided data to support this view of the importance of natural factors, he often feels that such data has been exaggerated, which is not surprising since he belongs to the camp that believes that anthropogenic factors are to blame. He feels that solar induced warming contributed 10% to warming in the past 100 years, not 65% and that "Linear trends in temperature attributed to ENSO, volcanic aerosols and solar irradiance over the past
118 years are, respectively, 0.002, 0.001 and 0.007 K per decade" and hence cannot explain the long term warming trend that we are seeing today. His use of the phrase "anthropogenic changes" however fails to describe what specific anthropogenic factor he refers to, only vaguely defining it as "anthropogenic gases". However, the key point of this research, and a key take away that any scientific enquiry should take is as follows:

"To properly quantify their amplitudes, the natural and anthropogenic changes must be accounted for simultaneously when analyzing the surface temperature anomalies, since neglecting the influence of one can overestimate the influence of another."

Good advice indeed. I like how many of the journal articles I have read are able to present both sides of the picture when explaining global climate change. I mean, I appreciate Al Gore for spurring us into action and The Global Warming Swindle for providing an alternative view, but they are not the complete picture (ignoring the obvious people bashing tendencies). But then again, perhaps we will never have a complete picture of climate change, and opinions are what matters in such an issue.

Let the great Climate debate continue.

References:
Crowley, T.J.(2000) "Causes of Climate Change Over the Past 1000 Years", Science, 289, 270-277

Lean, J.L and Rind, D.H. (2008) "How natural and anthropogenic influences alter global and regional
surface temperatures: 1889 to 2006", Geophysical Research Letters, 35

Broecker, W.S. (1975) "Are we on the Brink of Pronounced Global Warming?", Science, 189, 4201, 460-463

Wikipedia Temperature Record of the Past 1000 years

Geologic Timescale