Thursday, March 3, 2011

Six Minutes to Midnight - Part 5

Modern Climatologists

We pick up the story of climatology in the late 1930’s, a young steam engineer, Guy Stewart Callendar, began to study the climate in his spare time. It was known at this time that the average global temperature was slightly raised compared to the earliest records available. So as an inquisitive man he collected all the old data pertaining to carbon dioxide and temperature measurements. From his observations he noted a rise in carbon dioxide levels over the period of the measurements. He surmised that this trend was responsible for the temperature change. From this he calculated a possible rise of 2 K for the average global temperature with a doubling of carbon dioxide. His conclusion met with little acceptance. Many had at that time dismissed the data collected in the 19th century. The data recording was too variable as even a change in wind direction would drastically change your carbon dioxide recording.

To counter Callendar’s theory many used the theory that the oceans act as a large sink for carbon dioxide. Carbon dioxide can readily dissolve in water and as such the ocean can act as a vast store of this gas. Callendar countered this argument with the assumption that the ocean could only hold a certain amount within its upper layers and quickly became saturated. He theorized that it would take hundreds of years for the ocean to soak up the excess carbon dioxide.

Another argument was that adding carbon dioxide would have no effect. In a simple laboratory experiment it can be seen that a cylinder of carbon dioxide absorbed a certain amount of heat and even if you double or even tripled the concentration of the gas the heat absorbed changed by a negligible amount. But Callender correctly argued that this experiment did not account for different bands of gas at various altitudes in the upper atmosphere which were also at different atmospheric pressures. Even in the growing face of criticism, Callender never backed down and continued to counter any arguments the sceptics put forward. The one saving grace of Callender work is that it elevated global warming from some footnote in history to a current research topic.

As science entered the 1940’s there was a significant push to try and develop a more rigorous approach to climate research. This new impetus was fuelled by the Second World War and the subsequent Cold War. Various technologies were greatly advanced during this time period as the nation who was more scientifically advanced had a major advantage. Metrology and meteorology saw significant investment. Metrology dealt with taking measurements and meteorology dealt with weather forecasting. It was vital to aviation and planning military operations that the military knew how the weather would change in a certain time frame. The investment in more innovative measurement devices lead to better instruments which allowed scientists a more accurate way to monitor the health of the Earth.

In the aviation industry it was important that they knew exactly how the upper atmosphere reacted to different climatic circumstances. Also if a nation could somehow influence the weather they could use a form of climatic warfare against a potential enemy. From all this new research the old carbon dioxide data was revisited. Instead of seeing the absorption of infrared radiation as sea level pressures, scientists began to analyse carbon dioxide absorption at various pressures and concentrations. When they looked at the data they were shocked to see that adding more carbon dioxide at these altitudes greatly affect the heat retention of the Earth. In 1955 it was concluded that adding more carbon dioxide to the atmosphere would warm the planet up, this work was carried out by Gilbert Plass (1920-2002). Plass, from a series of calculations, worked out that a doubling of carbon dioxide in the atmosphere would yield a 3.6 K increase in global average temperatures and a temperature increase of 1 K over the pre-industrial temperatures by the year 2000. From current IPCC data the estimate for a doubling of carbon dioxide is 2-4.6 K and the increase in temperature to the year 2000 is 0.7 K.

The argument from the critics at this time was the ocean would soak up the excess and that we were jumping to conclusions and we should adopt a wait and see approach. Early data in the 1950’s showed that on average a carbon dioxide molecule lasted about 10 years in the air before it was captured in some other chemical process, e.g dissolved in water or reacted with another compound.

To answer these critics Roger Revelle (1909-1991) and Hans Suess (1909-1993) set about to answer the question of how much the oceans could absorb and at what rate they could scrub carbon dioxide out of the atmosphere. Revelle was the director of the Scripps Institute of Oceanography and Suess was a physical chemist who specialised in radiocarbon dating research.  Between the two of them they published their findings in 1957. In this paper it was discovered that the ocean did not offer a vast storage potential for carbon dioxide. What they did in fact find was that the ocean returned much of what it absorbed. This meant the ocean would not act a sink for all the human added (anthropogenic) carbon dioxide.

Here for the first time was the evidence that human activities could cause a global change in the climate. Armed with this evidence it was critical that we get an understanding of exactly how much carbon dioxide was in the atmosphere and at what rate it is increasing. Revelle was not only a gifted scientist but he surrounded himself with some of the best people in the field. To answer this vital question he turned to a geochemist.

In 1956 Charles David Keeling (1928-2005) was appointed to the Scripps Institute to head up research into the levels of carbon dioxide in the atmosphere. Keeling was tasked with collecting climatic data in the Antarctic and on Hawaiian Islands. At his base on the Mauna Lao volcano, Keeling began to collect data on the levels of carbon dioxide in the atmosphere. As he gathered data over the subsequent years a very ominous and disturbing picture began to emerge. 


In the figure above the Keeling curve can be seen. This graph has become synonymous with climate change and will in time become an iconic image of 20th&21st century civilisation. As can be seen there is a year on year increase in the carbon dioxide levels. The saw tooth pattern is a result of seasonal changes in vegetation, during the growing seasons (spring & summer) plants absorb carbon dioxide and during the subsequent reduction in plant life in the autumn and winter months plants release carbon dioxide back as they die off.

This data was a great shock to scientists who realised what this meant; we could potentially cause an enhanced greenhouse effect. In an article in Scientific American in 1959 Plass outlined that as human activity continues to add to the carbon dioxide in the atmosphere there will be a average global temperature increase of 3 K by the beginning of the 21st century.
In this figure is a copy of the first page of that article, this begs the question why weren’t the alarm bells ringing?

One set of data that I haven’t mentioned yet was the global mean temperature data. At this time accurate mean temperatures were being gathered. This data showed a small cooling effect. Even though most of the scientific papers on this subject hinted that an increase greenhouse effect was incoming media picked up on a few minor papers which predicted a global cooling. And so in the media eyes there was no need to worry and that the extra carbon dioxide in the atmosphere would not have any true effect.

Climate change fell away from the public consciousness until the mean temperature data took the sudden turn that had been predicted years earlier. James Hansen (b.1941), who worked for NASA, was a climatologist. He studied Venus and its own runaway greenhouse effect. In 1980 he turned his attention to the mean global temperature measurements. Using new mathematical models they were able to correct and update the global temperatures dating back to 1880. Their data did indeed show than the period over 1950-1970 showed a mild cooling and plateau. However as they collected more data each year a disturbing trend began to develop. In 1985 they published their data.

The data showed that the last three years were the hottest on record. As each year was collected this trend continued and even began to accelerate. This trend was independently verified by a British team. By 1987 the evidence was clear we were in a global warming scenario.



In the figure above is the collected data for the global temperature changes in both hemispheres and the global mean. It shows that all the hottest years over the last 130 years have all fallen with the last 15 years. This in conjunction with the carbon dioxide levels gives the clearest indication yet that there is a correlation between temperature and carbon dioxide (see below).




Climate change is a very emotive subject and has become a political battleground over the last number of years. Various documentaries have highlighted the threat posed by global warming. This campaign has also faced many critics who try to use various methods to attack certain scientists and claim that data has being skewed in favour of showing favourable data to support their results. One of the modern day climatologists which has faced the most criticism about this issue is Michael Mann (b.1965). Mann developed several techniques to help estimate the mean global temperatures through analysing ice core data. From extensive work he was able to trace global temperature trends over a far greater period than was previously possible.
  
This work led to a now famous graph which is now commonly referred to as the “hockey stick graph” which has polarised opinion (see below).



It shows a very obvious trend which is undeniable. We are at the hottest period in recent human history. The advent of the computer age has given us the capability to model the climate. With ever more accurate models and more powerful computers we are getting more accurate data. All current models tend to agree that we are heading for a period of increased warming.  It is now an inescapable fact that global warming is a real and present danger.


Epilogue

Global warming is a highly emotive subject for many reasons; it has environmental, political, social and economic concerns at its heart. Current predictions put the global increase in mean temperature in the coming century at 1.1 – 6.4 K. If global collective agreements can be enacted we could contain these increases to less than 4 K. This is totally dependent on Greenland and Antarctic ice sheets remaining stable. If these de-stabilise we can forget all the climate models as what will happen is anyone’s guess. We would be subject to major shifts in the global climate and any meaningful predictions are not possible. The massive influx of fresh water would have a catastrophic effect on the ocean currents which move heat around the world. These currents could potentially shut down changing the climate of the entire world rapidly.

The important question now is have we reached the tipping point? Is there a point of no return from which we will reach this critical temperature where these ice sheets will collapse?  The problem is that climate is not a linear system so can change very rapidly if pushed in a certain direction. Whatever the outcome humanity is facing its most fearsome threat.

To end on a positive note, when governments have cooperated some amazing achievements have been possible. The issue of CFC gases and their damage to the ozone layer was halted; the polio and small pox viruses were all but eliminated. A new era of cooperation is now needed to come to a fair and positive outcome. 

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