The central issue in the debate over climate change is the question: is climate change caused by humans burning fossil fuel and releasing carbon dioxide into the atmosphere?
Although this question has been debated for many decades, it rose to international prominence following a seminal piece of research by scientists at Grenoble University on Antarctic ice cores, published in 1999.
Historical climate change
The snow that falls each year in the Antarctic forms frozen layers that can be used for historical analysis, like tree rings. The snow becomes compacted into ice layers containing a number of proxies that can be measured, such as trapped air bubbles, dust and ash.
This enables climatologists reliably to reconstruct the temperature of the earth’s atmosphere in the past and to measure the amount of greenhouse gases, such as Carbon Dioxide in the past. Reconstruction is done mainly by isotope analysis.
The deepest series of cores so far extracted is from the Russian “Vostok” Antartctic base (Vostok means East and was the name of an early Russian Antarctic exploration vessel.) The base is about 1,300 Km from the South Pole and has an elevation of 3,488 metres. It is the world’s “pole of cold” – the coldest, driest place on earth. The warmest it ever gets is -12 degrees C.
The Russians cored to a depth of 3,770 metres. This represents about 420,000 years back in time. An international team at Grenoble university, led by Jean-Robert Petit, has been working on the Vostok cores for many years. In 1999, the Grenoble team published an article in Nature magazine that has formed the basis of much climatology discussion and debate for the past 15 years.
The Nature article contained a graph which has been widely reproduced. You can view the graph on Wikipedia here : http://en.wikipedia.org/wiki/File:Vostok_Petit_data.svg It is reproduced at the bottom of this blog as Figure 1.
The graph formed a key piece of evidence in Al Gore’s film in “An Inconvenient Truth” as evidence that the increase in carbon dioxide, and other greenhouse gases produced by humans over the past two hundred years, is a major cause of global warming.
It’s easy to see why Al Gore and many others have reached the conclusion that CO2 is connected with the rise in atmospheric temperature because of the remarkable correlation between the top three curves of the graph – air temperature and CO2 and dust concentration.
However, what is not obvious from the graph as it is normally presented is its scale. When the scale is enlarged so that one can pick out individual years, or decades, it at once becomes apparent that the rise and fall in CO2 does not come before the rise and fall in air temperature, but after. In fact about 800 to 1,000 years after.
This finding, that the change in CO2 levels follows about 1,000 years after changes in atmospheric temperature has been confirmed by at least three other studies (see references).
When challenged on this point, those who believe climate change is man made reply by saying that the graph shows that every so often the atmospheric temperature begins to rise as a result of some at-present unknown mechanism. After the unknown mechanism has been heating the air for about 1,000 years, the increased level of CO2 then “kicks in”, takes over and becomes responsible for further heating , through the greenhouse effect. What this initial mechanism is, remains unknown, but its supporters remain hopeful that further research will uncover it.
Critics of the “unknown mechanism” idea point out that, even after a thousand years, the variation in CO2 still comes after the variation in atmospheric temperature – and that, in physics, causes always precede their effects, rather than following them.
Is today’s climate change “unprecedented”?
Proponents of a human cause for climate change sometimes describe the current maximum as being unprecedented. But even a quick glance at the graph showing the history of climate is enough to demonstrate that there have been four previous occasions in the past 420,000 years when there were maxima of atmospheric temperature and CO2 comparable to today’s. We know for certain that the previous four maxima could not have been cause by humans burning fossil fuel, because there were very few humans, there was no industrialisation and burning of fossil fuels was negligible.
If we know that for certain that the previous four maxima were not caused by humans, then what scientific reason is there for supposing that the current maximum is so caused?
Is there an alternative explanation available that doesn’t involve unknown mechanisms? There is an alternative and it was included in the Grenoble team’s original Nature article but was omitted by Al Gore and others. The complete graph is pictured on Wikipedia here:- http://en.wikipedia.org/wiki/File:Vostok_420ky_4curves_insolation.jpg
It is shown below as Figure 2. You’ll notice that the original graph also included another curve at the bottom labelled ‘Insolation’. Insolation means the amount of heat arriving at the earth’s surface from the sun, which varies over time. This too, correlates well with the rise and fall of atmospheric temperature.
Climate scientists reject insolation as the cause of climate change, despite the correlation found by Petit et al, because they say that the increases in insolation are inadequate to account for the amount of global warming. Some of the world’s climate scientists – notably Henrik Svensmark professor of Solar System Physics at the Danish National Space Institute – think that insolation and cosmic radiation are indeed the cause, but their research findings are marginalised.
The role of carbon in the greenhouse effect.
The greenhouse effect – the trapping of the sun’s heat in the earth’s atmosphere – is due to a number of gases in the atmosphere. Supporters of the idea that climate change is human generated say that the gases that contribute most to the greenhouse effect, in order of importance, are:-
- Carbon Dioxide
- Nitrous Oxide
- Miscellaneous gases such as CFCs
Of these, they say that Carbon Dioxide is not only the most important greenhouse gas but also that humans are contributing significant amounts to the atmospheric burden by burning fossil fuels and that this is the primary cause of climate change.
Although this list is correct it – inexplicably – leaves out the most important greenhouse gas: water vapour and water droplets in the form of clouds. Estimates of the contribution of water vapour as a greenhouse gas vary. It may be as much as 95% of the greenhouse effect. NASA estimates it as “more than 70%”.
This means that the most publicised greenhouse gases – Carbon Dioxide plus Methane plus Nitrous Oxide plus CFC etc.- account for as little as 5% of the greenhouse effect even when added together.
Moreover, of the greenhouse gases, aside from water vapour, Carbon Dioxide accounts for about two-thirds – that is as little as 3%. Of this, about 0.01% of this is man-made. So that even if the world reduced its carbon emissions by 10%, the total effect would be negligible.
Those who support the view that climate change is human-made say that – unlike CO2 – the levels of water vapour present in the atmosphere are transient and continually changing. However it remains true to say that the average amount of water vapour in the atmosphere is fairly constant over time – especially the time scales of the Vostok core data.
Is the Earth getting warmer?
The temperature of the earth’s atmosphere has varied widely over hundreds of thousands of years. Those who believe humans are causing global warming have recent human history in mind. Over the two centuries since the beginning of the industrial revolution, atmospheric pollution has increased and so has atmospheric temperature. It is a perfectly legitimate scientific project to investigate whether the two are linked. So what do the most recent (direct) measurements show?
There are four world laboratories that track Earth’s temperature (the Hadley Climate Research Unit at East Anglia University in Britain, the NASA Goddard Institute for Space Studies in New York, the Christy group at the University of Alabama, and Remote Sensing Systems Inc in California). They are in unanimous agreement that the earth has been cooling, not warming since 1998.
Until a few years ago, the climate change lobby used the phrase ‘global warming’ as a convenient shorthand way of expressing the view that human-generated carbon emissions have been causing the atmosphere to heat up. However, since the atmosphere started cooling 15 years ago, they have dropped the phrase ‘global warming’ and now speak instead merely about ‘climate change’. The change in language does not represent a change in the science – merely in the presentation of a theory.
In recent years, the amount of carbon entering the atmosphere has continued to grow. From 1980 to 1998, for example, CO2 rose from 340 parts per million to 370 parts per million. If CO2 was the cause of heating, why has the heating stopped and gone into reverse while CO2 emissions have continued to grow? The climate change lobby’s answer is that nature is complicated and we don’t yet know all the answers.
The climate change lobby has adopted the name “hiatus” for this cessation in warming, although there no scientific basis for using a term that suggests only a pause. Most recently of all the US National Oceanic and Atmospheric Administration (NOAA) has published an article in the journal Science, saying they have re-analysed the data and find that the earth is still warming after all. NOAA is not one of the four scientific institutions tasked with measuring temperature, but an organisation tasked with disseminating official information. Their conclusions are scientifically inexplicable and have already been challenged by scientists.
NOAA contrived to make the hiatus disappear by doubling the warming trend in the 1990′s, adjusting the pre-hiatus temperatures downwards and inflating recent temperatures. Georgia Tech climate scientist Judith Curry says that NOAA excluded extremely accurate sea buoy data in order to erase the hiatus in warming. Curry wrote, “This short paper in Science is not adequate to explain and explore the very large changes that have been made to the NOAA data set. So while I’m sure this latest analysis from NOAA will be regarded as politically useful for the Obama administration, I don’t regard it as a particularly useful contribution to our scientific understanding of what is going on.”
Are we experiencing unprecedented climate change?
It is undeniably true that we are undergoing a period of rapid and sometimes violent climate change. But is this unprecedented?
The ‘Vostok’ ice cores show that the present relatively warmer spell is just the latest in many such interglacial periods, some of which lasted 100,000 years, before the ice age returned.
12,000 years ago, the current warm interglacial period began and sea levels around the world rose dramatically as the ice melted. Human settlements in what is now the North Sea were inundated in less than a human lifetime. None of these earlier climatic variations can be attributed to human-generated CO2. So what scientific reason is there to think that the current variation are caused by human activity?
Many well-informed people, including climate scientists, are well aware of these facts but are still legitimately concerned that human activity could be having adverse long term effects whose nature is at present unknown. They express these concerns by saying, for example, “It’s better to err on the side of caution”, or “we owe it to our grandchildren not to mess up the planet and leave them to clear up”, or “better to spend millions now than billions later”. I share their concern and sympathise to some extent with these sentiments.
What I do not accept is that their concerns are based on substantial scientific evidence – that they represent the rational scientific viewpoint. In reality they are as superstitious as fears about the “millennium bug” crashing all the world’s computers.
Is there an explanation available of why many well-informed and no doubt sincere professional scientists can ignore the empirical evidence and prefer instead to adopt a stance as advocates of a group belief? There is a detailed history of this behaviour and analysis of the reasons for it in my book “Alternative Science” , obtainable from Amazon.com here.
1,5. Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica, J. R. Petit et al, Nature 399, 429-436 (3 June 1999)
2. Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations. Hubertus Fischer, Martin Wahlen, Jesse Smith, Derek Mastroianni, Bruce Deck , Science 12 March 1999: Vol. 283. no. 5408, pp. 1712 – 1714
3. Mudelsee, M. 2001. The phase relations among atmospheric CO2 content, temperature and global ice volume over the past 420 ka. Quaternary Science Reviews 20: 583-589.
4. Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming, Lowell Stott, Axel Timmermann, Robert Thunell. Science 19 October 2007: Vol. 318. no. 5849, pp. 435 – 438