What are ‘Climate Sceptics’ sceptical about?

Michael de Podesta

Michael de Podesta at work.

After giving a talk at the Royal Society of Chemistry in January 2012, I was asked to write a short article addressing points raised by ‘climate sceptics’. This article below was published in the May 2012 edition of Chemistry and Industry Magazine. 

I am a temperature measurement specialist from the UK’s National Physical Laboratory, and for the last eight years, I have been talking to the public about the temperature measurement problem of the century – Global Warming.

Through those years it has been interesting to experience first-hand how public attitudes have changed. Initially, there was a good deal of scepticism about whether there were indeed any observed changes in Global Climate. This was followed by a couple of years in which people seemed to think the issue had been settled and it was obvious that the Global Climate was changing! In recent years, amongst a wide acceptance that ‘something is happening’ people have been concerned about whether there is anything we can do. But amongst this concern – partly stimulated by the Climate-Gate furore – there has been an emergence of a group with an almost militant sceptical stance that I simply don’t understand.

So why am I am concerned?

#1: Never Mind about ‘warming’ or ‘cooling’ – why is the Earth’s surface the temperature that it is? This has been understood for more than a century, and was the subject of primary school science songs in the 1950s. The greenhouse effect makes the Earth’s surface around 33 °C warmer than it would be if the atmosphere contained no water vapour or carbon dioxide. Most of the warming (around 31 °C) comes from the water vapour and liquid water in the atmosphere. The warming arises because water – and to a lesser extent carbon dioxide – absorb the infra-red radiation emitted from the Earth. It is the emission of this radiation which cools the Earth – balancing the warming by the Sun.

#2: The amount of carbon dioxide in the atmosphere is increasing. There is no doubt about this, or about its origin: basic calculations and the isotopic signature of the changes indicate that it comes from burning carbonaceous fuels. The corresponding decrease in oxygen concentration has also been detected. The amount of carbon dioxide being put into the atmosphere is staggering. The atmosphere already contains around 2,800 billion tonnes of carbon dioxide, and each year we add roughly another 30 billion tonnes – approximately 1% of the total. The rise in atmospheric concentrations is around half this – roughly 0.5% per year – because carbon dioxide is absorbed by growing plants and by the oceans. This has resulted in a measurable decrease in the pH of seawater.

#3: What will be the effect of the extra carbon dioxide? At this point I could refer to any number of publications and models which indicate that we should expect an increase in the average surface temperature of the Earth. But actually, I don’t think that anybody knows what will happen. Although Climate prediction is easier in some ways than weather forecasting, there are many uncertainties. However in broad terms there are just three possible outcomes. Either the carbon dioxide will have no effect; or it will cause a cooling; or it will cause a warming. It would be astonishing if changing the concentration of an infra-red absorbing gas by 30% had no effect at all – truly unbelievable in fact. And although it is not predicted, a cooling of the Global Climate is conceivable – the Climate system has many non-linear elements and feedback responses. But a Global Cooling would have serious consequences too. However every published calculation I have seen predicts that the additional carbon dioxide will warm the Earth.

And that is why I am concerned.

  • Sceptics can argue whether the changes we have observed so far are real. Personally, I find the disappearance of two million square kilometres of Arctic sea ice quite convincing. But I understand that others may not.
  • Sceptics can argue whether the air temperature above the land surface of the Earth is really increasing. The 4 teams that have tried to average the meteorological records agree that since 1970 the Earth has warmed at a rate of more than 2 °C per century. But some dispute this.
  • Sceptics can argue that observed changes are just ‘natural cycles’ and point out that the ‘Little Ice Age’ was not caused by humans. To me this shows the sensitivity of the Climate System to small changes, but I understand others view things differently.
  • Sceptics can argue that it is better to enjoy the benefits of an economy based on carbon fuels and to just wait and see what happens. Personally, I think it would be prudent to switch to renewable energy sources, but I understand there are other arguments.
  • Sceptics can argue that the near unanimity of the scientific community is evidence of a conspiracy. I think there is an alternative – and simpler – explanation.
  • Sceptics can disagree with predictions of future temperature rises and sea-level changes. I sympathise: it is possible that these could be wrong.

Being sceptical about these latter points is understandable, but these are just details. We are putting colossal quantities of an infra-red active gas into the atmosphere and we don’t know what the effect will be. We should all be concerned.


2 Responses to “What are ‘Climate Sceptics’ sceptical about?”

  1. What Climate Sceptics are Sceptical About: Part 1 « Protons for Breakfast Blog Says:

    […] asking “What are Climate Sceptics sceptical about?“ a couple of Climate Sceptics contacted me to let me know. I will deal with the second […]

  2. What Climate Sceptics are Sceptical About: Part 3 « Protons for Breakfast Blog Says:

    […] my article in Chemical Industry on climate change, I have received another long missive. Whereas my first correspondent saw the […]

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