What does two degree Celsius “average global temperature” really mean?

 The world’s leaders want to limit the rise in average temperatures to two degrees Celsius by 2050. This sounds like a very clear statement of ambition. Everyone understands that limiting averaging temperature rises to two degrees would be a good thing, because that it what the scientists advise, isn’t it? The truth is that the ambition is not clear and really I am not sure what it limiting average temperature rises to two degrees Celsius actually means. As usual the politicians have fudged things and I shall explain why I do not understand what they mean.

There are some difficulties in understanding what “limiting the rise in average global temperatures to two degrees Celsius by 2050” means. The statement raises more questions than it answers.

If we are to be pedants then I think that there is no such thing as an average global temperature. A temperature is a measure of heat at a given point of time. A body, such as the globe, only has a specific temperature if it is in state of equilibrium, which the globe never is. A state of equilibrium means that a body neither emits nor accepts energy and heat is simply a form of energy. There is never a time when any part of the earth neither emits nor accepts energy.

Therefore there is no average global temperature.

OK, you may say, this is simply pedantry. Well, instead of looking at the subject thermodynamically, let us look at the statistics of things. Does the phrase “average global temperature” have any meaning?

You can get many different average global temperatures. You can measure the highest and the lowest temperature every twenty four hours in every part of the world at sea level and take an average; you can measure the same places’ temperatures at six hourly intervals and get a different average. You can measure surface air temperature, air temperature above the surface by any number of measurements, land temperature and get all sorts of different averages.

Then there are many different places on the earth that customarily have different temperatures at different times. James Hansen points this out.

Weather stations provide temperature data. Mostly they provide for public consumption (and the phrase “average global temperature” is for public consumption so it is fair to use this as a comparison) the average high and low temperatures. Here are the average monthly highs and lows for London, which has a long history of weather data.

        London      min     max    





























































Do world leaders mean that they will limit the average monthly highs and lows of every place in the world by two degrees?

 It would be wrong to blame the politicians for this lack of clarity. They are simply adopting the language of the climate change scientists. The climate change scientists tell us that we must limit the change in temperature to two degrees Celsius, but that advice is very difficult to fathom.

If you add two degrees to London’s monthly average temperature rises you will see that, the temperature of February becomes March, and September becomes August while June becomes July and July becomes something new.

That is probably the best way to interpret the politician’s ambition, but surely it is not for me to try and interpret their language but for them to speak so that I do not need to guess what they mean.

6 Responses

  1. The conservative estimates of the UN Panel on Climate Change, out-of-date even before they were published, have told us that reaching an atmospheric level of 400 ppm CO₂ would give us a 50-90% chance of exceeding 2° Celsius warming, which would risk triggering a nightmare scenario. This is not good. Would you get on a plane if you were told you only had a 50-90% chance of reaching your destination alive?

    And just what is this number 2°C all about anyway? Is it really safe to allow global temperature to rise this high? Or is this instead just a number picked by global leaders because it’s the “politically feasible” one? Call me a cynic, but are we being tricked into a false sense of security by being told we’ll all be safe if global temperature doesn’t go up more than 2°C?

    If your child’s body temperature were to rise to 40.6°C or 102.2°F and stay there, he might be able to survive for a while, but eventually he would get very ill and probably die.

    • Dorothy
      I was looking for a good analogy to make people understand two degrees; You conceptof a child’s temperature is very powerful.
      The problem is that no one knows for sure whether the projectiosn are rreasonable, alarmist or conservative. However, as you rightly say – why should we take any chance on them?

      Best regards


    • Dorothy
      I was looking for a good analogy to make people understand two degrees; You conceptof a child’s temperature is very powerful.
      The problem is that no one knows for sure whether the projectiosn are rreasonable, alarmist or conservative. However, as you rightly say – why should we take any chance on them?

      Best regards


  2. A 2 degree rise in temprature spells the biggest hike in world pollution and warming we have ever seen, everyone will turn on or up their air conditioning to stay cool.
    Millions of people will have to move because they will not be able to grow the very thing that keeps us alive, FOOD, this has alreadu reared its uglynhead in Africa.

    Governments around the world today are using using the global warming issue to make money in so called green takes, we are in efect paying to pollute,

    The green issue also takes our minds off the real issue and that’s the depletion of oil and what is happening throughout the world today in getting enough of it to supply the biggest users, the USA and China.
    We are now in constant resolution for the black stuff, than we have ever been throughout history, and in effect wasting a huge amount of it in doing so.

    As the world population grows so will the temprature, its going to be one hell of a war for oil, our sons, brothers and mothers and father are all suffering in order of securing the beach head for oil, we wasted 12 years of it in the first Iraq war when 12 years worth of oil went up in smoke.

    It is known that the worlds 4 biggest oil fields are already in decline, so best learn what we need to survive, skills and ways of getting enough food to last through the food winter, or we are going to fall by the wayside.
    Remenber this statement, civilisation is only three meals away.

  3. i think people dont see the huge impact that changing little tings do in the enviorment, i dont think this is a way for the goverment to make money although that always happens but, if we dont care about where we live we will not have anywhere to live , the earth is living planet until now but if we destroy it like parasites it will aniquilate us surely on the long run no joke

  4. and also insted of thinking of oil and the wars start thinking about whats next, becaus saying that civilization is only three meals away comon its like a person thinking he cant think, like i need to survive now i dont care what happens and thats the mayor problem that millions of people think that way every day and one day your going to wake up and say i should have don this and that becaus you didnt see the big picture, its up to our governers to guide us through this becaus its amazing there are laws so strict for certain things and this has just passed by like it means nothing , nobody cares because there are some bigshots with lots of money from the oil and other industries that seem to be more powerful than the so called leaders of the world , its terrible how they can sleep at night just knowing what they do
    and what will happen to their descendents because all they money they inherit them wont do any good if they dont have a place to live in

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