You can stop shaking your heads right now. Never mind all the reasons why the Old man shouldn’t rise to the bait, he did.

On the Netweather blog (weather geek heaven – see blogroll) , a regular said this:

Hello folks,
As everyone is aware I have questions and doubts concerning all the AGW malarky. I don’t want to have doubts or questions, I’d quite happily join the pro-camp, if I could be convinced…

 Then went on to ask if anyone was willing to give it a go. You can imagine the nature of most of the responses. Since nobody else seemed so inclined, the Old man, trusting fool that he is, weighed in with the following effort. It might not be the best aswer, but it was what i thought of as I wrote it. Is it persuasive?

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Hi xxxxx. As I know you are a sincere person, I don’t mind having a go. If any of my assumptions are uninentionally patronising, please accept an apology in advance, and if any are questionable, please question them.

I will work on the assumption that what you are having doubts about is the scientific basis of AGW. Since ‘all that AGW malarky’ could also cover issues to do with politics, energy, the environment, and a number of other things, if we agree to deal with the underlying idea – AGW – first, then other concerns or doubts can be put into context at another time.

Let’s be clear first what the discussion is about. First, there are the observations, made over time, of mean temperatures. In some areas/countries/regions, these go back to the 1600’s (the instrumental period). There are many observing stations around the world which have been collecting weather data since the middle of the 19th century, independently. Direct meaurements of the entire globe only begin in the satellite era, with reliable and regular data going back at least to the 1970s. In current times, since there are both local and global measurements being made, these are often cross-correlated, to test reliability and ensure accuracy.

In the late 1800’s, it was first observed that, on average, over a large number of discrete measurements, there was a small trend upward on mean temperatures, year-on-year. Even at this early stage, the idea was suggested that a known phenomenon of the atmosphere- carbon dioxide – might be increasing, and thereby causing the upward trend. The source of this increase was speculatively suggested to be human activity, in particular, the relatively short-term and rapid acceleration in the burning of coal and other industrial processes. this idea was largely ignored at the time, little known and little understood.

The idea of a ‘global warming’ became a matter of interest again in the 1930’s, when widespread droughts, heat waves and unusually warm weather were experienced in the USA and Europe. Because of the timing of this warm period, during the great depression, the impact on humanity was considerable, causing widespread hunger and suffering, loss of living and long-term damage to farming and other land phenomena. The original notion that the warming phase might not be entirely natural in origin was revived, and a considerable amount of theoretical work done to establish whether the physics and chemistry of the atmosphere could cause changes such as the ones which had occurred.

The question of the nature of the world’s climate and the possibility that human activities might have an influence on it was revisited in the 1970’s. One famous case relates to the paper which suggested that a thirty-year trend in slightly decreasing temperatures could be the signal that the period of warming which had previously occurred had since stopped, and a new cycle of climate might be beginning which, if it continued over many centuries, could lead to a new ice age. The idea was abandoned fairly quickly, not least because the trend stopped, and mean temperatures once again began to rise.

By the late 1980’s, following several years of much more intensive research (and the development of computers, which allowed for large data calculations to be made), the scientists who were studying climate had concluded that the global mean temperature was rising, was likely to continue to rise,and was rising at an unexpectedly rapid rate. By this time, a fairly broad range of factors which influence global climate had been identified and their relative roles calculated. After analysing the relationship between the known forcing factors (the forcings) and the changes in global temperature, it was understood that not all of the rise in mean temperature could be accounted for by natural forcings, so some other factor, forcing global warming, must be in operation.

Since the people working in this field already knew about the work done on atmospheric chemistry and physics, and the radiative forcing effect of CO2 on global surface temperature, and since the idea had already been posited that it was the increased CO2 from human industrial activity which had released many billions of tonnes of this into the atmosphere since the 1750’s, the conclusion that some, if not most, of the warming in the global record since the 1850’s was probably down to this forcing.

The AGW story since then has been much more complex. Much work has been done on the chemistry and physics of the atmosphere, and more components of it are now understood to have an effect – positive or negative – on the temperatures we experience on average. As well as CO2, Methane, Ozone, Sulphates (various), nitrates and, of course, water vapour, all contribute to the mix, and all have some effect or another. As understanding and measurement of all of these components has developed, it has become progressively easier (though still not without controversy) to allocate various effects to various components. By the early 1990’s, scientists were broadly satisfied that they had identified at least the broad picture, and the principle causes of changes in global climate, which had been experienced largely as global warming. Both the natural forcings, and the ‘human-pruduced’ forcings have been further studied and elaborated on since then, so that we are now at a stage, (summarised by the frist section of the IPCC AR4, the WG1 section) – where pretty much all of the people who specialise in studies related to the way the climate and the atmosphere works can agree that it is pretty much certain that a proportion of the global warming since the late 1800’s has been caused by human activity, and that it is very likely that most of the warming since the 1950’s has a human origin.

So, the ‘anthropogenic’ part of AGW is now understood to include a great many human activities which have as at least one of their consequences, a change in the capacity of the ‘natural system’ to absorb or ‘sink’ the excess ‘greenhouse gases’, and other effects such a changes in the location of tropical convection zones, changes in patterns of atmospheric circulation, and changes in long-term patterns of weather and climate in many regions around the world.

One way of understanding what is being referred to when ‘climate change’ is discussed is to recall those lovely pictures in the atlases we had when we were schoolkids. Next to ‘fascinating’ bar graphs showing the mean precipitation and temperature, month by month, of Rio de Janiero, London and Vladivostok, was a big world-map which showed the various ‘climate regimes’ around the world. Some I can recall are; desert, tundra, deciduous forest… remember?
Now, when a scientist talks a bout ‘climate change’, one of the things he/she could be talking about is where, and how, that map is changing. Places which were once tundra are now taiga, some arid grassland is now desert, etc. etc. So what we are dealing with is the notion that, over a period of a century or less, what was once considered to be a ‘stable regime’ of climate has been seen to be variable. Beyond this, there is the notion that the more recent changes are all in a broadly similar direction – towards a warmer world, with less rain over land and more over ocean, less extreme cold in the higher temperate zones, and rapid changes to the polar latitudes.

Some of the changes which are in the process of occurring are to do with the way in which people in some regions live in relation to the land. Widespread deforestation, overfarming and inefficient irrigation, as examples, as well as badly-conceived major public works such as the damming of rivers, all contribute to these changes. On top of these, even relatively small changes in the global average temperature can ‘knock’ a system out of kilter, and thus damage it in the long-term.

We live in a very complex society, in the sense that many of our current practices are based on certain assumptions about geophysical stability, amongst which are assumptions about the way the weather will effect agriculture during a year, what crops work where, and what sort of buildings are needed to survive extremes. Much of our infrastructure has been coinstructed on an assumption of a certain range of climate variability.

Back to the point: what AGW is pointing to is twofold; first, the identifiable causes of the measured changes in global climate, and secondly, the interrelationship between the impacts of these changes and our society.

If I wanted to understand the physics and chemistry fully, which explains how, why and how much human-produced greenhouse gase are changing global mean temperatures, I would probably have to do the postgraduate diploma in climate change at UEA, or a similar course. Since my area of specialisation is environmental ethics, I don’t have the time (and arguably, not the talent) to do this, so to a certain extent I have to engage in a act of trust. I have to decide whether or not I can trust the people who work in the fields related to climate, such as atmospheric chemistry, to know their jobs, report their work honestly, and understand the implications of the research they do and the discoveries they make. Whilst not all of them do this, on balance, most them do, and therefore I choose to trust them. Since their work is overseen by others with experience and knowledge, and criticised and studied by fellow scientists all around the world, and since their reputations (and livelihoods) depend on them not making bad mistakes, I am reassured in my inclination to trust their words and work, but also concerned that the entire system is imbued with an innate conservatism, so that the more radical notions of consequences migh not come out so clearly.

My suggestion, in a nutshell, then, is that, if you are not in a position to spend a year or more studying the basic equations and formulae directly, instead you should decide whether, on the balance of things, you are willing to trust other people – dedicated, hard-working, honest and assiduous people – who are expert in their fields, to tell you what is or is not happening. Please note, though, that there is a difference between not trusting and not wanting to trust; if your case is the latter, it may be that you could consider whether your wish to not have to trust these people is founded on the underlying wish that AGW isn’t really happening.

It is a simple truism that none of us can know everything, and few of us have the talent or skill to study and analyse in depth the work of scientific specialists. This does not stop us from trusting that an engineer has designed a bridge well enough to allow us to cross it in safety, or a that a doctor has correctly diagnosed and treated an illness. Living in a technological society, in fact, we place an implicit trust in literally thousands of different kinds of specialists and experts, every day; we even trust them with the safety of our own children. Some of the people who inhabit NW are experts in their own fields.

So, I am afraid, in a sense my simple response to your question ‘why should I believe all this AGW malarky’ is ‘because the experts tell us so’. They might be wrong. They could have missed something, or left something out. Some of them might be jumping on a bandwagon. But the sheer weight, the mass of material which supports their assertion that AGW is real, especially when measured against the material which attempts to contradict it, should also, in itself, be convincing testament to the rigorousness of the original hypothesis.

This is a rather longer reply than I had planned. I know there are weaknesses and errors in it, and that some matters are not addressed, but I hope that the underlying reasoning is itself persuasive.

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