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Sunday, July 15, 2007

Global Warming - anthropogenic or not

Not many people would argue today that we are not in a period of global warming. Glaciers all over the world are disappearing, Spring, as measured by bud burst or the return of migratory birds is getting steadily earlier and earlier, Arctic ice is thinning and so forth.

It is less obvious, though, whether it is caused by the measurable increase in greenhouse gases or by natural (non man-made) phenomenon. There is even a niggling doubt whether or not the increase in atmospheric carbon dioxide is man-caused. I personally have no idea what the truth of the matter is. I don't have access to original data and even if I did, I doubt if I could make a creditable analysis of all but the simplest information. Until recently I just assumed that the anthropogenic model was correct because of the overwhelming publicity for this theory. However I started to come across the arguments of a number of sceptics. It is interesting, to present their arguments against the man-induced-warming hypothesis for examination. Science mustn't be turned into religion - into a belief system from which all consequences derive. Science is strong when we listen to skeptics and examine their arguments based on the evidence available and not based on our pet beliefs. So, what are the arguments against global warming being caused by man.

Measurement Errors

First a comment about our method of measuring the degree of global warming. While the retreat of the glaciers, and other physical evidence, is clearly visible and suggests very strongly that global warming is occurring, temperature records, surprisingly, are suspect. Why is this. After all, a mercury thermometer, calibrated against the freezing and boiling point of water, set in an approved weather box and recorded manually over the past few centuries should be a pretty reliable measure of global warming. Unfortunately not. Take a weather station set up 300 years ago in Rural England 50 miles outside of London. When the station was started, the area was covered with trees; fields were relatively small and there was no town of any size anywhere in the vicinity. Since then, London has expanded and the same weather station is now surrounded by high rise apartments. It is well known that urban areas are warmer than adjacent rural areas due, both to the energy they use and release as heat and the effect they have of trapping sun energy. So what does a scientist do (assuming he actually does something). He can stop taking measurements at this site or he can make a correction. The correction will be based on the best information available on the relative effect on temperature when a site is urbanized. A corrected value is already not a primary source measurement and as such its accuracy is suspect. In addition, buildings are continually being pulled down to make way for new buildings so the degree of heat augmentation due to urbanization may be continually changing.

Another confounding effect results from the advance of measuring technology. Suppose we introduce a recording, electronic thermometer. It must be calibrated against the original mercury thermometer and eventually it is relied on. With the increase in the wages of people who read the weather stations, it is very tempting to automate such systems. With continual recording there is now the possibility of averaging (integrating) the temperature over the whole 24 hour period rather than just recording the maximum and minimum and averaging these. All these changes introduce enough possible errors to make a physicist tear his hair out.

Another type of measurement which has come into vogue is radiation readings of the earth from satellites. Again, calibration against the original thermometer and against the electronic instrument is undertaken.  At each change we reset the base line and to some extent make previous data obsolete.

As soon as a new instrument or measuring technique is used, there is an added source of error. A dose of healthy scepticism and examination of the details of the way temperature measurements have been and are being taken is wise before placing too much faith in direct temperature readings. Having said that, the indirect indications that the climate is warming are pretty convincing, so what are the arguments against it being caused by man and his green house gases.

Climate Change Has Always occurred
One arguments against the anthropogenic model comes from the recent changes in climate. In the middle ages from around 1100 to 1400 the earth was quite a bit warmer than it is at present. Incidentally it was a period of great prosperity and many of the famous cathedral's of Europe were built around this time. Hence its name of a "climate optimum". Places all over England have names such as vineyard road winery cottage and so forth commemorating this period and suggesting that the climate was suitable for grapes. A bit later starting around 1400 and continuing to around 1850 we had the little ice age. The oft-quoted indication of this ice age was the freezing over of the Thames River as recorded in literature and art. Going back further we have the bronze age hipsithermal , also a climate optimum" between 8000 and 4000BP. Further back, the end of the most recent of a series of glacials* occurred 10 to11000 years ago. All this quite dramatic change, both warmer and cooler, happened without any help from humans. In itself, this is not an argument against the anthropogenic theory but serves to set the scene. Global warming (and for that matter, global cooling) has occurred in the very recent past with much larger temperature fluctuations than we have observed so far in our present temperature rise. Incidentally, the oft quoted disappearance of the Kilimanjaro glacier started in the 1880's, arguably before significant carbon dioxide was added to the atmosphere.

* interglacials.  The previous interglacial was the Eemian, around 125,000 years ago and the present interglacial is called the Holocene.  

Carbon Dioxide Causes Global Warming
What about the increase in atmospheric Carbon Dioxide. If you watched the film, An Inconvenient Truth by Al Gore, you would have seen a graph with Carbon Dioxide and global average temperature marching along hand in hand. If you look closely, though, it looked as if changes in temperature occurred before changes in Carbon Dioxide. If you want to suggest cause and effect between these two parameters rather than just correlation, you would be very tempted to suggest that a change in temperature caused a change in Carbon Dioxide rather than the contrary. Scientists who have noticed this 'anomaly' have suggested a mechanism. It is known that Carbon Dioxide is much more soluble in cold water than warm water. You see this with your favorite fizzy drink. Open a warm coke and you will find yourself wearing it rather than drinking it. Since Carbon dioxide dissolves to a greater extent in cold water than in warm water, as the oceans warm up they may give off Carbon dioxide or at the very least, absorb carbon dioxide less readily. The oceans are so large and the circulation is in the order of a millenia or two so the suggestion is that the lag is due to the carbon dioxide absorbing inertia of the oceans, causes Carbon dioxide levels to lag temperature changes. Looking at derived temperature data from such markers as the delta Oxygen 18 ratio in foramanifera shells, oxygen and hydrogen isotope ratios in ice and at the carbon dioxide concentration in bubbles in ice cores, it appears that carbon dioxide has lagged about 800 years behind temperature changes over many many millenia.

(The above article also deals with reduced stress on trees with higher carbon dioxide concentrations)

A rather interesting bit of information which I haven't seen yet is whether the surface of the ocean is actually warming now. This might give us a clue as to which is the cause and which is the effect.

Another anomaly occurs when you look at the recent temperature/carbon dioxide record in more detail. A marked increase in carbon dioxide production has occurred from the end of the Second World War up to the present. However, from about 1940 and continuing for some 4 decades, temperature actually decreased. In fact, around the 70's the theory in vogue was that we are in for another ice age. Following this period, the temperature increased again, oddly enough starting just as we had the industrial slow down caused by the oil crisis of 1973. Moreover,if you look at the recent temperature rise (the blade of the hockey stick) much of this warming happened prior to 1940. Some wee wrinkles need to be explained before we accept the anthropogenic theory whole hog.

Sun Spot Activity
There is, allegedly, a factor which correlates more closely with temperature than Carbon dioxide concentration. This is sun spot activity and sun spots have been observed and recorded for centuries. The sun spot activity at present follows about an 11 year cycle but there have been long periods when sun spot activity has been very low. One such period coincided with the little ice age. Again some scientist have suggested the mechanism that might explain the connection.

When fast moving radioactive particles wizz through saturated air, they leave a "con trail" much as is produced by a high flying airplane. This creates nuclei around which clouds can form. An early device used to view radioactive particles known as a cloud chamber shows this effect in the laboratory. A hermetically sealed, well lit box is lined with black material. Some open water and a wick keeps the air in the box saturated. A piston on one side of the box is pulled out, lowering the pressure a little in the box (or dry ice is used to produce supersaturation by cooling). However, in the absence of nuclei, no cloud droplets appear. If you now have a source of radioactive rays such as even a simple piece of granite, you will observe 'con trails' appearing. You can go one stage further by imposing a magnetic field across the box. Neutral particles continue to fly straight, positively charged particles curve one way and negative particles the other way. You can get an indication of what sort of particle is making the trail by the way they fly. Remember this deflection effect. It becomes relevant a little further on.

The same, so the theory goes, happens in the atmosphere. Cosmic rays from distant super novae, consisting of the charged nuclei of atoms, some of them quite large (iron for instance) and traveling at relativistic speed crash into our atmosphere. They are so energetic that they cause cascades of secondary particles and even tertiary particles. If they pass through saturated atmosphere, they make cloud trails which are nuclei for further condensation. That is to say they make clouds. Clouds, being white, reflect the sun's energy back into space, without it having the chance to warm up the earth.

Note here that except for some of the UV radiation which is absorbed by oxygen molecules high in the atmosphere, most of the sun's radiation passes through the air without heating it up. ie. The atmosphere is transparent to most of the radiation coming from the sun. Heating occurs when the radiation is absorbed by the earth which in turn warms the adjacent air. This heating from below combined with the latent heat of water is the source of most of our weather. With more high cloud, less radiation is available to warm the ground and hence the adjacent air.

So what do sunspots have to do with all of this. Apparently periods of sun spot activity are also periods of strong solar magnetic fields and the magnetosphere extends far beyond the orbit of earth. Remember our cloud chamber. In a magnetic field, charged particles are diverted from their paths. In periods of high sun spot activity, so the theory goes, the cosmic rays are diverted by the stronger magnetic field of the sun and don't hit the earth and less cloud is produced. The world warms up as more sunlight hits the surface of the earth. High sun spot activity results in warm periods, low sun spot activity in cold periods. The sun's magnetic field has doubled over the 20th century which would lead one to expect higher temperatures if the above mechanism is indeed responsible for global warming.

Glaciers Melting
There is not much doubt that glaciers are melting world wide - or at least they are retreating which could be due to less snow fall in the upper snow collection areas. Let's not quibble. Besides, whether or not there is less snow falling is pretty easily determined if there are reasonable historical snowfall records so one can quickly work out what is causing the retreat. In the Himalayas, and possibly elsewhere there is another factor which must be taken into consideration besides the increase in Carbon Dioxide. This is the brown cloud which is now permanent over Asia. It is the result of the burning of a wide variety of fuels for industrial and domestic purposes and from extensive forest burning, along, often with the peat deposits under these forests. This brown haze absorbs sun energy before it reaches the ground and is estimated to have warmed up the air at the altitudes of the Himalayan glaciers by a quarter of a degree per decade since 1950. This amounts to about a degree and a half which is quite serious vis a vis the stability of glaciers. This is actually an argument on the side of the anthropogenic model since, while it is not caused by carbon dioxide, it is certainly anthropogenic. It is, however,an argument for the redistribution of the heat from the sun rather than an overall warming. The good news is that if the generation of this material was stopped tomorrow, within a couple of weeks it would be largely cleared from the atmosphere. This is in contrast with Carbon dioxide which takes much longer to be removed from the atmosphere.

As mentioned, the Kilimanjaro glacier has been retreating from well before the major increase in Carbon dioxide. Since there is no indication that over this period the amount of soot in the air in this region increased, this would support the argument that there is global warming but it is non anthropogenic.

Vested Interest
When observing peoples actions (such as promoting one side or the other of the anthropogenic climate change argument) it is often useful to look at their motives. People who deny that the presently observed climate change is anthropogenic are often accused of being in the pocket of the big oil companies. I'm sure that many of them wish they were. Maybe the odd one is. However, one mustn't ignore, vested interests on the opposite side of the argument. Since Maggie Thatcher's campaign to promote nuclear power in order to gain independence from overseas oil and domestic, strike-plagued coal, great amounts of money have been put into research on climate change with the underlying 'flavour' that this money is given so that the scientists can prove their theory of anthropogenic climate warming. Someone who's theses is that climate change is completely natural will get short shrift from the granting agencies. In the USA, prior to the 70's, annual research grants for climate studies ran at about $170million. Today the figure is closer to $2 billion. An awful lot of scientists will be out of a work and/or find grants very hard to come by if the anthropogenic model is dis-proven. None of this proves one way or another whether the anthropogenic model is correct. I even hesitated whether to use the argument here but in the words of the elementary school playground "they started it". It does make one realize, though, that there are vested interests on both sides. mustn't ignore the vested interest of politicians. After some reluctance, a lot of politicians around the world have enthusiastically endorsed the 'reality' of anthropogenic climate change. They have introduced legislation which deals with ameliorating the emission of Carbon dioxide. Much of the type of legislation they have initiated is designed to make the banks rich, in which they likely have shares.   They have also invested significant political and emotional capital on the anthropogenic side of the argument. They will not be amused (to paraphrase Queen Victoria) to be told that climate change is not actually anthropogenic after all.

Another vested interest and very ugly interest at that, is the desire of the already industrialized nations to remain on top. In many cases this is at a gut-instinctual level although in some cases it has been openly articulated. We have evolved as a tribal animal and our strength derives, to a large extent, from how strong our tribe is. At a very more cynical level, it is much easier to exploit the natural resources of a simple, un-united people that it is to exploit a united educated people. Witness all the exploitation that Gandhi fought against during his life and this was against what we think of as one of the enlightened countries of the world. Indians weren't allowed to make their own salt from sea water or weave their own cloth from their own cotton because the enlightened colonial power in charge, was making money out of selling them these products. Talk about economic abuse!!! The anthropogenic global warming theory is brought forward to argue that the undeveloped parts of the world should not use their oil and coal resources but should depend on wind and solar. All the while the developed nations continue to burn these resources, derived, not only from their own countries but often from the very countries that they say should not use them. The vested interest argument doesn't weigh on either side of the scientific debate but it does let one realise where some people are coming from.

The atmosphere isn't warming as it should.
An argument against global warming being caused by Carbon dioxide involves the models which predict where warming should occur. As mentioned above when light from the sun hits the earth, some wave lengths of the UV are absorbed in the upper atmosphere ionizing oxygen molecules and heating this layer. However by far the greatest part of the electromagnetic energy (light and similar wave lengths), travels through the atmosphere without being absorbed. The atmosphere is transparent to most of this radiation. These wave lengths warm the ground and the ground warms the adjacent air and both radiate long wave radiation in the infra red spectrum. These long wave lengths are absorbed by green house gases (this is why they are called green house gases) and warm the atmosphere. The models say that we should see most warming in the mid levels of the atmosphere known as the troposphere around 10 km altitude. This is apparently not happening. Instead, the the atmosphere is warming mainly near the ground as would be caused by a reduction in cloud cover which in turn fits the sun spot model. Could this be another small glitch that has to be explained in the anthropogenic model.

Weather Disaster Scenarios in Error

Much is made of the theory that with global warming we will have much more severe weather. This is used as an argument for doing something about our green house gas emissions. There is some truth in this assertion in that weather is caused to a large extent by water vapour condensing, releasing latent heat and forming storms. Hurricanes, for instance, need surface water temperatures around 26 degrees and warmer, to power them. However, on the other side of the argument, meteorology texts state that much of the severity of our weather depends on the difference in temperature between the equator and the poles. It is well documented that, as the world is warming up, the greatest warming effects are at the poles. The temperature difference between pole and equator is decreasing. It will be interesting to see, as the world warms up, if it continues to do so, where we have more severe weather and where less. Of course this has nothing to do with whether global warming is anthropogenic or not but does raise some questions about the use of the threat of weather disasters to promote measures to counteract carbon emissions. There is a tendency now to blame any severe weather event on global warming. Katrina was a case in point. However Katrina was arguably not an unusual weather event but rather a normal weather event that hit an unusual target.

Disaster Predicted
A raft of disasters besides wild weather are predicted if our climate warms.They are used to reinforce the arguments against using oil or coal. It is stated, for instance that the Polar Bear will disappear. This is odd since the polar bear not only survived our own bronze age hipsithermal event but many inter glacial periods which have occurred in the most recent glacial age. It would seem much more likely that if the Polar Bears are disappearing, the cause is some other man made effect. For instance, volatile materials such as DDT PCB"s and mercury tend evaporate from the tropics and condense at the poles. It is known, for instance, that human milk from Eskimos has more of these harmful substances than human milk from warmer climates despite their distance from point sources of pollution. Could this, or some other man made change be a cause of the demise of the Polar bear (if indeed the polar bear is disappearing).

It has also being stated that with global warming, tropical diseases will spread north. This may or may not be so but some of the diseases we think of as tropical are not and various sanitation and other measures are more likely to have be the reason we no longer see them in northern climates. Cholera has been rife in Europe in many ages and one of the worse outbreaks of Malaria occurred in Russia in 1920 all the way up to the arctic circle. Remember that this was at the tail end of the little ice age. Each scare story of this sort should be examined on its merits and it is not a bad idea to talk to experts who study the field in question all their lives before postulating such effects from global warming.

Drama in Science
If you don't think that we are drama junkies, just look what we watch on Television. There is very little publicity value to a scientist reporting that yes, temperature will rise a little and then fall a little and everything will be much the same over all. There is not much more publicity value in stating that yes, the world is warming but it is natural and there is not much we can do about it. It is much more exciting and reportable to say that we are going into another ice age or alternately that global warming will inundate New York and London. Indeed in the early 70's, the prevailing theory, based on 4 decades of falling temperatures, was that we are heading into an ice age. Scientists are human and there is a strong motivation to be able to report something dramatic. Also a dramatic story is also much more likely to get a research grant.

We mustn't forget our reporters. Climate change in particular and ecology in general has become such big news that some papers have special ecology reporters. What reporter is going to report that climate change is not man made when everyone else is saying it is. His very job is dependent on the drama he can put into his disaster stories. As usual it is valuable to know what motivation a person has when evaluating what he says. Vested interests raise their ugly heads yet again.

Actions against Global Warming Good for the Earth
In the back of many peoples minds is the concept that even if global warming is not anthropogenic or even if it is not even happening, the measures we will take to reduce our production of carbon dioxide plus the methods we put in place to sequester carbon dioxide will bear fruit in other ways. Reducing the use of coal and oil, for instance, leaves more of this "much to valuable to burn" resource in the ground for future generations. Such materials would be much better used for industrial feed stock and not burnt as fuel. Less combustion of fuel reduces air pollution. Planting of trees has many beneficial effects such as the mitigation of flash floods, increase of rainfall, reduction of soil erosion etc. Development of local diffuse power generation, from roof top solar panels has an " Internet effect" reducing the vulnerability of our power supply to various disasters, natural and man made, and reduces our dependence on offshore power sources. All this is very positive. These arguments are compelling but there are always dangers in doing the right thing for the wrong reasons. Better we understand what is actually happening and take these same measures for the right reasons. Namely to stop wasting a valuable resource by burning it. More important, if we think that global warming is inevitable we will expend our energies/money in different directions than if we think we can stop global warming. Instead of concentrating on sequestering Carbon dioxide, for instance, we might start research on how Iowa farmers can start growing rice or how Eskimos can start to grow wheat (only slightly with tongue in cheek)

So much for the arguments. This is where the fun starts in the scientific process. We have the currently accepted theory that Climate warming is a reality and it is anthropogenic. On the other hand we have the contrary, less accepted theory that Climate warming is happening but no, it is not (or mostly not) anthropogenic. Instead, the observed changes are a natural, not a man-induced phenomenon. If the less popular theory is correct, certain things should be observable.

1. If global temperature is dependent on sun spot activity, one of the pillars of the non-anthropogenic model, one would expect that the medieval warming was a period of high sun spot activity. Likewise the bronze age hipsithermal should have been a period of high sun spot activity. Conversely, the little ice age should have been a period of low sun spot activity. Apparently this is so for the little ice age but we don't have any direct observational data from the warm periods. Direct observation, however, is not absolutely necessary since sun spot activity can be deduced by certain proximal data such as isotope evidence (Barium) in ice cores. One must, always be aware of confounding factors. For instance, the little ice age which cooled areas adjacent to the North Atlantic may not have been part of a general global cooling but only a localized effect, say, due to the Gulf Stream shutting down. It would be well to first check the isotope record for foramanifera deposits which show the sea surface temperature in other parts of the world before concluding that any of these warm or cold periods were global. As far as sun spot activity goes, we are nearing the end of a sun spot cycle and some scientists have predicted that we may now enter a period of low sun spot activity. If so we would expect cooler temperatures despite increased carbon dioxide emissions. Only time will tell.

2. If global warming is dependent on sun spot activity, one might see an 11 year temperature wave in the recent recordings for individual weather stations. In such a short period, background noise might be too great to separate the signal from the noise but it is worth a look. In fact, since I wrote this article, it has been reported in New Scientist that some scientists have found an 11 year cycle in temperature of 0.2 degrees. They, oddly enough, suggested that this is an argument for, not against, anthropogenic warming since the fluctuation is so small. This of course ignores the thermal inertia of the earth. To see the effect of sun spots or lack of sun spots, we would need an extended period of high or low sun spot activity such as apparently happened during the little ice age. There are some indications that the years following 2008 will have low sun spot activity. If this is so, it will be interesting to see if this is a period of cooling.

3. If Carbon dioxide follows temperature rather than leading it, which is another pillar of the anti-anthropogenic model, one might also see a wave in the carbon dioxide readings with an 11 year cycle. Here, once again, the period might be too short to pick this up. However the global warming of the medieval period and the bronze age hipsithermal and the cooling of the little ice age not to mention the ice age from 11000 years ago and further back should be clearly visible in the carbon dioxide concentration in bubbles in the ice from these periods. If the medieval warm period was warmer than it is today, one would expect more than 380ppm of carbon dioxide in the bubbles in the ice from the appropriate years. Likewise, the little ice age should show low carbon dioxide , possibly less than the 280ppm preindustrial level. In all these periods, the sea surface temperature would have been of prime importance for the absorption or release of Carbon Dioxide. Oxygen isotope work on forams can give a good indication of the sea surface temperature to see if the sea was warmer during the medieval warm and bronze hipsithermal and colder during the little ice age. A confounding factor in the ice bubble record is that the upper 70 to 150m of the ice caps is not consolidated into ice and gas can diffuse down through this layer. This means that the gas in an ice core is more recent than the age of the ice. It also introduces a blurring of the record as air from different years mixes. This will make it hard to pick up short term changes in gas composition from ice cores but won't have such a blurring effect on longer warm or cold periods.

Whatever the final result of this debate, we must never allow science to become a religion. Science looses it power when people start to be dogmatic about their own pet theory and stop looking at the evidence. I have no idea whether global warming is all anthropogenic, partially anthropogenic or not anthropogenic at all. However, I do know that history is full of examples of very well thought of scientists who couldn't see the evidence that was in front of their own noses even when it was being pointed out by someone who had "seen the light". When continental glaciers were first proposed, the geologists of the time mocked the proponent of the theory and refused to see the evidence all around them. Continental drift was proposed centuries before it was finally accepted. Doctors, for the longest time, refused to wash their hands before doing operations or delivering babies even though they had just come from dissecting unpreserved corpses. Sometimes there was almost a hundred percent mortality of mothers and babies in maternity wards. This despite being told by proponents of antisepsis and the germ theory why they should wash their hands. Midwives had much better success at the time but the doctors had a motive for replacing midwives. Money. Always worthwhile to look at motive. And recently, despite strong evidence that lead is highly detrimental in any quantity, it was allowed to be put in our petrol, used to solder our tin cans and used in pipes. We mock the Romans for their use of lead glazes in their wine goblets and lead pipes in their water supply networks. Look at our own record. And even today, long after the publication of The origin of species, There are many who want to teach Intelligent Design instead of Evolution in our schools. Informed argument with open mindedness is the strength of science.

It is pretty important that we get it right. As mentioned above while many positive actions will likely be taken in the name of Anthropogenic Global Warming, not every action will be positive. On the plus side, if we reduce our use of fossil fuels by a shift to wind, solar and other renewables, this will reduce pollution and conserve these fossil fuels which are really far to valuable to burn. The planting of trees will stabilize soils and possibly help the hydrological cycle. This is all very positive and it doesn't matter whether it is done in the name of global warming or in the name of pollution control. However, if global warming is inevitable because it is part of a natural cycle, the money, effort and commitment we are now expending to reduce carbon dioxide emissions and even to sequester carbon would be better spent in working out ways to live with global warming. This could include developing new seed varieties, legislating against development within a certain vertical elevation from the sea, examining various health implications and so forth. Only slightly with tongue in cheek, we might be considering how we can get Iowa wheat farmers to grow rice and Eskimoes to grow wheat.

It is less damaging to falsely believe that global warming is not anthropogenic that to falsely believe that it is. If global warming is anthropogenic and we believe it is not, we will be preparing for the inevitable global warming. There is a very good chance that due to tundra carbon stores, clathrates and a number of other feed back mechanisms that we are over the tipping point; that a lot of carbon will be dumped into our atmosphere now no matter what we do. It is also very possible that we won't be able to persuade the various developing countries which are now undergoing logarithmic development to reduce their carbon emissions. If either of these scenarios are true and global warming is actually anthropogenic, our best strategy is to prepare for global warming rather than to try to sequester carbon. If we get it wrong the other way we will be putting wealth and energy into sequestering carbon which would be better spent preparing. Moreover, if it turns out after more research, that global warming is not anthropogenic, science, scientists and a lot of politicians are going to have a lot of egg on their faces. The public will loose faith in the validity of science. It will be much harder to persuade them that global warming is coming anyway and we should prepare for it. It will cut very little ice with them to explain that this is how science works; by having conflicting theories - by making predictions based on each theory and then testing which consequences are true.

What if we get it wrong, whether or not we are in for a sudden catastrophic climate change. If we believe the change is coming and get it wrong, we will have put in measures such as developing electric cars, installing wind turbines etc to reduce our release of fossil carbon into the atmosphere. Quite frankly, resources of coal and oil are far too valuable to be burning. They are feed stocks for a host of industries. Nothing much is lost.

If we believe that we are not in for sudden catastrophic climate change. That there will be climate change but it will be gradual and well within our capability to adapt to and get it wrong (in other words, sudden climate change does occur) we will likely have a world population of around one billion in a few decades. Not a bad thing for Gia but not so good for the 7 billion or so people who starve to death. All in all, I think it would be better to behave as if we are indeed in for sudden catastrophic climate change.

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