Posted by: erl happ | August 16, 2011

The character of climate change part 1

Figure 1 records global temperature as it runs between its minimum in January and maximum in July. Vital information is lost when we reduce the data stream to a computed mean (maximum plus minimum/2). But that vital information is retained in Figure 1.

Figure 1 Evolution of Global temperature from 1948 to early 2011 Source: http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl

Observations in relation to figure 1

  • The global maximum and minimum moved up and down for thirty years between 1950 and 1980 but without establishing a clear upward or downward trend despite the increase in so-called greenhouse gases over the period.
  •  After 1978 the minimum began to advance but not as fast as the maximum,
  • The minimum is much more volatile than the maximum.

The Earth is closest to the sun in January and this is the time when the ocean, most of it in the southern hemisphere, is best illuminated. The year-to-year variability in the January minimum is patently unrelated to ‘greenhouse factors’ that exhibit a monotonic increase over time. What causes this variation in the January minimum? A likely candidate is a variation in the degree of illumination of the southern oceans as cloud comes and goes. Cloud cover varies on a daily, seasonal, inter-annual and decadal basis. It varies on the scale of a human lifetime and longer.

Obviously we need to understand the forces that lie behind change in cloud cover. At this stage we don’t. We simply can’t rule out change in cloud cover as a cause of the change in global temperature.

How do we decide what is ‘good’?

The average between the daily maximum and the minimum is commonly reported as the ‘mean’. The mean temperature is averaged over the globe to derive the average temperature for the globe as a whole. A change in the mean can be due to change in minima or maxima. As is seen in figure 1 the maximum can change independently of the minimum.

For practical purposes it is the transition between the extremes that is important to agriculture, trade, commerce and human habitation. We find the extremes ‘remarkable’. However it is the length of the period of favorable weather between the extremes that determines whether plants will grow and mature well or poorly. The period of sunlight within the day influences the rate of photosynthesis and respiration. But, unless the air is warm plants will not grow. The same consideration applies when we consider the growing season as a whole. The mean temperature actually tells us very little about the habitability of the planet.

The UN panel on climate change was set up to assess whether man’s activities have influenced the climate of the globe. It was not asked to describe the natural forces that drive the temperature of the globe one way or the other. That was not part of the brief. The source of natural variation on inter-seasonal, decadal and longer time scales is still a mystery. When the panel reports that it cannot imagine what is causing the variation in the climate that we see (other than man) it is telling the story as it is. But, is the panel totally honest in suggesting that man is the culprit when it cannot describe the source of natural variation that is plainly there. If that source of natural variation can cause the temperature to rise and fall over a year or two, why not a decade or a century?

We need to discover the sources of natural variation so that we can expand the range of explanations for the change that we observe. It is desirable that we should not mistake one for the other, and like Don Quixote, go off tilting at windmills.

But, there is a more fundamental concern that relates to the efforts of the UNIPCC. It is this. The UN does not address the question as to whether the change in the climate that we see is advantageous or disadvantageous. It is the failure in this respect that represents the ongoing irrelevance of UNIPCC deliberations. The UN does not seem to be interested in the question that can be phrased in this way: OK, things are changing but does it really matter? Are we better or worse off?

Before leaving figure 1 lets note that the depression of maximum and minimum temperature from 1992-95 that is possibly related to the eruption of Mount Pinatubo. This is plainly an example of a ‘natural’ rather than a man made or ‘anthropogenic’ cause of climate variation.

What climate would we prefer?

At what temperature would the Earth be most productive? A temperature of at least 15°C is required to support plant growth and 25°C is about optimal. But, figure 1 indicates that the temperature of the air at the surface of the planet varied between just 12°C (the coolest average minimum) and 16° C (the warmest average maximum) between 1948 and 2010.

Were the temperature of the Earth to be the same at all latitudes and were there to be no variation at all (no seasons) the Earth would be quite unsuitable for human habitation. A regime that varied between 12°C and 16°C would very much inhibit the growth of many plants. It is the variation in temperature from warm at the equator and cold at the poles and the seasonal variation between summer and winter that opens the window for agriculture and animal husbandry. Birds migrate across the hemispheres because they need a daily food source and it is infrequently available on a year round basis within a single hemisphere. Man builds shelters and carefully conserves food so that he can eat in the lean times. Outside the tropics the lean times arrive with winter. It is the ‘larder’ the ‘pantry’, the ‘freezer’ and the ‘refrigerator’ that we hold nearest and dearest, a point that is well established in Kenneth Graham’s classic tale “The Wind in the Willows”. There has to be a time of the year when it is possible to actually grow the food and effective means to conserve it. That time of the year begins in ‘spring’ when animals emerge from their burrows after the winter hibernation and look around for something to eat.

So, we should begin with the obvious question “what is the nature of a ‘desirable climate’, where is it to be found, is it changing over time and is that climate improving or deteriorating ’? Are we happy to have a ‘winter’ or would summer be preferable? For that category of climates quite unsuitable for human habitation at any time of the year we might put aside any concern as to whether the temperature is increasing or decreasing as simply inconsequential.

The ‘global average’ is a statistic of little practical value especially if it is driven one way or the other by change in places that are uninhabitable  Similarly, the daily mean tells us nothing about how cold the nights are and how warm the days, nor the number of daylight hours in winter. We need to know more. Madrid has a much wider annual range of temperature than the isle of Capri. Which suits our purpose? If we seek to retire and write poetry under the shade of a tree the temperature requirement will be different to that if we wish to grow cherries that must experience a strong winter chill in order to set fruit.

Plainly such an approach increases the complexity of the analysis, but realistically, if we cannot answer these questions we are being hysterical rather than practical. Hysterical behavior is not adaptive. In former times it might have brought a slap around the head. Today it should bring a kindly arm around the shoulder and the polite query: What’s up dear? But, I do sometimes wonder whether the former approach is more appropriate if one is dealing with evangelical advocates who are plainly out of touch with reality. To people of this ilk I say, forget the mean, give me the raw data by latitude and longitude and I will try and make something sensible of it.

Where do people choose to live?

As an Australian I know that the early visitors to Australia were unimpressed. Much of Australia is desert and to this day most of the habitable country is seen as ‘marginal’. Australia supports little in the way of human habitation and is never likely to. This is one country that suffers extreme swings in weather and climate. When the rain falls the desert blooms and the inland rivers flow, and there is an enormous party of procreation. But for long periods it does not rain at all. Some coastal margins have a reliable rainfall and can support the growth of forests, but for a large part the desert runs close to, or all the way to the coast. The vegetation is hardy and Australians describe it as ‘the scrub’. The scrub can survive a run of bad seasons. In the early years in South Australia a notion was put about that ‘the rain follows the plough’, and for a while it seemed to work that way. But clearing of the Western Australian scrub started at the beginning of a long period of rainfall decline. Today, there seems to be no way back.

An intergalactic explorer, looking for greener pastures might not give Earth a second look. Humans are fond of their blue planet, but were it slightly warmer; it would be more productive. When Australians retire, even though they live in a continent that experiences warm summers, they move north because they don’t like winter. The grass may be green but it doesn’t grow much. It is just too cold. So, we must look at the pattern of human habitation as an indication of the manifest preference of the human species. Unlike bears, humans like to eat several times a day, every day of the year, so agricultural productivity is important. In pre-industrial societies gardening and food gathering were of pre-eminent concern. By and large, most of the globe is still pre-industrial and means of transport can be primitive so people tend to live close to where food can be easily obtained.

To some extent climate can be engineered, certainly within structures built by man, certainly in wealthy sophisticated industrial societies. Less naturally favorable climates can be tolerated if we can shelter ourselves from the extremes. Air conditioners are more numerous in China than anywhere. Mankind, by and large lives in India and China where the growing season is long, there is plenty of moisture and spring, summer and autumn favors plant growth, oftentimes in an environment that may be distinctly humid and a touch warm, certainly from the western European point of view. There is substance in the words of the song “Mad dogs and Englishmen go out in the midday sun” because the really productive parts of the British Empire were in climates rather warmer than experienced in the British Isles. That warmth made for a long growing season and high population densities.

Figure 2 Distribution of mankind on planet Earth

The map above indicates that human settlement is denser in humid, warm environments on the east coast of the major continents. South and East Asia are examples of locations eminently favorable for agriculture having abundant rainfall and a long growing season.   Western Europe defies the rule. But this part of the globe is unnaturally warm in relation to its latitude, particularly in summer, in part due to the influence of the warm North Atlantic Drift and also a persistent flow of tropical moist air from the south west. The growth of mining, commerce and manufacture and the development of cities and transportation promote a pattern of settlement different to that which existed in the agrarian past. Nowadays a lot of food is transported and stored for long periods increasing the range of climates that can support high population densities, so long as people can be kept warm in winter.

From figure 2 it is apparent that the densest areas of human settlement are to be found between latitude 10°south and latitude 60°north. But look at this. Figure 2 truncates a large part of the southern hemisphere. Why? Because, the missing portion experiences sub freezing temperatures over most of the year. The Southern hemisphere pole-wards of about 45°south has little land to support human habitation and pole-wards of 60° south comprises the giant, ever deepening  ice mound of Antarctica.

Why is it that the bulk of humankind is to be found between latitude 10° south and 60° north? It is because the land is more productive there. Life is easier. This is the message in figure 3.

Figure 3 The seasonal flux in temperature in degrees C in the more habitable latitudes

The habitable area of the northern and southern hemispheres experience very different thermal regimes. Which is to be preferred?

Agriculture is a seasonal activity. If temperature moves into the favorable range for long enough, farming is possible and so long as the food that is produced has an adequate ‘shelf life’, a larger population can be supported.  The more habitable latitudes of the northern hemisphere have the advantage over the southern hemisphere in this respect. Summer is warmer than it is in the southern hemisphere. At the height of northern summer, mean temperature approaches 25°C. In the warmest month the temperature is almost warm enough to promote the fastest rate of plant growth. This outweighs the disadvantage that northern winters are cooler than southern winters. Summer provides the bounty that maintains life and a relatively inhospitable winter is not a high price to pay if you are warm, well housed and well fed.

The most productive and most heavily populated parts of South and East Asia have a summer thermal regime that is even warmer than the global average. (Delhi India June Av Min 26.6, Av Max 39.3, Shanghai, China 24.9-31.3, Chongqing 25-34, Hanoi July 26.1-32.9). It is apparent that the warmest months of these locations are rather warmer than is optimal for photosynthesis. But the growing season is very long and this makes the land unusually productive. If the all the habitable lands of the northern hemisphere were as warm as East Asia productivity would increase with the length of the growing season. So, in this respect we can conclude that the warmest part of the globe, the northern hemisphere in summer, would be more productive if it were a little warmer. It is not warming that we should fear, but cooling.

A lesson in climate dynamics for the UNIPCC

Looking again at figure 3 we see that the pattern of seasonal change in ‘global temperature’ more strongly relates to the annual range in the northern hemisphere than the southern hemisphere. The extended annual range in the north is driven by the warming and cooling of the continental landmasses of Eurasia and North America in northern summer.

There is an interesting paradox here. In July and August, the globe as a whole is warmest. Paradoxically the Earth is actually 3% further from the sun in July than it is in March and September.  Solar irradiance is 7% less intense in July than it is in January. But atmospheric warming due to enhanced daytime radiation from warm land masses drives a loss of global cloud cover in mid year. Consequently the global average temperature is driven upwards to a strong peak in July-August. The strong rise in temperature in the northern hemisphere more than compensates for the cooling of the southern hemisphere in winter.

So, the surface is warmest when the Earth is furthest from the sun, in June, July and August. The lesson is plain. The level of irradiance from the sun is not the prime driver of surface temperature. It is the relative presence of cloud that determines the issue. Climate scientists that write IPCC reports maintain that cloud holds the heat in and amplifies the supposed heating effect of carbon dioxide. There is no shadow of doubt that the effect of cloud is to cool the earth, not warm it.

However, the fact that the southern oceans face the sun in January when the sun is closest and irradiance is 7% greater than in June, makes for a warmer globe because the ocean absorbs and stores energy rather than expelling it into the atmosphere from where it is pretty well lost to space within the 24 hour time cycle.

The Earth would be a lot cooler if the vast oceans of the southern hemisphere faced the sun when it was furthest away. Then the energy from the sun, when it is most abundant, would be expended on the land masses of the northern hemisphere and promptly returned to space. Due to the present happy conjunction of the tilt of the Earth’s axis, the orbital influence and the current distribution of land and sea one can conclude that the global climate is in a warm phase. The available energy when it is most abundant is safely delivered into storage in the southern oceans. The warmth from the sun is conserved for longer and the cooler areas of the globe benefit because the ocean currents (e.g. Gulf Stream) are warmer. It follows that the area of the globe that is currently suitable for habitation is larger than it would be if the sun were closest in June. We live in times that are favorable to mankind in a globe that is actually a little cool for maximum comfort. But we should note that the globe will cool as the orbit around the sun becomes less favorable.

It is apparent that surface temperature is much affected by the distribution of land and sea, orbital considerations and most of all, the relative abundance of cloud.

Were the orbit of the earth around the sun more elliptical than it currently is, the difference in irradiance between January and July would be greater. If the tilt of the axis were to be less than it currently is, the contrast between summer and winter would be less and higher latitudes would experience cooler summers.

If there were some factor that drives a variation in cloud cover when the bulk of the ocean faces the sun in December to March it would change the January minimum and the climate globally. With less cloud the globe would warm. With more cloud it would cool.

Plainly there is no variation at all in the area of the land masses of the northern hemisphere and this leads to little variation in the global maximum temperature in June-July. But there is obviously a large variation in cloud cover that causes the January minimum to swing wildly from year to year.

Does ‘climate science’ offer us an explanation for wide swings in the global minimum in January? Sadly, no! Climate science seems to be very closely focused upon the global average temperature and subtleties of this sort are un-remarked because un-noticed. This is like owning a car and not knowing whether the engine is in the front or the back.

If you went to your doctor and he insisted that the corns on the sole of your foot were related to the temperature of your inner ear you would probably seek alternative advice. If he said the corns could be related to the fit of your shoe you might be more inclined to listen. Similarly, a climatologist that observed that global temperature varied most dramatically in January and pointed to the clouds makes more sense than the guy who looks at the global average and points his finger at you suggesting that humanity is exhaling too much carbon dioxide, extravagantly using up scarce fuels and generally living too high on the hog.

Who is it that peddles this nonsense that the globe is in danger of getting too warm? Why are they doing it?

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