warming is the first in a series
of briefing documents investigating the indicators, science,
analysis and argument surrounding global warming.
One of a grouping of documents on global concerns at abelard.org.
|on energy||on global warming|
housing and making living systems ecological
sustainable futures briefing documents
|Tectonics: tectonic plates - floating on the surface of a cauldron|
|examples of macro-effects|
|macro and micro studies|
|albedo—Lovelock’s daisy planet|
|using earthshine to improve understanding of global warming|
|planetary heat circulation|
|dust, aerosols and particulates|
|carbon in the atmosphere|
|where is the missing carbon?|
|is water vapour a greenhouse gas?|
Here are a series of items that summarise current arguments concerning global warming. They present various points of view and some of the basic problems in following the science. Keep in mind that the concept of global warming involves the study of an immense and very complex system. While the general consensus is that global warming is occurring and is in part caused by human activity [anthropogenic], anyone who tells you that global warming is understood and proven (or disproven), followed by some trite reason, simply does not understand the situation.
The first two items are 2003 reports on macro-climate.
Macro-weather attempts to understand the big systems , whereas micro-weather concerns the weather forecasts that are broadcast regularly around the world. The maths of short-term weather forecasting is well understood and has been since 1922 . The accuracy of weather forecasts relates to the number of local readings that can be taken (cells) and the amount of computing power that can be applied to these measurements. Current weather forecasting is usually attempted four or five days ahead, with its accuracy rapidly falling off.
Global warming concerns understanding the macro-system, such as the why and wherefore of the current observed increase in planetary atmospheric temperatures. The current tentative consensus is that global warming is a reality, but it is uncertain how much this is caused by human activity or other factors.
The macro-weather is being investigated by assembling experimental models of the weather system on computers. Experimental results are fed in and the results predicted by the model are then checked against weather records and various means of investigating past planetary conditions, for instance: the width of rings in trees, which grow differentially according to the year’s weather, and analysis of ice cores for items such as dust, pollen and thickness (precipitation per year). The models are then continually adjusted in attempts to make them come more into accord with reality, as new data are discovered, and as we gain understanding of new mechanisms.
Note, that even if the model does reasonably predict known events, we still cannot know whether it is predicting these events for the ‘right’ reasons or by chance. Only as we predict ‘new things’ with the models and they keep coming out right, will confidence in the models grow.
albedo—Lovelock’s daisy planet 
This illustration was developed by Lovelock to show how life could effect the conditions on a planet without any necessary assumption of ‘intelligence’.
Planet Daisy is very basic. Everywhere you go, the bare ground of Daisy has an albedo of 0.4. That means, that the planet surface reflects about 40% of incoming sunlight. Then the planet is seeded with daisies, which range from dark to light. (Daisies cannot grow below 5°C or above 40°C, in fact, their favourite temperature is about 20°C.) The darker daisies have an albedo of 0.2; while for the lighter daisies, the albedo is around 0.7. Planet Daisy starts to warm up from the sun. When the temperature reaches 5°C, the daisies start to grow.
The dark daisies will have an advantage. They will absorb more warmth and grown faster than the lighter daisies. As increasingly the dark daisies cover the ground, Planet Daisy becomes warmer from all the heat absorbed by the dark daisies.
In time, the planetary temperature reaches 20°C. Now, the light coloured daisies have an advantage—the dark daisies are absorbing too much heat, whereas the light daisies are doing just fine. So the light daisies spread. Because they are reflecting more heat, the light daisies protect the planet from becoming too hot. This is a negative-feedback system which will tend to regulate the planet’s temperature. For, if the light daisies colonise too much land, the planetary temperature will drop.
Our planet is more complex, but its temperature is similarly effected by clouds, by ice fields and darker oceans. If the ice fields melt, the Earth will absorb more heat. More heat will increase cloud formation, and so on, rather like on Planet Daisy. Note that plant life takes up carbon from the air, a component of the greenhouse gas, carbon dioxide.
earthshine to improve understanding of global warming
See also this science news item: rapid climate change in alaska, with comments on climate models
The atmospheric temperature of the Earth is in an approximately stable state as incoming heat from the sun is, in turn, reflected out into space, maintaining an income-outflow energy balance. For more on the physics and chemistry of the atmosphere, see below for greenhouses gas load and effects; and for spectral effects, see How atmospheric chemistry and physics effects global warming.
Be careful to note that this energy balance diagram is very much a matter of planetary averages. Note the difference between the 343 Watts per square metre average [343 W/m²] shown in this diagram and the 1,000 W/m² in direct sunlight. Refer to the albedo figures above and the insolation discussion in Photovoltaics (solar cells) for a better understanding.
And from an ongoing discussion:
The long and the short of it is that our knowledge of the effects of dust in the atmosphere is so far rudimentary. This article covers the notion of catastrophic levels of dust in the atmosphere, among other broad categories of ecological threats. (The article starts part-way down the page, which page is written in poor html.)
An aerosol is an airborne stable suspension of solid or liquid particles or both.
Aerosol characteristics: an aerosol’s lifetime depends on particulate type and size.
Various characteristics of aerosol particles are discussed here: fine & coarse particles; sulphates, nitrates, together with notes on some consequent meteorological effects, like smog.
Some suggest that global warming is considerably greater than registered, but is heavily offset by global dimming.
Key terms in global dimming:
The desert surface being broken, so allowing the release of sand and dust, is also a problem in war zones, such as Iraq, when there is heavy tank and other traffic going cross-country.
The general consensus is that the massive build up of CO2 in the atmosphere is dangerous and a factor in global warming. The system of carbon recycling is very complex. A useful diagram can be found here.
While the link between CO2 and global warming is not yet fully established, it is the leading explanation we have for the known facts. It is a theory, but not a well-tested one like gravitation or evolution by natural selection, neither can we fully or sanely test it in the real world by waiting until the CO2 reaches potentially dangerous levels.
The current concentration of carbon dioxide in the atmosphere is approximately 390 parts per million - higher than it has been for at least the past 430,000 years. (1850: 250 ppm; 2010: 390 ppm.)
The seasonal carbon dioxide concentration varies from place to place on the planet. For example, from the graph above, the CO2 peaks are in April and May with the troughs in July; but as you can see the general trend is upwards. Growing plants in the new growth season offset the release of CO2 into the atmosphere from decaying vegetation that occurs outside the growing season.
In the next 100 years, unless immediate action is taken, carbon-dioxide levels could rise to between 800 and 1,000 parts per million. The last time carbon dioxide was that high was during the Eocene. The Eocene epoch is part of the Tertiary Period in the Cenozoic Era, and lasted from about 54.8 to 33.7 million years ago (mya).
At that time Antarctica was a pine forest and sea level was at least 300 feet higher than today.
|carbon dioxide in the atmosphere, as billions of tonnes per year|
Total anthropogenic CO2
|CO2 from fossil fuels||CO2 from deforestation||Sequestered CO2||CO2 remaining in atmosphere|
|2004||8 billion tonnes||6.5 billion tonnes||1.5 billion tonnes||5 billion tonnes||3 billion tonnes|
|2035||12 billion tonnes|
It is believed that the earth’s atmosphere originated about 4 billion years ago with gases released by volcanic activity. These gases included water vapour, carbon dioxide, chlorine and sulphur compounds, together with methane, nitrogen, and ammonia. More nitrogen may have been formed by light enabling the breakdown of ammonia (NH3).
Next, the water vapour condensed, making the oceans, while the carbon dioxide reacted chemically with substances in the earth’s crust. This CO2 is still fixed in the oldest sedimentary rocks. Of the original atmosphere’s components, nitrogen is the only one now remaining in high concentration: 78 percent.
About 3.5 billion years ago, lightening caused oxygen to disassociate [separate] from water [H2O] to become free atmospheric oxygen. By 0.5 billion years later [3 billion years before present], oxygen was relatively plentiful, but not enough for humans to be able to breathe. It was only during the Carboniferous period, with its extensive coal-forming swamp forests, about 360 million years ago, that photosynthesis released sufficient oxygen that its concentration became closer to today’s. At that time, much carbon-containing plant matter fell to the ground, was buried and became coal.
Thus, by 100 to 200 million years ago, when the dinosaurs lived, atmospheric oxygen concentration was about 35 percent. This oxygen level continued probably until 65 million years ago when it is generally thought that an enormous meteorite collided with the earth, with consequent fires removing most of the forests. Nowadays, with lower rates of photosynthesis, the oxygen content of the atmosphere is about 21 percent.
[Note: the large herbivore dinosaurs were able to evolve thanks to abundant food provided by the forests and swamps, and to the ample oxygen supply, necessary for such large bodies. The giant carnivore dinosaurs evolved because an abundant food supply composed of herbivore dinosaurs. The dramatic meteor strike destroyed both the dinosaurs’ food and their oxygen supply.]
It is known that the carbon dioxide level before 1850, and the advent of the industrial revolution in the West, was about 27 percent lower than today, that is about 260 parts per million [ppm]. It is also known that the CO2 level was about 18 percent lower in the 1970s, or about 295 ppm. Notice how the ppm of CO2 is rising at an increasing rate.
At the end of the 19th century, there was approximately 280 parts per million of carbon dioxide in the atmosphere. At the end of the 20th century, this is approximately 360 ppm—an increase of 25%. Estimates using current trends suggest that CO2 will be anything between 450 and 950 (!) ppm by the end of the 21st century.
|carbon dioxide in the atmosphere, as parts per million|
|Parts per million of CO2 in atmosphere||170||260||280||295||360||future estimates||450-900|
|Annual increase||+ 1.5 ppm per year||future estimates||+ 6 ppm per year|
However, there are possibilities the build-up will go far faster than these figures, as positive feedbacks may occur—for instance, the rising temperature may melt permafrost and release vast quantities of tied-up CO2 into the atmosphere. There are already areas of permafrost giving way in Alaska. The northern latitudes of the world are home to the greatest area of forestry on the planet, known as the boreal forest. In Alaska, the boreal forest is showing increasing stress, as insects probably  are extending their range and killing great areas of forest. It is entirely possible that the ecology will not be able to keep up with the rate of change, and that the boreal forest will die out.
The boreal forest, which is about 17% of the planetary land mass, and the tropical forests are unlikely to take up much carbon because they are already in a steady state, giving out as much carbon as they absorb. Much more likely is the danger they will release what they already tie up.
It is estimated that, at present, human activities are pumping around 8 billion tonnes of carbon into the atmosphere every year, with around 5 billion tonnes being sequestered  in forests and the oceans. Thus, each year a surplus of 3 billion tonnes is estimated to stay in the air to contribute to warming effects.
Woodlands act as a sink for carbon, tying up huge quantities around the planet. Humans are currently extending planting greatly and this is probably mitigating the worst effects of the carbon build up. But this is a self-limiting process. As the woodlands become mature, they start to return as much carbon to the atmosphere as they soak up. If and as that occurs, the rate of atmospheric burden will probably climb more rapidly.
Of the 8 billion tonnes pumped into the atmosphere each year, 5 billion tonnes are from fossil fuels as we burn the results of millions of years storage in a few decades. The remainder is from deforestation. Globally, CO2 is rising at about 1.5 parts per million each year.
The estimate for carbon dioxide production in 2035 is for about twelve billion tons per year. If the sink rate  does not increase beyond the present 6.5 billion tonnes per year, that will mean the ppm [parts per million] quantity will be climbing nearly 4 times as fast per year in only 30 years time, on that basis alone!
A considerable environmental puzzle until recently has been, “where is the missing carbon?”
This has now been answered by two related studies reported in NatGeo.
What effects does this have on the oceans? In a related study, it is said that ocean acidity is rising (CO2 is an acidic gas).
To understand increasing carbon emissions it is essential to realise that the known carbon sinks have a strictly finite ability to absorb the carbon going into the atmosphere. In the above article is the following:
This limitation also applies to the uptake by land-based plant life. For example, as a forest become mature it goes into carbon balance; that is, it sends about as much carbon back into the atmosphere through the rotting down of old leaves and fallen trees as it absorbs. One of the major reasons that the situation has not been becoming worse at a faster rate is due to much reafforestation around the world.
The quantity of CO2 in the earth’s atmosphere is now higher than it has been in almost 2 million years, a time when temperatures were considerably warmer than now.
Present estimates suggest that the Earth could face a temperature rise ranging from 1.8 to 6.3 degrees Fahrenheit, but the best guess is for a rise of 3.5 degrees F. However, if the carbon dioxide levels do not stabilise, a temperature rise of between 15 to 20 degrees F is considered possible.
Over the last century [1901-2000] there has been an increase of about 1° Celsius/ 1.8° Fahrenheit in global average temperatures. To most people a 1°C/1.8°F rise seems very insignificant, but it really does have large implications. In 1816 (‘the year without a summer’, attributed to a large volcanic eruption), the world experienced slightly less than a 1.8°F/1°C loss in temperature because of a volcano eruption. During the course of 1816, there was frost in New England in July, worldwide crop failures and many other problems relating to the very small drop in average temperatures. There is more on volcanoes and weather here.
From Year Without A Summer, and with a great deal of contemporary detail from the New England area.
(Article worth a scan.)
Between 12,000 and 11,000 years ago, towards the end of the last ice age, sea levels rose by between 100 to 140 metres when the Fennoscandia ice sheet melted rapidly. There was a similar fast melting of the Laurentide ice sheet between 8,000 and 5,000 years ago. These large conversions of ice to water changed the face of the Earth, with events like the continents of Asia and North America being separated by the appearance of the Bering Straits. Overall, the global sea level rose an average of 1 metre a century until 2,500 years ago.
Today, there is enough water tied up in the south polar cap , and in glaciers, to raise water levels by about 70 metres if this is all melted. Global warming would also result in expansion of water volume by heat.
However, because average temperatures in the Arctic and Antarctic are well below 0°C, the melting point of ice, such a scenario is not likely in any foreseeable near future.
A general prediction of global warming does not just suggest that there will be an average higher world temperature. It also proposes that there will be greater variations in temperature with more extremes of local heat and cold, higher or lower precipitation, more storms and more droughts. There are also fears that ocean circulation systems may already in process of modification.
The amount of heat reflected into space will lessen if greenhouse gases in the atmosphere increase in quantity. This will raise planetary atmospheric temperatures until a new balance of income-outflow energy is achieved.
To obtain some idea of the contribution of various atmospheric gases to the greenhouse effect, study the following table:
As some of these gases are in the atmosphere prior to human activity, we now narrow down this data to show the relative estimated effects of human contributions [data for this table derived from Third assessment Report, Climate Change, 2001]. To keep things in proportion, see also end note 9 and note 3 :
Here is another item, again from NASA, that attempts to assess future changes under lack of action or action. Note carefully that, in this case, the reference is to a model attempting to predict the future, always a fraught enterprise.
It has been suggested by Rowing that the symptoms of global warming, that is increases in gas concentrations (particularly water vapour), could as easily be a symptom as they could be a cause. That is, heating could cause a rise in atmospheric gases, or a rise in those gases could cause an increase of heat.
Water vapour is a variant case. The concentration of water vapour in the atmosphere increases rapidly as temperature increases: about 6% per 1°C. This amounts to a strong positive feedback system. Thus, increases in temperature instigate increases in atmospheric water vapour, which, in turn, increase greenhouse effects and thus lead to further increased warming. [For much greater detail on feedback, see Feedback and crowding.]
There is little doubt now that some atmospheric heating is occurring, but some suggest that sun activity may be a main driver, while yet others wonder if there is some of both increased sun activity and human-driven warming.
It is also likely that the NASA report is rather hyped, this PDF maybe the original study for that report. The item has plenteous references for those wishing to dig still deeper.
Increases in forcing caused by greenhouse gases between 1750 and 1998 were estimated as 2.48 W/m² (IPPCC3). It is estimated that an increase of 3.3 W/m² results in 1°C warming. The estimate is that so far the rise is approximately .75°C. There are various guesses that these amounts of warming will set off positive feedbacks (or even at a stretch, negative feedbacks). The guesses I have seen tend to suggest that these feedbacks would be about two to four times the originating forcings by the greenhouse gases (GHGs). As these feedbacks can happen over long time periods, it may well be that rises above 2°C are already in the pipe-line. Thus, political talk about restricting rises to 2°C must be treated with some caution.
|is water vapour a
I have seen various comments suggesting global warming cannot be caused by carbon dioxide (anthropogenic warming) because water vapour is a much more important greenhouse gas.
The argument against this is complex.
The relevant search term is ‘atmospheric chemistry’. The following books look interesting:
Atmospheric Chemistry and Physics : From Air Pollution to Climate Change is 1300 pages and costs in the region of $100! depending on your source. The book looks the most interesting I have discovered so far..
Chemistry of Atmospheres: An Introduction to the Chemistry of the Atmospheres of Earth, the Planets, and Their Satellites is about half the size and a quarter of the price.
I have located various attempts on the web which I find none too clear. Here is the best one so far found.
The argument runs thus:
See also “Water vapour much magnifying temperature increases over Europe” [news-lite]
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|Related further documents|
1 Replacing fossil fuels—the scale of the problem
2 Nuclear power - is nuclear power really really dangerous?
3 Replacements for fossil fuels—what can be done about it?
3a Biofuels 3b Photovoltaics (solar cells)
3c tar sands and shale oil
5 Energy economics—how long do we have?
6 Ionising radiation and health—risk analysis
7 Transportable fuels 7a Fuel cells
8 Distributed energy systems and micro-generation
9 Fossil fuel disasters
10 books on energy replacements with reviews
|On global warming
4 Global warming
4a Anthropogenic global warming, and ocean acidity
4b energy pricing and greenwash
4c How atmospheric chemistry and physics effects global warming
4d Antarctica melting ice, sea levels, water and weather implications
email abelard at abelard.org
© abelard, 2003,22 august
the address for this document is http://www.abelard.org/briefings/global_warming.php