global warming

a briefing document

Global 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
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 Non-pv (photovoltaic) solar technology sustainable futures briefing documents	3d Tar sands and shale oil 3e Wind power 4 see Global warming section on right 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 On housing and making living systems ecological		8a Geothermal systems and heat exchangers 8b Combined energy systems 8c Energy storage 9 Fossil fuel disasters 10 Fossil fuels are a dirty business 11 There she blows! striking oil 12 Books on energy replacements with reviews Tectonics: tectonic plates - floating on the surface of a cauldron	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 4e Gathering data to test global warming 4f Arctic melting ice, sea levels 4g Shifting global and local weather patterns 4h Dendroclimatology

Index
examples of macro-effects
macro and micro studies
albedo—Lovelock’s daisy planet: using earthshine to improve understanding of global warming
planetary heat circulation sun effects
dust, aerosols and particulates: global dimming


carbon in the atmosphere: where is the missing carbon?
temperatures
water levels
weather
historic data
greenhouse effects
is water vapour a greenhouse gas?
end notes

site map

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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.

examples of macro-effects

ocean circulation and rapid climate change [2003]

“The researchers argue that understanding the mechanisms underlying past climate change events is increasingly important as people grow more concerned about the magnitude and rate of future climate change.”
—
“The 'superflood' was enough to alter ocean circulation in the Northern Hemisphere: analysis of ice cores taken in Greenland reveal that for the next 200 years or so, the mean temperature dropped by 5°C, snow accumulation decreased sharply and forest fires became more frequent.”

“During the last Ice Age, when a kilometres-thick ice sheet covered most of Canada and parts of the northern United States, armadas of icebergs were episodically launched into the North Atlantic. The melting of this freshwater ice and the associated freshening of ocean surface waters are believed to have changed the strength of the oceanic thermohaline circulation, thereby causing abrupt climate changes," they said.”

yet another step in understanding the macro-climate [2003]

“Scientists using data from a NASA satellite have found another piece in the global climate puzzle created by El Niño. El Niño events produce more of a steady rain in the middle of the Pacific Ocean. This is important because whenever there is a change in the amount and duration of rainfall over an area, such as the central Pacific, it affects weather regionally and even worldwide.”

With images, graphs and more.

macro and micro studies

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 [1]. 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 (see also How atmospheric chemistry and physics effects global warming). 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 (dendrochronology), 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 [2]

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.

Earth albedo is approximately 0.9 for ice fields, 0.2 for earth/soil/vegetation and up to 0.1 for oceans and clouds (whole planet average: 0.3).

using earthshine to improve understanding of global warming
with illustrations.

“ Though not fully understood, the shifts may indicate a natural variability of clouds, which can reflect the sun's heat and light away from Earth. The apparent change in the amount of sunlight reaching Earth
in the 1980s and 1990s is comparable to taking the effects of greenhouse gas warming since 1850 and doubling them. Increased reflectance since 2001 suggests change of a similar magnitude in the opposite direction.”
—
“ At the moment, the cause of these variations is not known, but they imply large shifts in Earth's radiative budget [...].”
—
“ The research offers evidence Earth's average albedo varies considerably from year to year, and from decade to decade. "Our most likely contribution to the global warming debate is to emphasize the role of clouds in climate change must be accounted for, illustrating that we still lack the detailed understanding of our present and past climate system to confidently model future changes, [...]. ”

Earthshine details and photos.

See also this science news item: rapid climate change in alaska, with comments on climate models

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planetary heat circulation

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.

Diagram showing the evolution of greenhouse effects on our planet. Image credits: UNEP & GRID-Arendal
Image credits: UNEP & GRID-Arendal

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:
here is a short item discussing the basics of atmospheric circulation, with pictures! This item is part of a series of lecture notes on atmospheric chemistry.

Other related pages are
Climate change 1 2
Los Angeles smog 1 2
Ozone and ozone destruction

sun effects

recent history of the sun

“Since the middle of the last century, the Sun is in a phase of unusually high activity, as indicated by frequent occurrences of sunspots, gas eruptions, and radiation storms. Researchers at the Max Planck Institute for Solar System Research (MPS) in Katlenburg-Lindau (Germany) and at the University of Oulu (Finland) have come to this conclusion after they have succeeded in reconstructing the solar activity based on the sunspot frequency since 850 AD.

combining historical records and ice core measurements

“To this end, they have combined historical sunspot records with measurements of the frequency of radioactive isotopes in ice cores from Greenland and the Antarctic. [...] Since 1940 the mean sunspot number is higher than it has ever been in the last thousand years and two and a half times higher than the long term average. The temporal variation in the solar activity displays a similarity to that of the mean temperature of the Earth. These scientific results therefore bring the influence of the Sun on the terrestrial climate, and in particular its contribution to the global warming of the 20th century, into the forefront of current interest.

the sun’s influence

“However, researchers at the MPS have shown that the Sun can be responsible for, at most, only a small part of the warming over the last 20-30 years. They took the measured and calculated variations in the solar brightness over the last 150 years and compared them to the temperature of the Earth. Although the changes in the two values tend to follow each other for roughly the first 120 years, the Earth’s temperature has risen dramatically in the last 30 years while the solar brightness has not appreciably increased in this time.

“The German-Finnish research team has now applied a new method to obtain insight into the development of the sunspot number from before the beginning of direct records. In addition, these experts have analyzed measured abundances of beryllium-10 in ice cores from Greenland and the Antarctic. This radioactive isotope is created when energetic particles in cosmic rays enter the Earth’s atmosphere and split atomic nuclei of nitrogen and oxygen. Beryllium-10 (half-life 1.6 million years) is a product of this decay process, which is then washed out of the atmosphere by precipitation and then deposited in layers in the polar ice fields. Since the cosmic rays are partially deflected by the solar magnetic field filling interplanetary space, the production rate of Beryllium-10 in the atmosphere varies with the strength of this magnetic field, which in turn is associated with the number of sunspots. [...]”

conclusion:
recent increases in the earth’s temperature are due to the greenhouse effect caused by carbon dioxide

“These findings bring the question as to what is the connection between variations in solar activity and the terrestrial climate into the focal point of current research. The influence of the Sun on the Earth is seen increasingly as one cause of the observed global warming since 1900, along with the emission of the greenhouse gas, carbon dioxide, from the combustion of coal, gas, and oil. "Just how large this role is, must still be investigated, since, according to our latest knowledge on the variations of the solar magnetic field, the significant increase in the Earth’s temperature since 1980 is indeed to be ascribed to the greenhouse effect caused by carbon dioxide," says Prof. Sami K. Solanki, solar physicist and director at the Max Planck Institute for Solar System Research.”

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dust, aerosols and particulates

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.

warmer and wetter, or warmer and dryer

“The haze is reducing sunlight to the oceans and one of the things sunlight does is evaporate water from the ocean which gives us rain in the water cycle," he said.

“He said recent research by his team in an agricultural plain running across north India near the Himalayas showed that 10 to 17 percent of sunlight was not reaching the ground.”

is soot a greater factor in global warming than previously supposed?

"Grains of soot deposited in snow have also caused about one-quarter of the observed rise in global surface temperature since 1880, suggests the model by James Hansen and Larissa Nazarenko. The pair examined how soot particles affect the atmosphere when they darken snow and ice.”
—
“ Fresh snow reflects more than 90 percent of incident light - both the organic and black-carbon components of soot increase its absorption. Local soot concentrations in snow vary widely, but Hansen estimates that it reduces light reflection by 1.5 percent in the Arctic and by 3 percent over land in the Northern hemisphere.

“The extra absorbed energy helps melt snow and ice. This creates positive feedback - and speeds melting - because wet snow absorbs more light than dry snow, and liquid water absorbs about 90 percent of the incident light.”

global dimming

Some suggest that global warming is considerably greater than registered, but is heavily offset by global dimming.

“NARRATOR: Germany, Israel, what about the rest of the world? Working independently of each other, Liepert and Stanhill began searching through publications, journals and meteorological records from around the world. And they both found the same extraordinary story. Between the 1950s and the early 1990s the level of solar energy reaching the earth's surface had dropped 9% in Antarctica, 10% in the USA, by almost 30% in Russia. And by 16% in parts of the British Isles. This was a truly global phenomenon, and Gerry gave it a suitable name - Global Dimming. But again, the response from other scientists was one of sheer disbelief.”
—
“NARRATOR: In the polluted air billions of man-made particles provided ten times as many sites around which water droplets could form. So polluted clouds contained many more water droplets, each one far smaller than it would be naturally.** Many small droplets reflect more light than fewer big ones. So the polluted clouds were reflecting more light back into space, preventing the heat of the sun getting through. This was the cause of Global Dimming.”
[Quoted from bbc.co.uk January, 2005]

[The above article claims that smaller drops lead to less rain.
This article is recommended reading: ]

Key terms in global dimming:

pan evaporation rate -

the evaporation rate from a pan, which is checked each morning, the evaporation rate being assessed by how much water must be added to return the water level to that of the previous morning.
temperature variation, that is the day-night difference.

global dimming or global brightening! is dust countering global warming?

“Michael Roderick and Graham Farquhar from the Australian National University in Canberra found that evaporation rates across Australia, measured using continually replenished pans of water, have fallen significantly over the last 30 years, a sure sign that less direct sunlight is reaching the surface. The decline matches the effect seen in the northern hemisphere. "This proves that it is a global phenomenon," says Roderick.”
—
“Burning fossil fuels not only increases carbon dioxide levels in the atmosphere; it also pumps tiny particles into the air. Meanwhile higher temperatures increase the amount of cloud cover. The clouds and particles help to block the Sun's rays, and the scattered light they allow through actually boosts plants' absorption of carbon dioxide, the principle greenhouse gas.”

growing problems with dust storms

“The problem is far worse than previously believed, he says after studying 50-years-worth of global satellite imagery.

“A major cause, he says, is the increasing use of four-wheel drive vehicles to replace camels to cross the deserts. "Toyota-isation" - a term Goudie coined to describe the constant desert journeys made by Toyota Land Cruisers - is scarring the desert’s protective surface layer, releasing dust into passing winds. "If I had my way, I would ban them from driving off-road," he said.

“ "The desert surfaces have been stable for thousands of years because they usually have a thin layer of lichen or algae, or gravel from which the fine sand has blown away. Once these surfaces are breached you get down to the fine sand again, which can be picked up by the wind," Goudie explains.”

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.

carbon in the atmosphere

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.)

increase in atmospheric carbon dioxide, 1955-2011
From the IPCC Fifth Assessment Report 2013 Summary for Policymakers [previous Reports - links]
“The atmospheric concentrations of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years.
CO₂ concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions.
The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification...”

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
present	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
future estimates
2035	12 billion tonnes

short history of the earth’s atmosphere - draft

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 is a non-toxic gas. It has beneficial uses and is the "fizz" in carbonated beverages. When frozen, it is "dry ice". At concentrations of from 2,500 ppm to 5,000 ppm carbon dioxide can cause headaches. At extremely high levels of 100,000 ppm (10 percent) people lose consciousness in ten minutes, and at 200,000 ppm (20 percent) CO₂ causes partial or complete closure of the glottis.”

It has been said that we are running a car with the garage door closed.

carbon dioxide in the atmosphere, as parts per million
Year	past	pre- 1850	1900	1970s	2000	present	2004	future estimates	2100	2035
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 [3] 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 [4] 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 [5] 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!

Where is the missing carbon?

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.

“Since mass consumption of fossil fuels began with the industrial revolution around 1800, the concentration of carbon dioxide in the atmosphere has grown from an estimated 280 parts per million to around 380 parts per million.”
—
“Their results suggest that the oceans have taken up 48 percent of all carbon dioxide emitted from fossil fuel burning and cement manufacture (a major source of the gas) between 1800 and 1994.”

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).

“If predictions made by Feely's team are right, the surface of oceans - where most marine life is found - could soon become more acidic than they have been in five million years.

“This increase in acidity makes it difficult for shell-forming animals and some algae to amass carbonate ions from the seawater to form their calcium carbonate shells.

“Corals, some types of mollusk, and tiny planktonic organisms called foraminifers and coccolithophorids could all be affected. Many of these species form key links in the marine food chain.

“Past studies have shown that at atmospheric carbon dioxide concentrations of 700 to 800 parts per million - which some scientists say could be reached by the end of this century - the rate at which these organisms can form shells could be reduced by as much as a 25 to 45 percent.”

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:

“According to the study by Sabine and his colleagues, the amount of carbon dioxide the oceans have currently taken up is about a third of what they can hold. After that, the researchers warn, the rate of global warming could accelerate.”

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.

temperatures

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.

“The most likely cause was volcanic influences. Proponents note that a number of major volcanic eruptions preceded 1816: Soufriére and St. Vincent in 1812: Mayon and Luzon in the Phillippines during 1814; Tambora in Indonesia during 1815. The volcanic theory of climatic influence relates increased volcanic activity with decreased temperatures due to the increased reflection of solar radiation from volcanic dust blown and trapped high in the atmosphere. The Tambora eruption has been estimated to be the most violent in historical times. The explosion is believed to have lifted 150 to 180 cubic kilometres of material into the atmosphere. For a comparison, the infamous 1883 eruption of Krakatau ejected only 20 cubic kilometres of material into the air, and yet it affected sunsets for several years after.”

various technological fixes have been suggested to mitigate anthropogenic global warming (agw)

(Article worth a scan.)

“Scientists have previously estimated that reflecting less than 1% of sunlight back into space could compensate for the warming generated by all greenhouse gases emitted since the industrial revolution. Possible techniques include putting a giant screen into orbit, thousands of tiny, shiny balloons, or microscopic sulphate droplets pumped into the high atmosphere to mimic the cooling effects of a volcanic eruption. The IPCC draft [January 2007] said such ideas were "speculative, uncosted and with potential unknown side-effects". ”

water levels

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 [6], 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.

Estimates for rising sea water suggest that:

during 1901 – 2000 sea level rose: 9 cm (4 inches);
a predicted sea level rise for 2001 – 2100: 9 to 88 cm (4 to 40 inches).
There is a considerable range of future estimates.
if the Greenland ice sheet melted, add 6.75 metres (25 ft);
if the West Antarctic ice sheet melted, add 4.3 metres (16 feet).
The melting of these ice sheets would be enough to flood Florida and Bangladesh.

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.

related material
NASA GCMD Learning center: Is sea level rising? With graphs and useful links.
The essential guide to flood planning and preparation (UK-based)

weather

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.

Historic data

actual and predicted temperature change - graph 1850-2000 alleged mid-twentieth century global cooling

“The mid-20th-century blip turns out to have been the consequence of another by-product of human activity: sulphur and other airborne particles that bounce back sunlight before it can hit the Earth, thus offsetting the greenhouse effect. By the late 20th century, efforts to control that sort of pollution were having an effect. The particulate content of the atmosphere was falling, and the world began to heat up once more. The idea of global warming was retrieved from the bin and turned into one of the biggest arguments of our time.”

greenhouse effects

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.

Here is a counter-claim to the notion of increased greenhouse effects:

“From the foregoing, we can safely disregard the media hysteria about this paper's [Nature v.410, p.355, 15 March 2001] findings. At face value it proves little that we did not already know. The `increase' in the greenhouse effect claimed was mostly caused by a real or imagined change in the methane spike at wave 1300, not by CO₂.”
—
“And even if we accept the `statistical significance' of the two gases identified as showing the greatest effect, namely methane and the CFCs, neither gas can be considered as problems at the present time. Methane has now stopped increasing, while CFCs are already in decline due to the restrictions of the Montreal Protocol.

“The primary gas at the centre of the greenhouse controversy - CO₂ - gives only weak indications in this study, well within the range of instrument error between two very different instruments separated by technologies 27 years apart.”

Despite the rhetoric of this document and the reasonable criticism of the quoted paper, note the words “this paper”.

gases in the earth’s atmosphere
gas		formula	percentage	parts per billion
nitrogen		N₂	78%	780,000,000
oxygen		O₂	20.6%	206,000,000
other gases			1.4%	14,000,000
	argon	Ar	0.934%	9,340,000
	water vapour (var.)	H₂O	0.4%	4,000,000
	carbon dioxide	CO₂	0.035%	350,000
	neon	Ne	0.001 82%	18,200
	helium	He	0.000 524%	5,240
	methane	CH₄	0.000 15%	1,500
	krypton	Kr	0.000 114%	1,140
	hydrogen	H2	0.000 05%	500
	nitrous oxide	N₂O	0.000 03%	300
	ozone	O₃	0.000 005%	50
	fluorocarbons	xFC	0.000 000 1%	1
key:	= greenhouse gas

To obtain some idea of the contribution of various atmospheric gases to the greenhouse effect, study the following table:

greenhouse gas		lifetime in the atmosphere, in years	global warming potential (GWP) after 100 years	gas in earth’s atmosphere (parts per billion)	relative contribution to global warming [7]
CO₂	carbon dioxide	indeterminate	1	350,000	73%
CH₄	methane	14	21	1,500	7%
N₂O	nitrous oxide	~ 200	310	300	19%
others [8]	fluorocarbons	45 – 1,700	140– 11,700	1	1%
Note that greenhouse gases with longer lifetimes accumulate more GWP with time.

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 :

greenhouse gas (GHG)		lifetime in the atmosphere, in years	global warming potential (GWP) after 100 years	percentage of this GHG from human sources	relative human contribution [7]
CO₂	carbon dioxide	indeterminate	1	30+%	60%
CH₄	methane	14	21	70% [10]	20%
N₂O	nitrous oxide	~ 200	310	16%	6%
others [8]	fluorocarbons	45 – 1,700	140– 11,700	effectively all	14%
Note that greenhouse gases with longer lifetimes accumulate more GWP with time.

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 greenhouse gas?

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:

First each GHG (greenhouse gas) is considered separately; that is, gases are theoretically removed and the amount of heat that would remain trapped is estimated.
Here is a sample table quoted from the above link:

Species removed % trapped radiation remaining

All
0

H₂O CO₂ O₃ 50

H₂O 64

Clouds 86

CO₂ 88

O₃ 97

None 100

Data from Rev. Geophys. & Space Sci. 16 (1978) 465"

H₂O = water; CO₂ = carbon dioxide; O₃ = ozone

As you will notice, adding the separate gases together gives well over 100%. This is because some different gases trap some similar parts of the radiative spectrum (see panel of graphs showing the main gaseous components of the atmosphere at the greenhouse effect).

Now GHGs are regarded as ‘forcing’; that is, put more of them into the atmosphere and they increase the amount of heat trapped. You can find more on this at greenhouse effects, with sample tables.
A general estimate is that, without any greenhouse gases, the temperature of the Earth would be 33°C less.
Now a critical question in GHGs is, how long do they stay in the atmosphere?
a) Water vapour is not regarded as a critical forcing GHG because it spends on average far less time in the atmosphere.
b) Water vapour is also regarded as passive. In other words, it (rapidly) adjusts to the conditions in the atmosphere by feedback (see note 5a).
CO₂, once increased in the atmosphere, remains there for large numbers of years. In the present, typical mixture of gases comprising the atmosphere, CO₂ is estimated to be responsible for maybe 12% (100 - 88 from the table above) of the trapping greenhouse effect.
Since industrialisation, the proportion of atmospheric CO₂ is estimated to have increased from about 260 parts per million [ppm] to 360 ppm, and is currently increasing by another net 2 parts a year. For more, see atmospheric carbon.
Given no. 6, doubling atmospheric CO₂ would raise temperatures by 12% of current ‘forced’ levels. That is 12% of the 33°C from no. 3. Thus, 12% more would add nearly four degrees. This would cause further feedback forcing as water vapour came into a new equilibrium.
At 2ppm a year, it would take another 180 years to double the atmospheric load, if other things remained constant (other things probably will not remain constant because of sink issues).
Whatever the forcing in the atmosphere at large, the water vapour will just reach a new equilibrium. However, this new equilibrium will increase the atmospheric water vapour and that will add to GHG heating effects, tripling or quadrupling the CO₂ effect. (This process matters, of course, but annoying as the rising temperature is, it does not of itself produce a runaway effect on earth.)