Doc Brown's Chemistry Clinic

Global Warming and CO₂ emissions

The Greenhouse Effect and Climate Change

GCSE⁺ notes and possible class discussion points

I've done my best to sift data and ideas but not all websites are to be trusted, and I'm no expert in this field, so there are lots of ? marks on this page! www.cru.uea.ac.uk/ is a particularly good general resource of ideas, facts, theories etc.but is quite technical in places. EMAIL query?comment

Graph 1: The rise in atmospheric carbon dioxide concentration 1850-2005

• Data Source - NOAA/ESRL Global Monitoring Division: http://www.esrl.noaa.gov/gmd/

• Prior to any growth in industries using fossil fuels the baseline carbon dioxide concentration was about 277 ppm 1000 years ago (277  parts per million means 277 CO₂ molecules in a mixture a million air molecules.

• Rose steadily through industrial revolution but as the world economy gets going after the 2nd World War the rise in CO₂ concentration starts to become much more significant.

• Except in recent times, the CO₂ concentration had reached a maximum of 300 ppm over the last 400 000 years.

• It has now risen steadily to nearly 380 ppm by 2005 and is predicted to carry on rising.

Graph 2: The rise in use of fossil fuel use in terms of CO₂ emission 1850-2003

• Data source - Oak Ridge National Laboratory USA:

• This graph parallels the rise in atmospheric CO₂ concentration in general but seems to be far more significant after the 2nd World War.

• The dips usually (all cases?) coincide with periods of world economic recession e.g. the 1930's and the early 1980's when less fuel is burned by the power and manufacturing industries.

• The steady rise in 'extra' carbon dioxide, presumably from increased fossil fuel burning, is cited as evidence for its contribution to global warming irrespective

Graphs 3 and 4: The Mean Global Temperature variation from 1850-2005

• Data source - East Anglia University, Climate Research Unit:

• The data is based on both atmospheric and oceanic temperatures.

• The purple line is the average global temperature of 14^oC for the period 1961-1990 and is used by some research groups as the baseline for calculating the so-called temperature anomalies plotted below. Essentially the temperature anomaly here = mean global temperature(1961-1990) - 14^o. Other research groups use different baselines and different calculation methods, but they all agree that the Earth is warming up.

• My thanks to Mike Salmon of the Climate Research Unit of East Anglia University, England, for taking the trouble to explain temperature anomaly data to me.

• 1998, 2002 to 2006 were the 6 warmest years on record, at least from 1850 anyway, and 11 of the warmest years have occurred in the last 12. This definitely indicates we are in a warm period, though on a short timescale compared to 'geological time'.

• Although the atmospheric CO₂ concentration is rising steadily, as is the quantity of fossil fuels burned, in cannot be said that the average global temperature has been steadily rising. In fact it shows considerable fluctuation. The temperature tended to fall from the 1940's to the mid 60's, so a new ice age was being predicted in the early 1970's. However the consequent trend in rising temperature is now leading to predictions of 'excessive' global warming and its potentially dire consequences.

• I've explained the theory of the 'Greenhouse Effect' or 'Global Warming' on the Oil Notes page!

• Data source East Anglia University, Climate Research Unit:

• The temperature anomaly graph is a good statistical way of showing the trends i.e. a positive (+) value means warmer than a negative (-) value.

• The purple trend line is based on the polynomial function in Excel, it might not be the real statistical truth BUT its independent of human prejudice!

• There was a significant rise from 1900 (or earlier?) until the early 1940's, then there was a small decrease until 1964, but after that the temperature is steadily rising, which is the worrying feature.

• You can see that from 1950 there is on average a steady rise in temperature despite the regular fluctuations and it is this later temperature pattern that leads most scientist to believe that global warming is a significant threat

Further Environmental, social and economic discussion points etc.

A sort of brainstorm bullet points, and not in any particular order yet, and this section is far from finished for 2007, apart from the opening 2007 IPCC statements below!

The Inter-governmental Panel on Climate Change in its most recent report in 2007 stated:

'Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.'

'Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations12. This is an advance since the TAR's conclusion that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations". Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns'

• Some of the first points made are NOT on the GCSE syllabus, but unfortunately, they are very relevant to the current 'heated' debate on what causes the current global warming. Incidentally, there is no dispute (as far as I know?) in the opinion that the Earth is currently warming up.

• Over the past 2 million years the Earth has passed in and out of ice ages. In terms of the paleoclimatological record we are currently in an inter-glacial period. So, will fossil fuel CO₂ induce global warming to override the historical pattern?

• Two of the major obstacles to good predictions to climatology are accuracy of data (improving) and the fact that changes in climate can be due to changes from what happened several or hundreds of years ago, the great 'systems' of the Earth can only change very slowly (we hope?).

• You can miss out the next two bullet points if you want BUT ... ???? The three Milkankovitch Cycles are to do with the input variation of solar radiation onto the Earth's surface and are considered to be major factors affecting the increase/decrease of glaciation of the Earth's surface.

  1. The eccentricity of the Earth's orbit changes over a 100,000 year cycle. The Earth's orbit around the Sun is not perfectly circular, but is slightly elliptical and changes over a 5% range from a narrower to a wider ellipse. This means that the Earth - Sun distance is smaller/greater leading to an increase/decrease in the intensity of solar radiation reaching the Earth.

  2. Currently the Earth's spin axis is 23.5^o with respect to a vertical line to the plane of its path of its elliptical orbit around the Sun and this causes the change in the angle the sunlight hits the Earth's surface, causing changes in the sunlight intensity and length of day which produces the seasons. However this angle changes over a 41,000 year cycle from 21.5^o to 24.5^o so changing the way the solar radiation is distributed over the Earth's surface and so changing weather patterns and their consequences.

  3. The 3rd Milkankovitch factor is the precession of the Earth's spin axis. The spin axis 'wobbles' and precesses around from one side to another over a period of about 23,000 years.

• As consequence of the interaction of the three Milankovitch cycles, it is believed, and backed up by certain data, that the glacial cycles last about 100000 years and the current interglacial ('warmer period') started about 18000 years ago, but within the 'big cycle' there are cycles and sometimes the effects will combine or cancel each other out producing a very complicated pattern of events which can be plotted to some extent from analysis of ancient ice core data. However, the question till begs, 'will increase in fossil fuel burning override the Milankovitch factors'?

• Despite the mention of Sun spot cycles affecting our climate, and despite the fact that it does affect the total solar radiation reaching the Earth, there is no credible scientific evidence yet that it affects our climate significantly if at all?

• On a short term basis, huge volcanic eruptions of ash clouds can produce mini-ice-age effects which last for several years after the event. The distribution of fine ash clouds can directly block out sunlight or cause more cloud formation which reflects sunlight. Either way, global temperatures will fall due to this 'dimming effect' and long term effects may be more than we recognise, but there is no recognisable pattern in the geological record.

• The Earth is about 5^o cooler than it was 20000 years ago, but it was coming out of the last ice age, and warming up in the 'great climate cycle', so this in not unexpected in principle.

• The current prediction from the IPCC report (Inter-Governmental Panel on Climate Change) based on the work of thousands of 'credible' scientists, is for a one degree rise in average global temperature over the next century. It doesn't sound much BUT it involves  an enormous amount of energy which drives the ocean and atmospheric systems. See the IPCC quotes at the start of this section.

• One consequence is rising sea levels due to thermal expansion of the oceans and the melting of the polar ice-caps, but which is the more significant effect?

• How much of the extra CO₂ will be absorbed by the ocean or used in plant photosynthesis? Is there a significant time lag? Will it have any significant effect at all?

• Do the dips in fossil fuel usage e.g. in the 1930's and 1980's correspond with a temperature fall?

• Will small countries such as the UK make any impact on the situation if their 'carbon footprint' is decreased? especially as China is bringing on-stream a large fossil fuelled power station each week?

• Do we have the right in the developed western economy (e.g. in Europe/USA) to expect less developed countries in the East to show restraint in burning fossil fuels as they try to develop

• Wouldn't it be a good idea if the UK reduces fossil fuels for (a) setting an example or (b) other very different reasons e.g. (i) less dependent on gas/oil supplying countries who may be politically unstable and over control the price, (ii) less need for the very controversial nuclear power, (iii) conservation of a valuable chemical resource for non-fuel use e.g. drugs, plastics and other materials. (a) is a moral-philosophical altruistic attitude, (b) is about self-interest, so why not combine the two?

• Business opportunities due to climate change e.g. if the UK becomes warmer there will be more vineyards in southern England. However the 'warming up' is reducing the skiing tourist industry in Scotland and the Northern Pennines as less snow falls and sticks around, though manufacturers of artificial snow equipment are doing well.

• Ecological changes and their consequences e.g. as the temperature warms up, species tend to move and occupy more northern regions. If the winters are not as severe e.g. less frosts, insect species harmful to plants may not be killed in the same numbers increasing their risk of harming crops. South East may become warmer and drier, so water supplies will be affected and it is an area which is predicted to have the largest number of new houses built in the next decade.

• A selection of actions that can be taken to reduce our 'carbon footprint' is listed on the Oil Notes page and I'm sure many more ideas can be added.

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