Global warming and why it matters

This piece was originally in the ANTAS (Association of North Thames Amenity Societies) newsletter, edited by Merrin Molesworth, and was kindly sent for inclusion in Chiltern News. Comments are invited from readers. Presentation by Penelope Tollitt.

The highlight of this autumn’s ANTAS (Association of North Thames Amenity Societies) meeting was a presentation given by Penelope Tollitt, Spatial Planning Manager of Wycombe District Council. Based on a recent presentation to the Council, this was followed by recommendations for further reading by Penelope’s husband, Michael Tollitt, Chartered Environmentalist, historian and architect.

Although most members of civic societies will be very familiar with the issue of global warming, the presentation was so clear and compelling that we felt that the key arguments should be summarised here.

CO² and Global Warming
The subject has now moved up the political agenda, not least due to Al Gore, former US presidential candidate, with his book and film An Inconvenient Truth. Highly respected think-tanks in the UK, America and Australia say that there are now “just 10 years to save the world”. By then average global temperatures could have risen by 2C, and this could represent “a point of no return”. Seven key questions are often asked:

1 What is global warming?
A time-line of world history shows just how stable climate has been since the end of the last ice age, some 10,000 years ago. The entire history of agriculture has been within this period. The mediaeval climatic ‘optimum’ corresponding to settlements in Greenland, and the ‘little ice age’ with the Frost Fairs on the Thames, (recorded in paintings and writings of the time) represent just minor fluctuations compared to the rate of change we are now seeing.

The mechanism of warming was explained in terms of sunlight passing readily through the atmosphere to warm the surface of the earth. However, the resultant warmth that is reflected back towards space is mainly infra-red radiation, and some of this is trapped by gasses in the atmosphere. Carbon dioxide absorbs in the infra-red, and the more CO² in the atmosphere, the more this warmth is retained; hence the term ‘greenhouse effect’.

2 What is climate change?
Climate change is a reality as shown by Hurricane Katrina, visible from space as a vast vortex of cloud. Such events are likely to become more common, and of greater severity, as the oceans warm. Changing rainfall patterns are already a reality, while predictions of the warming effects being greater towards the poles are confirmed by observed temperature changes and melting ice sheets.

3 How do we know it is happening?
A graph of near-surface temperatures since 1861 provides compelling evidence of a take-off in temperature, initially from the 1920s, but then strongly from the 1980s. When examined by specific locations around the world, the greatest increases are found in the higher latitudes away from the equator, in accordance with prediction. Further confirmation of the changes is provided by a graph of sea levels, showing rapid and consistent rise throughout the 20th century, and by the evidence of retreating glaciers, world wide.

4 How do we know it is related to CO²?
The graphical evidence is striking. A chart of CO² levels in the atmosphere over the last 1000 years shows a remarkably consistent level of around 280ppm (parts per million). The take-off started in the mid-19th century, and dramatically accelerated in the final decades of the 20th century to reach around 380ppm today. But even more remarkable are the data for both CO² levels and inferred temperatures over a much longer period. These cover some 600,000 years and include several of the Pleistocene ice ages and interglacial periods. CO² levels are now much higher than they have ever been over this period, and also there is a very strong correlation between the graphs of temperature and CO² concentrations. Although the CO² levels fluctuated during the ice ages, the present high levels represent uncharted territory, with the most serious implications for further temperature increases.

5 How do we know it is caused by man and is not ‘natural’?
The chart of CO² emissions on a year-by-year basis since 1850 show a steady rise during the Industrial Revolution, through to a much more rapid take-off around 1950. CO² emissions have increased from around 6Gt per annum in 1950 to some 25Gt per annum today, and are still rising fast. (Gt = Giga tonnes or 1 billion tonnes.) CO² emissions from the use of fossil fuels are only part of the story, and amount to just under two-thirds of all greenhouse gas emissions when quoted on a CO² equivalent basis (some gases, particularly methane, have a much more potent greenhouse effect, and relatively small emissions of these are equivalent to a much larger quantity of CO²). Burning fossil fuels, and deforestation and intensive farming are all human activities, and this large-scale release of greenhouse gasses can only be seen as being man-made.

6 What is different to previous natural warmings?
Over the last 600,000 years there has been a series of ice ages interspersed by relatively brief interglacial periods when temperatures were as warm as today, or even warmer. However, CO² levels are so much higher today than during any of the warm interglacial periods, that we are seeing conditions quite unlike anything that has gone before (at least within this timescale). And it is now quite clear that high levels of CO² in the atmosphere are driving up temperatures at an unprecedented speed.

7 What is going to happen?
There will be effects on temperature, rainfall, biodiversity, extreme weather events, social impact and economics. All are inter-related and individual effects cannot be isolated. There is also risk of 'positive feed-back'. For example, as ice-sheets melt, highly reflective ice and snow are replaced by dark rock or ocean. These absorb more of the sun’s warmth, and so contribute increasingly to global warming. The situation could be inherently unstable, with a relatively modest temperature rise initiating events that could lead to much further warming.

Examples of the consequences were given, including the deaths in the Paris heatwave of 2003, the increasingly severe risk of flooding in London, the increasing frequency of forest fires, the rapidly increasing cost (insured and otherwise) of extreme events, loss of species and threats to human populations. The final quote was from Sir David Attenborough in his recent BBC programme: “I am no longer sceptical. Now I have no doubt at all. Climate Change is the major challenge facing the world. People say it will be all right. It won’t.”

Further reading
Following any of these links will open an additional browser window, which you should close in order to return here.
Michael Tollitt’s recommendations for further reading can be found at:
www.antas.org.uk/events

Other links
www.climatecrisis.net
www.ukcip.org.uk
www.metoffice.com/research/

 
“I am no longer sceptical. Now I have no doubt at all. Climate Change is the major challenge facing the world. People say it will be all right. It won’t.”
Sir David Attenborough