• Issue 1
• Politics and Society

[Also in Italian ] Gordon Brown, the British prime minister-in-waiting, and David Cameron, the Tory leader, have something in common - they both want Britain to be the world leader in the fight against climate-change. Whoever the PM, Britain will try to reduce the greenhouse gas emissions by 12.5 per cent by 2012 compared with 1990 levels.

In 2003, the British government wanted to go beyond the Kyoto protocol, cutting the emission of carbon dioxide (CO2) by 20 per cent by 2010, and by 60 percent by 2050.

But, while it seems that there is a consensus between politicians that climate-related problem can be tackled by reducing the amount of emitted CO2, not all the scientists agree on that point. 

You don't need to be a scientist to see the damages human pollution has made to the planet in the last centuries. Petrol, for instance. In addition to CO2, which is not toxic, petrol engines emit toxic substances, and for a better quality of life we should drastically decrease their usage. Shortage of petrol, reflected in higher-than-ever prices, poses a problem on who and how we should use it. Part of today's political instability is due to the scarcity of that energy source.

Regarding CO2 and climate change, it seems that the majority of the media, no matter the political affiliation, are giving misleading information. Some forgotten truths, for example, are that without the greenhouse effect, we could not survive; that CO2 is not a very important greenhouse gas; or that an increase of CO2 in the atmosphere has never overheated the planet. Nor has a decrease cooled it down.

What is the green house effect?

The Earth receives energy from the Sun in the form of light. It warms up and re-emits some energy as radiation. Part of this radiation is absorbed by the atmosphere and does not leave our planet. The energy which remains "trapped" in the atmosphere is the greenhouse effect. Without this, life would be hard on Earth, as temperatures would drop at least 30 degrees. That is perfectly known to anybody who has studied the basics of Earth science.

The greenhouse effect stabilises the temperature of our planet. If the Sun emits more energy, the temperature of the Earth increases, thus more energy escapes through the atmosphere, and after a while a new equilibrium is set. It can also be the other way around: if the greenhouse effect increases, the temperatures go the same way. Until a bit more energy escapes from the atmosphere, and then the equilibrium is set again.

For these two reasons -i.e. changes in Sun energy emission or greenhouse gasses concentration - temperature, on a scale of hundreds of years, can easily have an oscillation of 2-3 degrees. On a bigger time scale temperature has a bigger oscillation, as shown later, and for different reasons.

How does the greenhouse effect work? The gas molecules absorb a small quantity of radiation, and then re-emit it in the opposite direction. Molecules like nitrogen (N2) or oxygen (O2), which are about 98 per cent of our atmosphere, are not good at that. Ozone (O3) is relatively good whereas carbon dioxide is nowhere near as efficient. Water (H2O) is excellent, and is responsible for 70 per cent of the greenhouse effect. With clouds, the greenhouse effect is about 20 per cent higher than without. The greenhouse effect is about 150 Watts per square meter. CO2 global warming effect, according to the IPCC, has increased by 1.52 W in the last 200 years. That accounts for about 1 per cent of the total effect, i.e. 0.3 degrees. 

The problem with water vapour is that it is particularly difficult to model. It acts mainly locally, it changes rapidly, and if condensed (in clouds) increases the solar energy which is reflected in the atmosphere before reaching the Earth, a phenomenon known as the albedo. A cloudy night is warmer after a sunny day because of the greenhouse effect, but a cloudy day is colder than a sunny day.

Image: Creative Common licenced by I. Rooney  

Next part : Carbon Oxide concentration in the atmosphere and Earth temperature