Global climate change:
from scientific theory to actions

Editorial

François Valérian

 
Global warming and the greenhouse effect
Michel Petit

Understanding and foresight

Global warming: Finding and attributing causes
Serge Planton

The last report made by the Intergovernmental Panel on Climate Change has concluded that the average increase in global temperatures since the mid-20th century mainly comes from rising anthropogenic emissions of greenhouse gases. This conclusion has come out of a slow process of demonstration, which compared observations with simulations of climatic change. Most statistical studies that have detected signs of such a change and attributed them to various sources, natural or human, have strengthened the experts in their conviction. Recent studies conducted in France, while also setting globally warming down to human activities, open paths toward exploring regional effects and toward validating the tools and models used to make projections about the climate.

Projections
Michel Déqué

For twenty years now, scientific reports and studies have provided many a figure and map of possible future trends in our planet’s climate. Among the results obtained from various models, attention is turned toward the statistics and trends detected in French studies that are part of this international effort to simulate the climate for the planet as a whole, for a few regions, for Europe and for France. While bearing in mind that these are not predictions, we can hope that ever more complex simulations will help us better understand how the climatic system reacts.

Taking stock: Fossil fuels
Nathalie Alazard-Toux and Yves Mathieu

Given that fossil fuels now make up 80% of the energy supply for our planet’s 6,5 billion inhabitants, we must tap new reserves. The 21st century is predicted to be a time of transition from heavy dependence on fossil fuels toward a diversification of energy sources and a growing share for replenishable ones. Control will have to be exercised so that this transition will not harm our economies and will be acceptable to everyone. Petroleum, natural gas and coal will still form a major part of our energy supply in the coming decades. The problem in the middle run is not resources as such, even though they are limited, but rather their transformation into reserves that can be worked. Specialists are hesitating between two possibilities.

The consequences for farming
Bernard Seguin

From rapeseed in Scandinavia to grapevines in Great Britain, farming has been flexible, and might soon have to prove that it can adapt to global warming. But where and when? The effects vary depending on the region and crop. A line of demarcation runs between areas in the middle and upper latitudes, which might benefit from moderate warming (1-3° C), and countries in the South, which will probably be losers under these same conditions. The hypothesis of temperatures rising more than 3° C leads to a sharp decline in crop yields of every sort in all regions. The impact would be catastrophic in the South; and agriculture in the North would have to undergo major changes. Let us not lose from sight that other determinants will come into play that might, or might not, turn out to be more significant than a change of climate. But the general trend clearly stands out: whereas temperate zones can expect effects, some positive, others negative, on crop yields, the impact of climatic change will nearly always be negative in the tropics.

Ecological systems and climate change
Henri Décamps

In all environments, on land, in salt- or freshwater, ecological systems are changing in response to global warming. Though moderate till now, the temperature increase over the past thirty years has already left its marks on life on our planet and set off far-reaching reactions. Simulations of global warming for the coming decades bear evidence of even bigger reactions, ecological and, too, social as well as economic. It is urgent to slow down current trends.

The impact of climate change on the water cycle
Hervé Douville, Jean-Claude André and Ghislain de Marsily

The increasing concentration of greenhouse gases in the atmosphere makes global warming inevitable. Simulations of the climate provide us with a good picture of this phenomenon. Although projections for the water cycle are not so clear or certain, we should not conclude that this uncertainty justifies putting off preventive measures. It is highly probable that human populations and societies are much more (and much sooner) sensitive (and vulnerable) to hydrological than to thermal changes of the sort that will be occurring in a near future. For this reason, a major part of the planet’s population — the most underprivileged — will bear the brunt first.

The need for action

 
Global warming and greenhouse gases: Nuclear energy
Bertrand Barré

To limit global warming, a larger proportion of our energy must come from sources that do not emit significant quantities of greenhouse gases. We can count these sources in short order. Besides replenishable sources, there is nuclear energy. Given the 442 nuclear power plants on the planet and the 2.600 billion kWh of electricity produced in 2005, this industry is already contributing significantly to the fight against global warming. It could enlarge its contribution were public reluctance overcome. Given the scale of our energy needs and the threat of global warming, nuclear power has not-to-be-overlooked advantages. It does not solve all problems, but the latter will not be solved without it.

Replenishable energy: How does it help fight against greenhouse gases and global warming ?
Erik Guignard

Since renewable sources of energy do not emit greenhouse gases and are widely spread around the planet, they are — naturally — at the center of all prospective studies for reducing emissions. In particular, they lie at the center of the European Commission’s proposals for Europe in 2020, which were ratified at the meeting of EU heads of states on 7-9 March 2007. The predicted increase in the share of replenishable sources in the French energy supply must go in hand with efforts to control consumption in housing and transportation. Let us not forget: since greenhouse gases, which cause global warming, are a planetary problem, any solution will have to be worldwide. A few thoughts on the prospects for France…

Saving on energy in transportation
Claude Gressier

The fight against global warming is a major challenge for the 21st century. The aim is no longer to save energy “along the margins” but to divide by three or four CO₂ emissions by 2050. The Conseil Général des Ponts et Chaussées undertook, for two years, a futurological study to determine how much of these savings could come from transportation. There are solutions for making economic development compatible with social activities. Some of them call for decisions at the European or even planetary level; others involve the responsibility of national governments and local authorities. These solutions are an obligation for all of us.

How to organize so as to halve CO₂ emissions worldwide ?
Yves Martin

In the coming fifty years, it will not be possible to cut worldwide CO₂ emissions in half at a moderate cost unless all countries join in the effort. The best means would be a tax that would replace other fiscal instruments in national systems. It would simplify international negotiations by limiting the search for an agreement to two factors: the amount of the tax and its rate of increase. Furthermore, it would spare newly developing countries from taking paths that we have had to abandon. In transportation however, other determinants affecting price schedules will have to be used.

The international climate in 2007
Dominique Dron

The scientific evidence is accumulating: the damage due to climatic change is becoming ever more obvious. Tensions related to fossil fuels and resources characterize a world with more than six billion consumers. The status of negotiations about global warming has changed, this marginal environmental topic having become a key issue in North-South relations. We have fewer than ten years to start controlling emissions worldwide, and a scant three years to design and adopt, at the planetary level, a framework justifying this control. Will the gradual crystallization of interests in favor of a worldwide response to global warming enable us to catch up with climate change ?

Controlling emissions and the costs: The conditions for worldwide actions
Cédric Philibert

The Kyoto Protocol, as amended or a new text… we must start preparing for what will happen after 2012. Europe must not fall to the temptation to act alone, a choice with little impact on either total greenhouse gas emissions or current negotiations. The issue is worldwide; and plans for action must bring all partners together, starting with those, ranging from developing countries to the United States, who do not want the protocol to stipulate quantifiable standards for emissions. We must try to imagine solutions that meet their objections: guarantees that setting such objectives will not impair economic development, and assurances that the uncertainty related to costs can be reduced.

To define the state’s role, the diagnosis must not be mistaken !

Henri Prévot

Heat waves and hurricanes, ever more scientific reports, rising oil prices… French public opinion has changed to the point of accepting the idea of reducing greenhouse gas emissions. There is a risk: lest an error in the diagnosis conceal the role that the state should play. Although the price of petroleum has flared, we cannot be sure it will remain at a level high enough for humanity to win the fight against global warming. In its own interests, France should take action without waiting for international or European coordination, whence an essential role for the state. Here are a few proposals for a program that can arouse confidence, but political authorities will have to create the conditions for its widespread acceptance by convincing public opinion that the effort requested is, indeed, justified.

Miscellany

 
Chinese growth and the environment
Paul-Henri Bourrelier and Xiaoming Li

Economic growth, industrialization, an increase in purchasing power for part of the population and an acceleration of urbanization, all this has augmented the pressure and turned China into a major producer of greenhouse gases. Will the country straighten out, adjust its growth and make a “soft landing”? Or will the environmental menace disrupt development? Public authorities will probably impose more effective regulations and improve the efficiency of using resources. The actual risk is indirect, and social: the path taken by China has worsened inequality, since the poorest fraction of the population has not benefitted from growth. To ward off this risk, efficiency has to be improved significantly and fast by adopting a real market economy with emphasis on quality and on saving scarce resources. Everything is interrelated.