La nature d’une nouvelle entreprise

Il est tellement facile de faire de l’esbroufe quand on ne veut pas accepter une évidence qui devient de plus en plus incontournable. Il suffit de s’armer de quelques données anecdotiques, de sortir une étude scientifique de sa manche et d’épater la galerie en faisant de la rhétorique (ça vous rappelle «l’affaire Mailloux»?).

David Suzuki attire cette semaine notre attention vers un dossier publié par le magazine américain New Scientist intitulé Climate change: A guide for the perplexed. On y présente 26 mythes souvent donnés pour vérité par les sceptiques pour soutenir leur thèse selon laquelle le réchauffement climatique n’est qu’une invention ou encore que l’humain n’y est pour rien. Chaque mythe est démonté habilement et de nombreux liens vers des sources externes sont donnés pour que l’on puisse pousser plus loin notre réflexion.

C’est vraiment bien fait et intéressant et ça donne de bons arguments pour alimenter le dialogue! J’ai traduit l’énoncé des mythes et collé le paragraphe d’introduction de la page consacrée à chacun. Vous n’avez qu’à cliquer sur les liens pour accéder à toutes les infos. Le dossier complet est ici: Climate change: A guide for the perplexed.

Les émissions de CO₂ causées par l’humain sont trop faibles pour avoir une influence sur le climat

Ice cores show that carbon dioxide levels in the atmosphere have remained between 180 and 300 parts per million for the past half-a-million years. In recent centuries, however, CO₂ levels have risen sharply, to at least 380 ppm. So what’s going on? It is true that human emissions of CO₂ are small compared with natural sources. But the fact that CO₂ levels have remained steady until very recently shows that natural emissions are usually balanced by natural absorptions. Now slightly more CO₂ must be entering the atmosphere than is being soaked up by carbon « sinks ».

Nous ne pouvons rien faire contre le réchauffement climatique

It is certainly too late to stop all climate change. It is already under way, much in line with model predictions. And there are dangerous time lags. There are already several decades of warming in the pipeline. The lags in organising effective initiatives to reduce greenhouse gas emissions are also long. But climate change is not an on-off switch. It is a continuing process. The sooner we stabilise atmospheric concentrations of greenhouse gases, the sooner we can reduce our impact on the climate and minimise the risk of reaching tipping points that will make preventing further warming even harder.

Il a été prouvé que le graphique du «bâton de hockey» n’est pas juste

The « hockey stick » graph was the result of the first comprehensive attempt to work out the average northern hemisphere temperature over the past 1000 years, based on numerous indicators of past temperatures, such as tree rings. It shows temperatures holding fairly steady until the last part of the 20^th century and then suddenly shooting up.

Nous ne pouvons pas prédire les systèmes chaotiques

You cannot predict the exact path a ball will take as it bounces through a pinball machine. But you can predict that the average score will change if the entire machine is tilted.

Nous ne pouvons pas nous fier aux modèles informatiques pour prédire l’évolution du climat

Even though the climate is chaotic to some extent, it can be predicted long in advance. Climate is average weather, and it can vary unpredictably only within the limits set by major influences like the Sun and levels of greenhouse gases in the atmosphere. We might not be able to say whether it will rain at noon in a week’s time, but we can be confident that the summers will be hotter than winters for as long as the Earth’s axis remains tilted.

On avait prédit un refroidissement climatique dans les années 1970

Indeed they did. At least, a handful of scientific papers discussed the possibility of a new ice age at some point in the future, leading to some pretty sensational media coverage.

Dans le passé, ça a déjà été beaucoup plus chaud… alors pourquoi s’en faire avec le réchauffement actuel?

First of all, it is worth bearing in mind that any data on global temperatures before about 150 years ago is an estimate, a reconstruction based on second-hand evidence such as ice cores and isotopic ratios. The evidence becomes sparser the further back we look, and its interpretation often involves a set of assumptions. In other words, a fair amount of guesswork.

Je vis dans une région froide… le réchauffement ne peut que m’être bénéfique

How climate warming will affect you? It depends on where you live, how long you will live, what you do for a living and for fun – and whether you care about the future of your children or humanity in general.

C’est le Soleil qui est responsable du réchauffement, pas les humains

Switch off the Sun and Earth would become a very chilly place. No one denies our star’s central role in determining how warm our planet is. The issue today is how much solar changes have contributed to the recent warming, and what that tells us about future climate.

C’est la faute aux rayons cosmiques

The variation in the total amount of energy reaching Earth from the Sun is one of the main factors determining our planet’s climate.

Le CO₂ n’est pas le gaz qui a le plus d’effets sur le réchauffement

Is water a far more important a greenhouse gas than carbon dioxide, as some claim? It is not surprising that there is a lot of confusion about this – the answer is far from simple.

La basse atmosphère ne se réchauffe pas, elle se refroidit

Increasing levels of greenhouse gases should warm the Earth’s surface and the lower atmosphere, and cool the upper layer. So is this happening as the theory and models predict?

L’Antartique se refroidit, ce qui prouve que le réchauffement climatique n’a pas lieu

There is much uncertainty over exactly how Antarctica’s climate is changing. There are few weather stations, most are on the edge rather than in the interior of the continent and records go back just a few decades.

Les océans se refroidissent

One study in 2006 suggested that the upper layers of the ocean had cooled between 2003 and 2005. The apparent cooling was very slight – just 0.02°C – but needless to say, this should not be happening if the planet is getting warmer (see Cooling oceans buck global trend).

The study was based on measurements taken by a worldwide array of floats (the Argo Network) that monitor the upper 2 kilometres of the ocean. The finding was surprising because other studies have concluded that the oceans are warming very much as predicted.

Le refroidissement qui a été observé après 1940 prouve que le CO₂ ne cause pas de réchauffement

After rising rapidly during the first part of the 20th century, global average temperatures did cool by about 0.2°C after 1940 and remained low until 1970, after which they began to climb rapidly again.

The mid-century cooling appears to have been largely due to a high concentration of sulphate aerosols in the atmosphere, emitted by industrial activities and volcanic eruptions.

À l’époque médiévale, c’était encore plus chaud: il y avait des vignobles en Angleterre

English wine production is once again thriving and the extent of the country’s vineyards probably surpasses that in the so-called Medieval Warm Period. So if you think vineyards are an accurate indicator of temperature, this suggests it is warmer now than it was then.

Nous ne faisons que sortir du Petit âge de glace… c’est pourquoi ça se réchauffe

Some climate sceptics argue that the warming we are now experiencing is simply due to the planet recovering from the Little Ice Age, a period of regionally cold conditions between roughly AD 1350 and 1850. But the key question is why it was colder during the Little Ice Age. And why didn’t the climate remain that way, or even get colder still?

Le réchauffement va causer une glaciation en Europe

While the rest of Earth swelters, might Europe and parts of North America freeze? This scenario was always unlikely, and the latest findings largely rule it out.

L’étude des couches de glace montre que le CO₂ augmente le délai entre les épisodes de réchauffement, ce qui montre que ce gaz n’est pas responsable du réchauffement climatique

Ice cores from Antarctica show that at the end of recent ice ages, the concentration of carbon dioxide in the atmosphere usually started to rise only after temperatures had begun to climb. There is uncertainty about the timings, partly because the air trapped in the cores is younger than the ice, but it appears the lags might sometimes have been 800 years or more.

Les couches de glace montrent que le CO₂ diminue quand la température s’élève

How should past CO₂ levels compare with past temperatures? If there is no relation between CO₂ and temperature, there should be no correlation at all. If CO₂ is the only factor determining temperature, there should be a very close correlation.

Mars et Pluton se réchauffent elles aussi

There have been claims that warming on Mars and Pluto are proof that the recent warming on Earth is caused by an increase in solar activity, and not by greenhouses gases. But we can say with certainty that, even if Mars, Pluto or any other planets have warmed in recent years, it is not due to changes in solar activity.

De nombreux scientifiques réputés remettent en cause le réchauffement climatique

Climate change sceptics sometimes claim that many leading scientists question climate change. Well, it all depends on what you mean by « many » and « leading ». For instance, in April 2006, 60 « leading scientists » signed a letter urging Canada’s new prime minister to review his country’s commitment to the Kyoto protocol.

This appears to be the biggest recent list of sceptics. Yet many, if not most, of the 60 signatories are not actively engaged in studying climate change: some are not scientists at all and at least 15 are retired.

Tout ça n’est qu’une conspiration

Conspiracy (noun): a secret plan by a group to do something unlawful or harmful.

If you believe that tens of thousands of scientists are colluding in a massive conspiracy, nothing anyone can say is likely to dissuade you. But there are less extreme versions of this argument.

L’ouragan Katrina a été causé par le réchauffement climatique

The chaotic nature of weather makes it impossible to prove that any single event such as Hurricane Katrina is due to global warming. It is also impossible to prove that global warming did not play a part, so debates about the causes of individual events are futile.

Des niveaux de CO₂ plus élevés vont stimuler la croissance des végétaux et augmenter la production alimentaire

According to some accounts, the rise in carbon dioxide will usher in a new golden age where food production will be higher than ever before and most plants and animals will thrive as never before. If it sounds too good to be true, that’s because it is.

Il y a de plus en plus d’ours polaires

Polar bears have become the poster children of global warming. The bears spend most or all of the year living and hunting on sea ice, and the accelerating shrinking of this ice appears to pose a serious threat. The issue has even become politically sensitive.

Yet recently there have been claims that polar bear populations are increasing. So what’s going on? There are thought to be between 20,000 and 25,000 polar bears in 19 population groups around the Arctic. While polar bear numbers are increasing in two of these populations, two others are definitely in decline. We don’t really know how the rest of the populations are faring, so the truth is that no one can say for sure how overall numbers are changing.

Vous en voulez plus? Vous n’avez qu’à visiter How to Talk to a Climate Skeptic, une compilation préparée par le magazine Grist.