INTERVIEW

“We have done terribly little compared with the immensity of the problem.”

Jean-Pascal van Ypersele – “The physics of climate has nothing to do with the political agenda…” © Jacky Delorme (UCL)
Jean-Pascal van Ypersele – “The physics of climate has nothing to do with the political agenda…”
© Jacky Delorme (UCL)
Earth’s climate is influenced by variations in the energy radiated by the solar corona – as clearly visible here during an eclipse – as well as Earth’s position in relation to its star. While these parameters vary over vast expanses of time, they are insufficient to explain the sharp rise in temperatures recorded since the industrial revolution. © ESO
Earth’s climate is influenced by variations in the energy radiated by the solar corona – as clearly visible here during an eclipse – as well as Earth’s position in relation to its star. While these parameters vary over vast expanses of time, they are insufficient to explain the sharp rise in temperatures recorded since the industrial revolution.
© ESO

IPCC(1) Vice-Chair Jean-Pascal van Ypersele presents the current status of scientific knowledge of global warming. Not forgetting the sometimes surprising political reading of the facts…

There now seems to be a consensus that the world is warming, but is it certain that human activities are responsible?

The level of confidence in attributing this phenomenon to human activity is very high and increasing by the year. In 1995, the IPCC wrote that “a range of elements suggests that there is a perceptible influence of human activities on climate”. In 2007, the conclusion was that the greater part of the global warming of the past 50 years is “very probably due” to greenhouse gases of human origin, which translates to a probability of above 90 %.

This assurance is based on many arguments. There are certainly the climate models, which have improved greatly. But also the particular form this global warming is taking: a cooling of the upper atmosphere, as greenhouse gases trap part of the heat of the lower atmosphere that is heating up quickly. If the warming were due to increased solar activity, for example, it would be uniform or even more pronounced in the upper atmosphere. Similarly, we are seeing that the poles are heating up more quickly than the tropics and that is again in line with greenhouse gases being the cause.

What are the principal effects to be feared?

The latest IPCC report devotes hundreds of pages to synthesising impacts that range from falling agricultural yields to various health problems. I should like to stress the importance of hydrological changes: the models predict a significant drought problem in a number of densely populated regions, including the Mediterranean Basin where we are already seeing significant water access problems. Another aspect is the melting of the glaciers in the Andes and the Himalayas that act as a reservoir for hundreds of millions of people for whom there is only rain during a few weeks or months of the year. The rest of the year it is the glaciers that feed the rivers and their programmed disappearance is therefore very worrying.

Then there are the rising sea levels. All the European coastlines could be affected by this, but especially low-lying coasts as in the Netherlands, Belgium and Germany. We will see an increased rate of erosion, saltwater invading the groundwater, increased storm damage, etc. Then in the Nile Delta there are 10 million people living less than a metre above sea level. The sea level will almost certainly rise by at least 50 cm, and perhaps a metre. Where will they go?

What about a 2°C temperature rise as the ‘danger threshold’?

The IPCC has never said that the temperature rise should not exceed 2°C or that atmospheric CO2 concentrations should be kept at under 450 ppm (parts per million). Our job – and the nuance is important – is to say that, for a given emission scenario, we expect a certain level of global warming and a given impact as a result. It is for the public authorities to define what impacts are acceptable as that supposes value judgments and these are not the job of scientists. Historically, the figure of 2°C emerged in 1996 at a meeting of the EU Council of Ministers. It was then in a sense validated by the IPCC’s 2001 report that published the famous ‘burning embers’ diagram that synthesised the gravity of impacts for different temperatures. Its colour code ranged from white to red at around 2°C for the majority of the impacts and this too helped fix this figure in people’s minds when it was based on data more than a decade old.

Are you saying that the latest scientific data call into question this threshold?

We looked again in detail at these impacts, at the request of politicians. The authors of the 2007 report, practically the same individuals as in 2001, concluded that the impact thresholds needed to be revised downwardly by around 0.5°C. Their new graph [See article ‘The tools of diagnosis’ in this issue, editor’s note] was not published in the report but subsequently, in 2009, in the US scientific journal PNAS (Proceedings of the National Academy of Sciences). I have explained how it is not for me, as IPCC Vice-Chair, to define this danger threshold. What I can say, on the other hand, is that if the ministers who met 13 years ago to set the threshold of 2°C and 450 ppm were to meet again today to consider the same criteria as before, they would very probably set the danger threshold at 1.5°C and 350 ppm.

What would be the consequences of such a change in the ‘danger threshold’?

For the moment, the IPCC is not answering this question as the most ‘virtuous’ scenario that it has evaluated in terms of emissions generates a temperature rise of between 2°C and 2.4°C. So we are forced to extrapolate to have an idea of the emissions that would enable us to remain below 1.5°C! I believe this shortcoming will be corrected in the next report – but clearly it will mean rendering all the reduction targets even more constraining.

Have politicians listened more attentively to the IPCC since its last report?

There has been a major positive change – and this does not contradict what I have just said – as the 2°C target was adopted recently at the G8 and then at the G20. This is very important, despite the reservations I have expressed regarding this value, because until then there had not been any figure adopted internationally, and that is the worst possible situation! The United Nations Framework Agreement on Climate Change, adopted in 1992 just before the Rio summit, simply stated that greenhouse gas concentrations must be stabilised “at a level that prevents any dangerous anthropic disturbance in the climate system”. So for 17 years we were without any internationally recognised quantified objective. The adoption of a figure constitutes enormous progress as a whole series of figures stem from that one, principally the emission reduction targets.

So the IPCC’s work is therefore slowly being translated into political decisions?

Except for the fact that the readings of our estimations are often… selective. We said that for a temperature rise of between 2°C and 4°C – and not, please note, below 2°C! – and given the scientific uncertainties, global emissions should reach their peak “between 2000 and 2015”. For some this has already been reduced to “in 2015” and I condemn the fact that just a few weeks ago, for the European Council, this had been transformed inexplicably into “before 2020”! This is perhaps because the European ‘climate package’ was drawn up with 2020 as the horizon, but the physics of climate change has nothing to do with a political agenda.

Let me give you another example. The recent G8, when it adopted the 2°C target, translated this as “a 50 % reduction in global emissions” but without giving a reference year, which suggests that we are referring to present emissions. But in its report the IPCC said that global emissions should be cut by 50 % to 85 % compared with the 1990 levels. Since then emissions have increased by around 40 %! To sum up, independently of any consideration of our ability to achieve these targets, the targets currently envisaged at international level fall short of what would be needed to protect populations and ecosystems.

What remains to be done in reducing emissions?

We have done a lot – but it remains terribly little compared with the immensity of the problem. Take the Kyoto Protocol: the aim was to reduce emissions by 5 % in 22 years for the developed countries (between 1990 and 2012) and this target will probably only just be met at best. But what we now need to do in these same countries is reduce emissions by between 80 % and 95 % in 40 years, which would permit a reduction of between 50 % and 85 % for the planet as a whole. And by the end of the century emissions should be zero. This supposes a fundamental review of the way we consume, of the way we produce – not just energy but all goods, of the way we travel, and of the way we live and work… A genuine revolution!

Interview by Yves Sciama

  1. IPCC: International Panel on Climate Change. Jean-Pascal van Ypersele is a physicist, climatologist and professor at the Institute of Astronomy and Geophysics at the Catholic University of Louvain (BE).

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