Climate change: a problem with very specific time scales

Hervé Le Treut

LMD

Laboratoire de Météorologie Dynamique (CNRS/ Ecole Normale Supérieure /Ecole Polytechnique/Université Paris 6)

Institut Pierre Simon Laplace

Académie des Sciences

Our planet is confronted to a situation which was never encountered in the history of human civilizations:

The perturbation has increased sharply after 1950

Energy use: oil, coal and natural gas account for most of the increase

19001950

The consequences have been anticipated by the scientistson the basis of physical models (results of IPCC 1990

and IPCC 1995, compared to subsequent measurements)

They have been detected only recently ….

They will have lasting consequences, ….

Even at a very long time scale ….

Zero-emissions after 2100:

Effect on temperature and sea-level rise

Adaptation to climate impacts: the necessary interactions between decision making and

scientific assessment

Hervé Le Treut

LMD

Laboratoire de Météorologie Dynamique (CNRS/ Ecole Normale Supérieure /Ecole Polytechnique/Université Paris 6)

Institut Pierre Simon Laplace

Académie des Sciences

Assessing the impacts of climate changeis a process confronted with many difficulties:

- The predicted amplitude of future climate change lies within a certain uncertainty range

- Potential impacts are very different in nature: heat waves, droughts, cyclone intensification, ocean circulation changes, sea-level rise, modification of ecosystems and loss of biodiversity, health, economic activities

- The climate system is non-linear and may evolve abruptly when certain (unprecisely known) thresholds are reached

- The consequences of climate changes also depend on other anthropogenic

factors: direct modification of the biodiversity, water management, soil use, geopolitical tensions, …

A constant interplay between scientific measurements and decision making is necessary to define and revise continuously an adaptation stategy to climate change

Space-borne instruments

1.8 mm/an

In situ measurements

Observed rise: 3.3 mm/year since 1993

Satellite measurements

The rise is not evenly distributed! Yellow/red blue

1993 2006

Assessing current evolutions provides a necessary insight into future evolutions. The example of sea-level rise.

A. Cazenave (LEGOS/ Toulouse)

Assessing current evolutions provides a necessary complement to modeling approaches. A summary of current physical and biological observations by IPCC Working Group II.