1. Climate change: a problem with very specific time scales Hervé Le Treut
Laboratoire de Météorologie Dynamique (CNRS/ Ecole Normale Supérieure /Ecole Polytechnique/Université Paris 6)
Institut Pierre Simon Laplace
Académie des Sciences
LMD

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

3. increased sharply after 1950
The perturbation has
increased sharply after 1950
1950
1900
Energy use: oil, coal and
natural gas account for most of
the increase

4. The consequences have been anticipated by the scientists
on the basis of physical models (results of IPCC 1990
and IPCC 1995, compared to subsequent measurements)

5. They have been detected only recently ….

6. They will have lasting consequences, ….

7. Even at a very long time scale ….
Zero-emissions after 2100:
Effect on temperature and sea-level rise

8. Adaptation to climate impacts: the necessary interactions between decision making and scientific assessment Hervé Le Treut
Laboratoire de Météorologie Dynamique (CNRS/ Ecole Normale Supérieure /Ecole Polytechnique/Université Paris 6)
Institut Pierre Simon Laplace
Académie des Sciences
LMD

9. Assessing the impacts of climate change
is 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

10. Assessing current evolutions provides a necessary insight
into future evolutions. The example of sea-level rise.
Satellite
measurements
Space-borne
instruments
Observed rise:
3.3 mm/year since 1993
In situ measurements
1.8 mm/an
1993
2006
The rise is not evenly distributed!
Yellow/red
blue
A. Cazenave (LEGOS/ Toulouse)

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