Earth's climate has varied considerably over the course of its history. The geological and palaeoclimatic record bears witness to glacial periods, warmings, prolonged droughts and rapid shifts. This natural variability in no way diminishes the present role of human greenhouse-gas emissions. It is a reminder that a climate system can respond non-linearly to a sustained perturbation.
Contemporary societies developed on the assumption that the conditions observed in the recent past would remain regular enough to guide land-use planning, agriculture, infrastructure and insurance. When averages shift and certain events become more likely or more intense, that dependence comes fully into view.
The myth of climatic stability
Climate archives describe gradual trends, oscillations and regime shifts. The notion of climate itself rests on statistics established over a given period. It helps compare states of the system without promising permanent immobility. To imagine that a single intervention would suffice to restore a fixed normality is to mistake a useful reference for a definitive natural state.
Even with a global target, weather will remain chaotic
Weather will retain its variable and partly unpredictable character whatever the emissions scenario. Limiting warming will make neither storms, nor floods, nor droughts disappear. Targets expressed in degrees serve to contain the evolution of risk at the global scale. They are not a command capable of fixing local conditions.
A change in mean temperature alters the distribution of many phenomena. The consequences then depend on territories, seasons, exposure and the vulnerability of populations. A global average does not directly describe what will be experienced in a valley, a city or a farm.
Dependence on narrow conditions
Energy, food, logistical, financial and urban systems often rest on limited operating ranges. Tightly run supply chains hold little slack. Infrastructure sized from historical data may become inadequate. Urbanisation sometimes increases exposure by concentrating people and assets in already vulnerable areas.
Risk arises from the encounter between a hazard and this material organisation. Reducing emissions acts on the future evolution of the climatic hazard. Adaptation acts on exposure, dependencies and response capacity. The two movements are complementary.
Inhabiting instability
Inhabiting a changing climate calls for keeping margins, diversifying certain resources, maintaining infrastructure and revising standards as observations evolve. Redundancy has a cost, but its absence also has one when several failures combine. A resilience policy must arbitrate between these costs according to the risks specific to each territory.
Conclusion
Knowledge of the climate makes it possible to anticipate part of what is coming without removing uncertainty. Our choices can still limit the extent of warming, reduce exposure and preserve adaptive capacity. The soundness of a society will depend on its ability to act on these three dimensions rather than wait for the return of a climate presumed immobile.
Principal source: IPCC, Synthesis Report of the Sixth Assessment Cycle.