The IPCC Report (Intergovernmental Panel on Climate Change 2007) raises serious concerns about the increase of extreme weather events (storms, rains, snowfalls). Over the past 100 years the average global temperature has risen by around 0.75°C and the sea level increases by 3 millimetres a year. There is a consensus on the impact of this climate change phenomena on the planning and operation of the electric power systems: winds are growing in strength, resulting in a greater frequency of operations interruption (falling trees, avalanches, etc.). Furthermore, due to the increasing incidence of heavy precipitation, lines and substations are often flooded, damaged or destroyed. Repairing the resultant damage is often very time-consuming. And also the temperature of permafrost layers is rising. As a result the bedrock is becoming loose. This in turn increases the risk of landslides, which also damage and destroy lines and substations. There are many cases of extreme weather which have caused enormous damage to electric power systems, e.g. the ice storm in Canada (1998) or the hurricane "Lothar" in Western Europe (1999). Considering the climate change at the planning of electric power systems is therefore highly relevant. In order to plan the power system we need to evaluate the risk of outages due to extreme weather. The vulnerability is assessed, based on historic meteorological data. It results in geographic and seasonal exposure maps. E.g. in Switzerland, alpine regions are more prone to extreme conditions which can vary from one valley to the other. In this paper, the planning methodology uses scenarios to assess the uncertainty related to the vulnerability of the power system under extreme weather conditions. These scenarios are based on weather-related contingencies and reference cases of the Swiss transmission system. The climate change has also to be considered at the operation of electric power systems. At the control centres new operating tools have to be introduced which take into account the impact of the climate change, e.g. an early warning weather system, or a Geographic Information System (GIS) which pinpoints (together with information of protection systems), the location of a damaged line so that the repair staff can be on the spot very quickly, thereby minimising downtime. Furthermore the dispatchers must be trained on how to manage their electric power system during extreme weather conditions. Finally experienced crisis organisations must be established.