The assessment by the Intergovernmental Panel on Climate change (IPCC) has provided a detailed and authoritative analysis of what we do know and what we still are uncertain about regarding the ongoing change of the global climate . The global mean temperature has increased by 0.6±0.2 °C during the 20th century , which can not be explained unless the contributions due to human emissions are included . A large majority of the scientific community therefore accepts the notion that a human induced climate change is on the way. Some still maintain an apposite view, but their scientific arguments are generally inconclusive. There is , however, still a significant uncertainly about the sensitivity of the climate system to the disturbances that human activities on earth bring about, nor are we able to spell out in more detail what the characteristics of the change might be, how quickly and where. This is particularly true of the potential regional Climate Change. Similarly, the impacts of a forthcoming climate change are also uncertain. It is of course most essential to analyse these uncertainties more carefully. But there are reasons that justify early actions. The main theme of this paper is to bring home the message that: even if the climate change issue is fraught with uncertainty, a number of quite firm conclusions can be drawn. These should serve as a basis for action. Uncertainties should of course be fully recognized, but must not be the main message. The final judgment about the urgency remains a political issue and will necessarily, to some extent, be subjective.