Global Warming and Associated Changes in the Hydrological Cycle

Abstract

The issue of what the modern world call ‘global warming’ is the climate change primarily due to carbon dioxide released by burning of fossil fuel. Carbon dioxide has a capability to absorb and emit infra-red radiation, and thus acts as a forcing to the climate system. It is expected that climate will warm responding to the forcing. The temperature response will be delayed by several decades because of the heat capacity of the upper ocean, and the sea-level response will be delayed by a millennia because of the response times of the whole ocean and the continental ice sheets. As the climate warms, both precipitation and evaporation will increase in the global average sense, but the increase is not so strong as the increase of saturation specific humidity. On the other hand, local and short-term extreme values of precipitation rate will surely increase. Distribution of precipitation will be more heterogeneous. Paleoclimatological evidence suggests that there are possibilities of rapid climate changes which are not well represented by current numerical climate models used in projection experiments. We should not deny the possibilities of such ‘surprises’, but we are very uncertain about their probability. It would be wise approach to primarily prepare for the climate responses as projected by an ensemble of current state-of-art simulation models, and to secondarily prepare for various uncertain events which include climate ‘surprises’.