Climate is a long term average of weather over a period of at least 10 years. Climate change, also known as global warming is the heating of the earth by greenhouse gases. Green house gases mainly consist of methane, carbon dioxide, nitrous oxide and fluorinated gases; these gases trap heat within the surface-troposphere system and cause global warming. Climate model simulation shows that the climate change that we are facing now is due to human activities. The increment in world temperature since the starting of the industrial revolution is due to high carbon dioxide emission.

The International Panel on Climate Change (IPCC) will come out with a synthesis report every seven years and in the most recent AR4 report, it states that temperatures and sea levels will rise even after achieving stabilization of carbon dioxide in the atmosphere. A total of 24 different climate models are used for simulation and they all produced climate models that differ slightly from one another. These models are called global climate models (GCM) on a large scale and regional climate models (RCM) on a small scale. Although the climate of Singapore is modelled using RCM due to its small land area, some of the information is taken from the GCM. The results taken from the RCM can be used for hydrological impact studies such as flooding, soil erosion and temperature rise. Apart from GCM and RCM, there is another model called the weather research and forecast model (WRF). Unlike RCM, this model has to be big enough to observe the full impact. The WRF model for Singapore has to include Vietnam since the monsoon winds blowing from there has a huge impact on Singapore.