Temperatures are rising
Measurements of the land and ocean temperatures across the world show an average increase of 0.74 Degrees Celsius over the past 100 years. Larger temperature increases have occurred in places close to the North and South Poles than places near to the equator.
Sea levels are rising
Other indications of higher temperatures have also been observed and measured, including rising sea levels (when sea water heats up, it expands, raising the sea level), the shrinking of glaciers, the shrinking of sea ice at the North Pole, the shrinking of snow coverage in mountains (including the Australian Alps). The change in migration of birds and the shifts towards the poles or to higher altitudes of plants and animals which require cooler conditions, are also indications of warming of the globe.
More often and heavier storms
In most parts of the world there have been more frequent heavy rainfall events, while cyclones and hurricanes have been more intense more often than in recent history. This could happen, or already be happening, in Sydney, but any change in this cannot be shown conclusively in rainfall data at this time.
Changes in average rainfall
Some areas across the world now receive more rainfall over the year (such as parts of the Americas, northern Europe, parts of Asia and north-west Australia) while some areas have become dryer (such as parts of Africa, the Mediterranean, parts of Asia and eastern and south-western Australia).
What about Sydney?
The Sydney region has experienced temperature increases of between 0.5 Deg C to 0.7 Deg C over the past 50 years. Over this period, rainfall in the winter has on average decreased, while there is evidence that rainfall in the summer has increased. These changes are anticipated to continue over the coming 50 years or more. Recent research by the CSIRO has found that there has been fewer storms in southern Australia during the Autumn and Winter resulting in reductions in rainfall of 10% since 1950, during this time of the year. Severe weather events and particularly fire hazardous days will be more frequent in and around Sydney and the Blue Mountains.
Sydney and its Water Supply
Most of Sydney's water comes from dams on rivers inland from the city, particularly the Warragamba and Shoalhaven rivers. The catchment areas for these rivers are expected to experience lower rainfall overall, and higher evaporation and so providing less water for Sydney. In contrast, coastal areas are likely to receive higher rainfall. Details of these expected changes can be found on the Water for Life Understanding Climate Change webpage. More detail can be found in the Summary of Climate Change Impacts on Sydney from the Office of Environment and Heritage.
These changes suggest that, as Sydney's population increases, it would be a good idea for the city to make more use of rainfall that falls on the city itself, rather than depend more on damming inland rivers. (see the Water Sensitive Cities page of this site).