Sea level
Global sea-levels rose 17 cm over the past century.
From 1993 to 2003 global sea level rose by about 3.1 mm a year, compared to 1.8 mm a year when averaged from 1961 to 2003.
Observed sea level is currently tracking near the upper limit of the IPCC projections from 1990 when the projections were first available.
Over half of the observed sea-level rise is due to thermal expansion of the oceans.
Global Mean Sea Level (GMSL): 1870 to 2007
Source: CSIRO, Sea Level Rise—Understanding the past—Improving projections for the future
What is happening to sea levels
The largest source of sea level rise is expansion of the oceans as they warm as a result of climate change. Sea level may also be affected by:
- the melting of glaciers and ice sheets
- variability due to natural cycles over seasonal, inter-annual and decadal time scales (for example, El Niño events)
- regional differences in weather patterns and ocean currents.
Sea level around Australia is measured by a network of coastal and island tide gauges. Australia's oldest sea level records, from Port Arthur, Fremantle and Sydney, confirm rising sea level around Australia.
The polar regions
A recent Antarctic study has found that significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, with warming exceeding 0.1ºC per decade over the past 50 years.
Arctic sea ice reached its minimum extent for the year on 12 September 2009. At 5.10 million square kilometres it is the third lowest extent since the start of satellite measurements in 1979. While this year's minimum is above the record and near-record minimums of the last two years, it further reinforces the strong negative trend in summertime ice extent observed over the past 30 years.
Estimates of the mass balance of the Greenland ice sheet (net loss or gain of ice during a year) show that Greenland has gone from being neutral (no net loss or gain of ice) in 1990 to losing 200–250 km3 (cubic kilometres) per year by 2005.
Recent studies suggest that overall the Antarctic ice sheet is losing mass with slight gains in East Antarctica being outweighed but losses in West Antarctica.
For more information see:
Artic sea: minimum extent of ice in 1982
Artic sea: minimum extent of ice in 2008