Oceans

Key points Global average mean sea level for 2011 was 210 mm above the level in 1880. Global average mean sea level rose faster between 1993 and 2011 than during the 20th century as a whole.

Rising global-average mean sea level

Global average mean sea level for 2011 was 210 mm (± 30 mm) above the level in 1880, the earliest year for which robust estimates of global-average mean sea level are available.

The observed global average mean sea-level rise since 1990 is near the high end of projections from the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report.

 

Rising sea level around Australia

Rates of sea-level rise are not uniform around the globe and vary from year to year. Since 1993, the rates of sea-level rise to the north and northwest of Australia have been 7 to 11 mm per year, two to three times the global average, and rates of sea-level rise on the central east and southern coasts of the continent are mostly similar to the global average. These variations are at least in part a result of natural variability of the climate system.

 

 

Key points The heat content of the world’s oceans has increased during recent decades, increasing the volume of ocean waters and contributing to sea-level rise. Sea surface temperatures around Australia have increased faster than the global average. Sea surface temperatures in the Australian region were very warm during 2010 and 2011, with temperatures in 2010 being the warmest on record.

Ocean heat content

One of the best indicators of changes in the climate system is the amount of heat stored in the oceans. The heat content of the world’s oceans has increased during recent decades and accounts for more than 90 per cent of the total heat accumulated by the land, air and ocean since the 1970s. This warming increases the volume of ocean waters and is a major contribution to sea-level rise. Ocean warming is continuing, especially in the top several hundred metres of the ocean.

Increasing sea surface temperatures

Sea surface temperatures in the Australian region were very warm during 2010 and 2011, with temperatures in 2010 being the warmest on record. Sea surface temperatures averaged over the decades since 1900 have increased for every decade. Sea surface temperature datasets are separate to land temperature datasets, but both terrestrial and ocean surface temperatures have shown very similar warming trends over the last century, confirming that temperatures are rising.

The warm sea surface temperatures in 2010-11 were strongly influenced by La Niña. La Niña events are typically associated with warmer-than-average ocean temperatures in the Australian region. Ocean temperatures around Australia were warmer during 2010-11 than for any previously identified La Niña event, likely due to the influence of the long-term warming trend of the past century.