Climate Change in the Future
Observations of our past and current climate are essential for validation of the climate models we use to project future climate, and critical in our understanding of climate variability and drivers of climate change.
One of the key challenges of climate change science is determining which changes are due to naturally occurring climate variability and which ones are as a result of human activity.
To make this distinction, scientists undertake detection and attribution studies.
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Detection demonstrates that the climate has changed in a statistically significant way, but doesn't offer any reasons for the change. Attribution establishes the most likely cause of the detected change.
Detection and attribution studies of Australian climate indicate that:
- Warming of climate is unequivocal.
- The widespread warming is very likely to be due to increased greenhouse gas concentrations in the atmosphere.
- A drop in rainfall in south-west Western Australia is likely due to a combination of increased greenhouse gas concentrations, natural climate variability, and land use change.
- The increased summer rainfall in north-west Australia may be due to increased aerosol particles in the atmosphere resulting from human activity, especially in Asia.
- There is growing evidence that lower rainfall and reduced runoff in south-east of Australia is linked to global warmng and cannot be explained by natural variation alone.
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Temperature in Australia
Australia has experienced warmer–than–average mean annual temperatures for 17 of the 19 years from 1990 to 2008.
The mean annual temperature across Australia for 2008 was 0.41°C above the 1961–1990 average, making 2008 our 14th warmest year on record.
Australia's mean temperature for 2008 was slightly lower than the previous six years, partly due to a La Niña event that developed in late 2007 and continued into early 2008.
Over the last century, Australia has experienced an average warming trend of about 0.9°C.
- Globally 13 of the 14 warmest years on record occurred between 1995 and 2008.
- The World Meteorological Organisation has indicated that 2008 global mean temperatures were about 0.31°C above the 19617ndash;1990 average, making 2008 the world’s tenth warmest year on record.
- It is now 23 years since the world has experienced a year cooler than the 1961–90 average.
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.
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.
What is happening to snow cover in Australia? Observations show a decline in snow depth in Australia's alpine region over the last 50 years, although there is a great deal of annual variability.
Observed snow cover trends
- Warming trends are slightly greater at higher elevations.
- Over the past 50 years there has been a small increase in alpine precipitation in New South Wales, and a small decrease in Victoria.
- Some alpine sites have shown a weak decline in maximum snow depth over the period 1957 to 2002. Close analysis at one site indicates a 10 per cent decrease in snow depth since 1962.
- Some alpine sites have shown a moderate decline in mid-late season snow depths (August to September). Close analysis at one site indicates a 40 per cent decrease in spring snow depth since 1962.
The figure above shows time series of maximum snow depth (broken line) and snow depth at first observation in October (solid line) at Spencers Creek in New South Wales. Linear trends indicated with thick lines.
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© 2018 Dionis Kuliev