By Claire

Last week, the CSIRO and Bureau of Meteorology (a.k.a. BOM) released their ‘State of the Climate’ report for 2012. This report compiles the most recent data on the progression of climate change, summarising scientists’ understanding of climate change to date.

Despite the recent cool and wet conditions we have been experiencing on the east coast of Australia during 2011, the report warns us that the underlying warming trend, which is associated with climate change, is continuing. We need to make sure to separate weather and climate when talking about climate change. Climate involves long term trends, which is what we are looking at with climate change.

Will Steffen, the executive director of ANU’s Climate Change Institute put the cool and wet weather into context in a recent interview, ”Last year was something we now consider cool. Yet just a decade ago … this would’ve been the second warmest year for 100 years.”

The report states that the levels of carbon dioxide in the atmosphere have reached 390ppm (parts per million), which is more than at any other time during the last 800 000 years. Current levels of CO2 in the atmosphere are well beyond the degree of warming we have already seen, indicating that even if all carbon emissions were to stop today, we would still experience further warming due to the lags in the Earth’s climate system. 

Summary of the main points of the report:

Temperature

  • Each decade has been warmer than the previous decade since the 1950s.
  • Australian annual-average daily maximum temperatures have increased by 0.75°C since 1910.
  • Australian annual-average daily mean temperatures have increased by 0.9 °C since 1910.
  • Australian annual-average overnight minimum temperatures have warmed by more than 1.1 °C since 1910.
  • 2010 and 2011 were Australia’s coolest years recorded since 2001 due to two consecutive La Niña events

Rainfall

  • Southwest Western Australia has experienced long-term reductions in rainfall during the winter half of the year.
  • There has been a trend over recent decades towards increased spring and summer monsoonal rainfall across Australia’s north, higher than normal rainfall across the centre, and decreased late autumn and winter rainfall across the south.

Oceans

  • 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.
  • 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 in 2010 were the highest on record.
  • Sea-surface temperatures have increased by about 0.8 °C since 1910.

Greenhouse gases

  • Fossil-fuel CO2 emissions increased by more than 3 per cent per year from 2000 to 2010.
  • The concentration of CO2 in the atmosphere in 2011 was 390 parts per million – higher than at any time for the past 800,000 years.
  • The main cause of the observed increase in CO2 concentration in the atmosphere is the combustion of fossil fuels since the industrial revolution.

Understanding global warming

  • Both natural and human influences affected climate over the past 100 years.
  • It is very likely that most of the surface global warming observed since the mid 20th century is due to anthropogenic increases in greenhouse gases.
  • Human activities also have influenced ocean warming, sea-level rise, and temperature extremes.
  • The warming around Australia is consistent with the global pattern and cannot be explained by natural variability alone.
  • There is evidence of changes in extreme temperatures globally.
  • No significant trends in the total numbers of tropical cyclones or in the occurrence of the most intense tropical cyclones have been found in the Australian region

Future changes

  • Australian average temperatures are projected to rise by 1.0 to 5.0 °C by 2070 when compared with the climate of recent decades.
  • An increase in the number of droughts is expected in southern Australia but it also is likely that there will be an increase in intense rainfall events in many areas.
Read the full report here.