Climate Science Summary of Latest Developments A summary prepared by AGL – based upon IPCC and CSIRO research For further information: Tim Nelson Head of Economic Policy and Sustainability [email_address]
The Greenhouse Effect – A Detailed Understanding
Scientists are still perfecting their understanding of the world’s climate
We know the two main influences of our planet’s temperature
distance from sun
composition of atmosphere
‘ Radiative forcing’ is the change in the balance between solar radiation (heat and light) coming into the atmosphere and solar radiation going out
The greenhouse effect refers to the ‘radiative forcing’ properties of the atmosphere
greenhouse gases generally trap heat that is reflected off the Earth’s surface and trap it
other gases (e.g. aerosols) and substances such as volcanic ash reflect heat before it enters the Earth’s atmosphere
There is a clear relationship between the concentration of greenhouse gases in the atmosphere and the average global temperature
Correlation between Carbon Dioxide and Temperature
Greenhouse effect is natural: it is what allows Earth to be habitable. It is the impact of humans on the greenhouse effect that is debated at present
Global concentrations of greenhouse gases have increased markedly over the past century as a result of human activities. Concentrations now far exceed pre-industrial values
The carbon dioxide concentration in 2009 of 386 parts per million (ppm) is much higher than the natural range of 170 to 300 ppm that has existed in the atmosphere for at least the past 800,000 years and possibly the past 20 million years
CO 2 emissions from the burning of fossil fuels increased by two per cent from 2007 to 2008, by 29 per cent between 2008 and 2000, and by 41 per cent between 2008 and 1990 - the reference year of the Kyoto Protocol
The improved understanding of cooling and warming influences on climate has led scientists to conclude with very high confidence (9 out of 10 chance) that the global effect of human activities since 1750 has been one of warming, with a radiative forcing of + 1.6 W m-2.
Variable Current Radiative Forcing Other Information Carbon dioxide, methane and nitrous oxide + 2.30 W m -2 (+2.07 to +2.53) Rate of increase unprecedented in at least 10,000 years Aerosols - 0.5 W m -2 (-0.9 to –0.1) direct and –0.7 (-1.8 to –0.3) indirect Aerosols also influence cloud lifetime and precipitation Tropospheric ozone (i.e. nitrous oxide etc) +0.35 Wm -2 (+0.25 to +0.65) Halocarbons +0.34 Wm -2 (+0.31 to +0.37) Solar irradiance +0.12 Wm -2 (+0.06 to +0.30)
The scientific evidence points to positive radiative forcing as a result of human activities and natural phenomenon
This positive radiative forcing is supported by emerging evidence of actual observed changes to the climate
The linear trend increase in global average temperature is 0.740C (0.56 to 0.92)
The linear warming trend for the last 50 years (0.130C per decade) is nearly twice that for the last 50 years
Since 1960 the mean temperature in Australia has increased by about 0.7 °C .
Average atmospheric water vapour content has increased, mountain glaciers and snow cover have declined in both hemispheres
During 1993 to 2009 sea level rise has been 1.5 to 3mm per year in the south and east of Australia and 7 to 10mm per year in the north and west
Observed Changes in Australia Trend in mean temperature 1960-2009 (ºC/decade) Source: BOM-CSIRO
Observed Changes in Australia Trend in annual rainfall 1960-2009 (mm per decade) Source: BOM-CSIRO
Link between Greenhouse Gases and Climate Change
Most of the observed increase in globally averaged temperatures since the mid 20th century is “very likely” (greater than 9 in 10 chance) due to the observed increase in anthropogenic greenhouse gas concentrations
Alternatively, it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing
Climate scientists believe that any increase in global temperature of 20C above pre-industrial levels is ‘dangerous’
e.g. unstoppable loss of ice cover
Based upon radiative forcing properties of greenhouse gases, a level of between 450 and 550 parts per million of carbon dioxide is necessary to prevent this ‘dangerous’ level being reached
Australian average temperatures are projected to rise by 0.6 to 1.5 ºC by 2030. If GHG emissions continue at current levels, warming is projected to be in the range of 2.2 to 5.0 ºC by 2070.
Warming is projected to be lower near the coast and in Tasmania and higher in central and north-western Australia.
These changes will be felt through an increase in the number of hot days.
Much of Australia will be drier in coming decades
In Australia compared to the period 1981-2000, decreases in rainfall are likely in the decades to come in southern areas of Australia during winter, in southern and eastern areas during spring, and in south-west Western Australia during autumn.
An increase in the number of dry days is expected across the country, but it is likely that there will be an increase in intense rainfall events in many areas.