What is Global Warming?
Globally, 11 of the 12 years between 1995 and 2006 were the warmest in the history of global surface temperature records.
In Australia the average temperature has risen by around 0.9ºC since 1950.
The Fourth Assessment Report of the UN's Intergovernmental Panel on Climate Change (IPCC) released in 2007, projects global temperature rises by the end of the century of between 1.1C and 6.4C.
So what is the science behind global warming?
The natural greenhouse effect
Our atmosphere naturally allows the Sun's infra-red radiation to reach the Earth's surface and warm it. The radiation bounces off the Earth's surface into the atmosphere where it is trapped by carbon dioxide, water vapour, nitrous oxide, methane and other gases (collectively known as "greenhouse gases") that are naturally present there. The trapped infra-red radiation makes the lower atmosphere and the Earth's surface warmer than it otherwise would be.
In short, the naturally-occurring greenhouse gases create a blanket-like effect, which maintains an average temperature on the Earth's surface of about 15C.
Natural temperature variations
Throughout history, our planet has experienced cold and warm periods naturally. These are due to variations in the Earth's orbit around the Sun, which affects the amount of sunlight reaching the Earth's surface.
The human-induced greenhouse effect and global warming
For the past 200 years humans have been polluting the Earth's atmosphere with carbon dioxide (CO2) and other greenhouse gases. This traps more of the Sun's infra-red radiation in the Earth's atmosphere, warming the planet.
Rising temperatures and carbon dioxide
As indicated in this diagram, global temperatures have risen significantly in a short time. Scientists attribute this to significant recent increases in the amount of carbon dioxide in the atmosphere.
2000 year temperature compairson
© Global Warming Art
As demonstrated in the diagram below, carbon dioxide concentrations in the atmosphere are closely related to temperature fluctuations. Average temperature increases correspond with an increase in carbon dioxide concentrations.
Vostok ice core petit
© NOAA Satellite and Information Service
The problem now is that carbon dioxide levels in the atmosphere are higher than they have been in the last 650,000 years
The most recent and authoritative assessment of climate change undertaken by the world's scientists in the past five years has concluded that most of the recent warming is due to greenhouse gas pollution resulting from human activities.
