Last week saw a draft of the IPCC's upcoming report on the
science of climate change leaked onto the internet. Although it is
not the final version, some
news outlets have reported the contents of the
draft, which provides indicators of how the science of climate
change has changed and developed since the last IPCC report was
published in 2007.
Every five or six years, the Intergovernmental Panel on Climate
Change (IPCC) produces an
in-depth assessment of the state of research in all areas of
climate science, from precipitation patterns to polar ice.
The next one, known as the Fifth Assessment Report (AR5),
is due to be
released next year. But a blogger
leaked an early version online on Friday. So what do the
main differences appear to be between this report and the last
Human vs natural causes
According to the new report, there is now "incontrovertible
evidence" that atmospheric concentrations of greenhouse gases have
increased in the last 200 years, causing the average temperature of
earth's atmosphere and oceans to rise.
So much evidence now exists that the draft says scientists are
"virtually certain" human activity is the main driver of climate
change , which means they are at least 99 per cent sure. In AR4,
the figure was lower -
90 per cent - so scientific certainty has increased.
There is "very high confidence" - which means that there is lots
of supporting evidence - that natural forcing affects the climate
much less than human activity. Solar activity has had a cooling
effect since 1980, the draft report suggests. (Bottom blue bar,
below.) Compare this to the total warming effect from human
activity, shown by the orange criss-crossed bar.