Science
A scientific theory to explain human-caused global warming has been available since 1896, drawing on earlier roots. Since then, scientists from numerous disciplines have pieced together evidence to develop explanatory and predictive models that become more and more robust as research expands.
Policy
The first authoritative milestone in official recognition of the risk of climate change was probably the 1990 First Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) which observed that:
“The potentially serious consequences of climate change on the global environment give sufficient reasons to begin by adopting response strategies that can be justified immediately even in the face of significant uncertainties.”
Not exactly unambiguous, but a flashing amber light. The lights turned to red with IPCC 2 in 1995. In its careful language, delaying mitigatory measures “may leave a nation or the world poorly prepared to deal with adverse changes and may increase the possibility of irreversible or very costly consequences.”
Pressure from governments has moderated the crispness of the IPCC’s scientific consensus and has caused its successive reports to repeatedly err on the side of caution. Its most recent reports leave no room for doubt about the perils awaiting the earth’s life support systems.
The Australian Government (along with the US Government during the Trump administration) has been an outlier in international circles because of political resistance to heeding the scientific evidence.
Explanatory materials
Australian Dr John Cook has developed a website www.skepticalscience.com with comprehensive explanations of the science, the denialist contradictions and responses to denialists’ fabrications. The website has a wealth of material on climate change and global warming. The site is tailored towards a popular audience and is authoritative.