Geoscience Reference
In-Depth Information
Though CO
2
is a greenhouse gas, its warming efficacy rapidly diminishes (in
logarithmic fashion) as atmospheric concentrations rise.
Whenbothpositive(e.g.enhancedwatervapour)andnegative(e.g.enhancedlowlevel
cloud) feedback effects, and geological climate records, are taken into consideration, little
likelihood exists that conceivable levels of human emissions will cause dangerous future
warming.
Common ground amongst global warming protagonists
These four contextual scientific matters discussed earlier all point to a lack of alarm
regarding dangerous global warming caused by humanrelated greenhouse gas emissions,
despite which a vigorous public debate about the matter continues. This debate is strongly
antagonistic, belying the fact that a large measure of scientific agreement exists between
the debating protagonists about most of the facts of the matter.
The common scientific ground and the main matters that remain in dispute are
summarised in Table 1.
Table 1: The essence of the scientific debate
The common ground includes:
• That climate has always changed and always will.
• That CO
2
is a greenhouse gas, the accumulation of which results in warming of
the lower atmosphere.
• That post-industrial human-related emissions comprise a new source of
atmospheric CO
2
• That a global warming of around 0.7°C may have occurred in the twentieth
century.
• That global warming has ceased over the last seventeen years.
The three key science issues remaining in dispute are:
• The amount of net warming that is, or will be, produced by the 'extra'
human-related emissions.*
• Whether any actual evidence exists for dangerous warming of human causation
over the last 50 years.
• Whether the IPCC's computer models can provide accurate climate predictions
100 years into the future.
