Watson on the role of scenarios in policy making

In a paper for the Philosophical Transactions of the Royal Society of London published in 2005, Robert Watson, former IPCC chairman, has some interesting thoughts about the relation between science and policy. He thinks that scenarios are the crucial tool to influence policy makers:

 ‘Besides direct observations of change, one of the most important tools for helping to foster policy changes are plausible future scenarios. In most of the scientific assessments mentioned above (e.g. stratospheric ozone depletion, acid deposition and climate change), the use of scenarios has played an absolutely critical role in describing plausible future changes and identifying the implications of different policy choices and convincing policy-makers to take action.’

This indicates that it is scenarios, not models that are the important tools to convince policy makers. What are they? Watson says:

‘Scenarios are plausible futures, not predictions or projections of the future. The initial step is to develop a set of internally consistent storylines among the various indirect and direct drivers of change, which are then coupled to environmental models … that link the various drivers to the probable consequences.’

At this point the picture gets blurry. On the one hand I see a layer of different things, starting from the bottom with story lines (what are these?), upon which scenarios rest, which are used to develop projections (by applying modelling techniques), from which the most probable are singled out as predictions (this is how I interpret the difference between predictions and projections, based on the IPCC definitions as per previous posts on this blog. Correct me if I am wrong!).

So it is story lines--> scenarios--> projections--> predictions.

On the other hand I also read that there are several story lines which are coupled to models that ‘link the various drivers to the probable consequences’. In this reading, scenarios are the product of drivers that are modelled in a certain way to give us probable consequences. Are these probable consequences scenarios or projections? I probably need to understand better what the word driver means here. Watson says:

‘The main drivers are changes in: (i) the economic system (e.g. economic growth, purchasing power parity, globalization, trade liberalization, privatization, structural adjustment policies and subsidy regimes); (ii) demography (population size, the rural to urban migration, family size, age structure and gender status); (iii) science and technology (e.g. public and private sector funding for research, technological advances in biotechnology and information/communications and technology transfer); (iv) socio-political systems (e.g. multilateralism, regionalization, security, balance of power and migration); and (v) individual and community behaviour.’

Ah. This sounds familiar to me, as it is all social and political. So in order to understand plausible futures, we need to understand the society we live in. This is a brilliant insight, if somewhat surprising given that the paper was published in the Biology Sciences Series of the Royal Academy. Is Watson really saying that in order to influence policy makers about climate change, all we need to understand and control are the above factors? No GHGs are listed, presumably they come in through the models? But why are zero carbon technologies missing from the list? They surely would be central, wouldn’t they?

Does anyone know how this would relate to the way the IPCC sees its policy advice and the role models play? Does anyone know if Watson has a decidedly different view than the IPCC (perhaps after he left in 2001?) While he mentions Integrated Assessments, no mention is made of GCMs.