The
first complication is that scientists - all of us really - have to accept that the decisions we make are not entirely determined by data and reason. They are, or should be, influenced by data and reason, but our decisions are inescapably bound up with the representation of the world that we carry in our head. So if we want to influence public opinion and public policy, we have to hire professionals to help us make sure we construct the right representation of the world.
But what is the "right" representation? That's the second complication.
Science is really good at data, evidence, and reasoning. That's the reflective thinking embodied in "Data rule!" It's not good at distinguishing right from wrong or good from evil. Philosophers argue about whether
David Hume was right. Some argue that it is possible to develop a purely
naturalistic ethics derived from empirical facts about the world. Others argue that ethical principles derive from other sources. Regardless of which side is right, it's safe to say that it isn't easy or straightforward to go directly from a scientific statement - "The global average temperature will be 2°C higher in 2050 than it is now." - to an ethical or policy statement - "We ought to reduce global emissions of carbon dioxide to 1990 levels or below by 2020".
That puts the IPCC into a real bind. As scientists, the IPCC can provide a solid assessment of the likely trajectory of future changes in climate and of the likely impacts associated with those changes. It can even identify the technologies that might be needed to adapt to future climate change and the costs associated with different strategies for adapting to climate change or to reducing the magnitude of climate change or both. What it can't do is to determine which of those strategies is preferable or ought to be adopted. Those choices will involve questions of value - What kind of a world do we want to live in? What responsibility do developed countries have, given that they are responsible for most of the greenhouse gases in the atmosphere? What responsibility do emerging economies have, given that they will be the source of most future emissions?
Unlike an advocacy organization, the IPCC can't identify a preferred policy outcome and organize a campaign around that, including a representation of the world that supports that policy outcome. Instead, its objective must be something more nebulous and less definite. Its objective must be to provide the public and policy makers with an intuitive grasp of the earth's climate system and with tools to guide their reasoning that are consistent with the scientific details in the 5th assessment report. And because climate science has become so deeply politicized, they must find a way to do so that is open and transparent - a daunting, but vital task.
If I had good ideas on how to accomplish it, I'd offer them. Right now, I can diagnose the problem. I can't suggest a cure.