Three Cultures of Climate Science

The British physicist and writer C.P. Snow famously distinguished between "the two cultures," the sciences and humanities, deeming the split a major impediment to the solution of social problems. As scientists and the general public grapple with global warming, that split is getting renewed attention--to scientists it seems that the public has trouble grasping what they're saying and acting accordingly, while to the public scientists often come across as high-handed or even authoritarian. There's a lot to be said about all that, but that's not the end of it. Even within science there are subcultures, and members of those subcultures do not always see eye to eye about what's most significant, credible, or--in terms of action--decisive.

Students of climate science conventionally distinguish between three subfields: theory, empiricial work, and modeling. The modelers tend to get the most attention, because they are the ones who assess how sensitive global temperatures have been to greenhouse gases and assert how much warmer the earth will get as concentrations of carbon dioxide, methane, and other gases increase in the atmosphere.

One effect of that focus on modeling is that people tend to lose sight of the basic theory and its history, starting with the French physicist and mathematician Joseph Fourier--best known to electrical engineers for the Fourier Transform, ubiquitous in signal processing--who discovered the greenhouse effect in the early 19th century. More than a hundred years ago the Swede Svante Arrhenius came up with a credible estimate of how much the earth would warm in reaction to a doubling of carbon dioxide in the atmosphere. In the meantime, the warming effect of various gases has been definitively proven in the laboratory.

And that brings us to something else that follows from the focus on modeling. Computer simulations, however elaborate and whatever their horsepower, always are open to claims that something important has been left out, some key parameter has been misestimated, or some critical connection misunderstood. Models always are so complicated that they basically have to be taken on faith by anybody who's not a modeler. For this reason, a lot of scientists and many members of the well-educated public much prefer empirical work, where one can understand at least in principle the scientific basis of claims.

This is why, in the last analysis, the hacked (or allegedly hacked) e-mails to and from climate scientists at the University of East Anglia have been getting so much attention. As scientist John Christy explains in an interview with IEEE Spectrum, East Anglia has played a key role in formulating the recent history of the world's temperature, and if that history has been misrepresented, then a case can be made that recent warming is mainly the result of natural cycles, not emissions from human activity.

The most recent thousand years of climate history have received enormous attention primarily because of Michael Mann's famous hockey-stick graph, which shows a sharp increase in global temperatures in the last century, by comparison with the thousand-year average. It's the authenticity of this graph that is being called into question--not for the first time. The hockey stick graph was reproduced in the 2001 report of the Intergovernmental Panel on Climate Change and no double had a big impact on opinion primarily because it is so easy to look at and understand.

But there have always been students of climate science who thought that too much emphasis was being put on the recent history of the climate record, at the expense of the million-year record gleaned primarily from ice cores. The ice drillers have established a lockstep relationship between greenhouse gases and global temperatures, through numerous ice ages and interglacial transitions: when carbon dioxide and methane levels are high, we live in a nice balmy world like today's, and when they're low, we have an ice age. Though it's not crystal clear what's driving what, this much is well established: greenhouse gas levels today are far higher than they're ever been in the last million years, and the difference between pre-industrial and today's levels is greater than the difference was between glacial and interglacial levels.

That's what gives a lot of people pause.

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