[link|http://physicsworld.com/cws/article/news/30711|PhysicsWorld]:

Most of the evidence for human-induced or \ufffdanthropogenic\ufffd climate change has come from climate models, which simulate the dynamics of the atmosphere using complex fluid-flow equations. Given inputs of temperature and other climate data from instruments and older proxy records, such as tree rings, these equations are solved numerically using short time increments.

Although all climate models indicate that the Earth\ufffds temperature will continue to rise, some climate-change sceptics have suggested that the anthropogenic influences are exaggerated. For example, because the simulations divide the atmosphere into a 3D lattice with a coarse resolution, they cannot take into account the effects of clouds, which can both reduce or enhance warming.

Rather than trying to simulate the atmosphere as climate models do, Verdes has used statistics to assess man\ufffds role in climate change.

[...]

From the Physical Review Letter article (P. Verdes, PRL 99, 048501 (2007)):

Summing up, in this work we have taken advantage of a remarkable result from the theory of nonlinear time-series analysis, namely, that it is in practice possible to estimate the variation of external driving forces acting on complex systems even when their internal mechanisms are unknown, to study the attribution problem in climate change from a different perspective. Using two independent methodologies for accurate driving force reconstruction and different data-driven modeling tools, we have presented evidence that the forcing agent on global climate dynamics can be consistently identified with the combined effect of anthropogenic emissions. The present study is particularly interesting in that it represents a new approach to this important problem. Furthermore, it is purely data-driven and thus avoids any possibly unaccounted mechanisms of first-principles general circulation modeling. We believe this is a distinctive aspect that can enrich the continuing debate on the future of our climate

Neat.

Cheers,
Scott.

Unfortunately, AIDS wasn't discovered until 1981. The graph below shows that the rapid rise in the necessary "driving force" started around 1965. So it couldn't have been AIDS.

[image|http://images.iop.org/objects/physicsweb/news/11/8/2/DrivingForce.jpg|0|Climate Change Driven by Anthropogenic Factors|399|500]

But you get the general point. If you think the driving force for climate change is widgets, all you need to do is have data on widgets for the last 150 years and compare it to the observed temperature. If there's a statistically valid relationship, then there may be reason to investigate that factor further.

The power of this paper is that it shows you don't need to have a detailed understanding of the mechanism/model for the system to see whether a particular factor may be an important driving force or not. You can treat the biosphere as a black box and just look at the inputs and outputs.

For instance, one could compare the rise in temperature with the global population. If a correlation is observed, one could then speculate on why that correlation exists and look at various factors that may contribute.

Cheers,
Scott.