Elaborating on work discussed here before, Gavin Schmidt provides some information on what distinguishes the most recently developed sorts of climate models for their predecessors, such as General Circulation Models. The newer Earth System Models:
now include interactive atmospheric chemistry, aerosols (natural and anthropogenic) and sometimes full carbon cycles in the ocean and land surface. This extra machinery allows for new kinds of experiments to be done. Traditionally, in a GCM, one would impose atmospheric composition forcings by changing the concentrations of the species in the atmosphere e.g. the CO2 level could be increased, you could add more sulphate, or adjust the ozone in the stratosphere etc. However, with an ESM you can directly input the emissions (of all of the relevant precursors) and then see what ozone levels or aerosol concentrations you end up with. This allows you to ask more policy-relevant questions regarding the net effects of a particular sectorâ€™s emissions or the impact of a specific policy on climate forcing and air pollution.
Atmospheric chemistry is clearly a highly complex field. This makes it all the more strange and troubling that such a vast divide exists between debate between experts in the scientific community and debate within society at large.
That said, I suppose these situations arenâ€™t really all that rare. Serious geologists and biologists continue to work out the minutiae of the history of present status of the Earth, at the same time as laypeople and self-styled â€˜expertsâ€™ maintain debates about whether the world is 6,000 years old and whether all the creatures on it have existed since the beginning of time. By the same token, no matter how sophisticated scientific modeling of the climate becomes – and how much data accumulates demonstrating human-induced warming – there will still be people willing to baldly assert that climate change isnâ€™t happening / is natural / isnâ€™t a problem / is beneficial / is caused by sunspots, etc.