The IPCC consensus is best viewed from the Hadley research centre's site at at WG1: http://www.meto.gov.uk/sec5/CR_div/ipcc/wg1/ipcctgc.html
However, to gain its widespread acceptability the IPCC has had to err on the side of conservatism, and if an effect is suspected but is with the present state of knowledge unmodellable, they normally mention it in their text but ignore it in their modelling, scenarios and forecasts. The most important set of issues in this area concern feedbacks. There are many poorly understood feedbacks, including some that are negative - ie stabilising, but also a number that are positive and capable of making the future much worse than the IPCC's suggestions.
Climate change is a survival issue due to the risk that positive feedback processes will magnify the initial global warming due to anthropogenic greenhouse gases. Historical records show that climate changes not smoothly but in sudden jumps, due to the balance of positive and negative feedbacks. These can be both physical and biogeochemical processes, and the latter are still not included in most "Global Circulation Models" on which the IPCC projections depend. A recent report distributed by the Hadley Centre at Cop6 in November 2000 has started the process of incorporating some of these feedbacks into their modelling work. The results are chilling (that is to say, planet-warming), though still not incorporated in the majority of even Hadley's own models. See www.metoffice.gov.uk/research/hadleycentre/pubs/brochures/B2000/index.html. We must expect of surprises, abrupt changes and possible catastrophes if we continue to emit so much CO2.
The large JPEG Graphic below illustrates briefly the best known climate feedback processes. If you cannot view this graphic, you can also find a list of these feedback processes towards the end of GCI's protocol proposals: 2.14 Strengthen research into Climate feedback processes
By this term we mean the sundry assortment of proposals to, for example, deflect solar radiation with mirrors or seed the oceans with massive amounts of iron filings. Such proposals all have the characteristics that they are profitable, risk global-scale catastrophic side-effects, and divert everyone's attention from the essential need to reduce emissions. Our colleague Ben Matthews has published an extensive critique, available at: http://www.chooseclimate.org/cleng/mf.html. David Keith at Carnegie Mellon University has also published extensively on this topic (see http://www.andrew.cmu.edu/user/dk3p/) and advocates caution before undertaking such exercises.
Note that allegations are now afoot (autumn 2000) that the USA is already indulging in climate engineering by seeding the upper atmosphere with large quantitities of white powder. GCI takes no view as to the veracity of these allegations. See http://www.chemtrailcentral.com for details