My M.Sc. project is looking at the effect of global warming on tree physiology and I use a lot of emission/ climate change models that deal with the temperature increase with a certain PPM increase in C02 concentration. The main piece of evidence that warming is a result of human influence is the increase in CO2 levels. Since 1950, CO2 concentrations in the atmosphere have increase from 310 PPM to 360 PPM. These are the highest levels in 400,000 years and this increase has occured in direct positive correlation with the industrial era and major deforestation. This increase in 50 years normally occurs over thousands of years under natural climate change.
People bring up temperature shifts in the past. These were not the result of CO2 spikes, they are a result of other forces. The temperature increase we have seen in the past century (1 C) on a global average occured at a rate much greater than what normally occurs.
People also say 1C is nothing and that is doesn't really matter. That is a global average and locally, especially at polar latitudes, temperatures are forecast to increase much more than that. This leads to increase in glacier melting, leading to more water in the atmosphere from evaporation. This then adds to the effect as water vapour also contributes to warming. This is a cycle that builds itself and accelerates once it gets going. If we can stop that cycle or at least delay it, we may be able adjust.
I do agree though that Kyoto itself will not make much of a difference but IMO is more of an awareness campaign to make countries and people think about what they are doing. It is a start to going in the right direction. Countries that are unwilling to participate in Kyoto should be subject to taxes or tariffs on goods that they export as these goods were not manufactures under Kyoto requirements. This would balance the economic benefit of not participating. The money from taxes and tariff would then be redistributed across countries that are participating in Kyoto.