Global warming is one of the predicted results of increased greenhouse gas concentrations. It's like if you were to put double glazing in the windows or thicker insulation in the walls of your house, but kept the heating on at the same level, it would get warmer. On the most basic level, it really is that simple. On Earth, the sun is our source of heat and infrared radiation pssing through the atmosphere is the way heat is lost. A greater amount of carbon dioxide reduces the heat loss, causing the temperature to rise.
The effects are very unliikely to be confined to global warming. There will be effects on rainfall, winds and temperatures in different regions as well, but these are harder to predict. Sea level rise appears predictable, too on the current evidence.
As a result of the scientific research that has been carried out, more and more subtle natural influences on all aspects of the climate are being better understood by scientists. Many knock-on effects to human influences, by means of CO2, other gases and a variety of other factors have also been identified.
Despite many attempts by scientists who are respected in the field, such as Dr Lindzen, to identify processes which may negate the effects of human influence, the basic conclusion and the process responsible for it (the greenhouse effect) have remained unchanged for decades now.
Sceptics/denialists/contrarians/propagandists make a lot of noise, especially on the internet, but the fact is that no contrary scientifc theory (that the climatic effects of anthropogenic greenhouse gases will be negated by other physical processes or that the greenhouse effect is somehow a flawed theory) is favoured by the existing evidence.
This still leaves room for some to claim that an undiminished greenhouse effect is rendered insignificant by climatic changes instigated by natural processes. This is often pretty close to saying that the consequences of climate change 'don't matter', or don't matter as much as the inalienable rights of individuals to burn as much fuel as they want. However, no natural processes have been found to account for the observed temperature changes of the last century and, with the exception of extremely rare catacysms and the ice ages of tens of millennia, no natural sources of temperature change over decades and centuries of comparable magnitude globally have been identified.