The burning of fuels such as oil coal and gas produces carbon dioxide. This gas is an essential part of the life cycle on earth. If there weren't carbon dioxide in the air, most plants and animals would cease to exist. The negative effect of carbon dioxide is that high concentrations in the atmosphere reduces the amount of heat radiated from the earth into space, this causes the temperature of the earth to rise.
The problem is the accuracy of the computer models used to forecast how much temperatures will increase in the next 100 years. These computer models are huge, yet they still have to rely on assumptions about future use of energy, population growth, economic growth, and efforts made by humans to reduce the output of carbon dioxide. I think some of the forecasts have been too pessimistic, especially those produced by pressure groups with an axe to grind, such as Greenpeace.
I believe the world will get warmer, but it won't be the catastrophe that the doom-mongers predict. In fact, cooler countries in Northern Europe, such as ours, may be less affected by global warming than poorer countries nearer the equator.