Geoff writes (& I comment below):
There are two issues here:
1. Is the world heating up?
2. If so what is causing it?
It is a fact that there is a higher concentration of CO2 in the atmosphere than there was 30 years ago. Currently the content is 391ppm by volume. 30 years ago it was about 338ppm. 50 years ago it was 315ppm. These facts are by observation and not from computer models and so I am sure you will have no argument with them.
CO2 is an important constituent of the atmosphere as it absorbs and emits IR radiation. This is designed (by whom we may argue about!) to stabilise the earth's temperature. However as the concentration increases, the balance of stabilization is thrown and it starts to act as a blanket, thus causing the world to heat up. i.e. the IR emitted from the earth is reflected by the C02. As in any feedback control system, which clearly this is, there are hysteresis (a delayed response by an object to changes in the forces acting on it, especially magnetic forces) gaps and this is probably why it might be possible to observe, at times, the temperature going up before the C02 concentration increases.
You can probably prove the above by a simple experiment at home if you could assemble a greenhouse, a bottle of C02 and a thermometer!
What causes the C02 concentration to increase is not so clear cut but there is no doubt that we are pumping more C02 into the atmosphere than we did by way of vehicles, ships, aircraft and industrialization in general.
I think there are more than two issues.
Is the world heating up?
The temperature of the globe fluctuates. It has risen somewhat since the end of the Little Ice Age – and good thing too, from my perspective.
What is causing it?
There are a number of candidates. One is solar activity, over which we can never hope to have any control.
Should we be worried – so worried that we should spend trillions on dismantling the world's economy?
The warming that has occurred is not catastrophic and seems to have stopped in the last decade or so.