Licence discussion and references
Various people have questioned the WordWeb licensing terms. It is true that targeting flights is a very crude measure; many people's CO2 emissions come mostly from their home due to inefficient heating, insulation or air conditioning. However the licence is designed to be easy to understand, and sufficiently simple that people will know immediately whether or not they satisfy it. If you break the licence you are certainly responsible for more emissions per person than are sustainable, and you can certainly afford to buy the Pro version. The licence is not telling you what to do: that is up to you, but if you don't satisfy the licence you need to pay to use the program.
What is needed is swift and effective action at government and international levels. Climate change is the "market failure on the greatest scale the world has ever seen" [Stern 2006] - market forces and personal action alone will not solve the problem. However personal action can help. In particular if demand for aviation can be reduced now, that will make it easier for governments to make cuts later as well as reducing a significant source of high-altitude emissions today. Cuts in emissions now will (statistically) save lives later; even the most ambitious international plan to curb emissions will not prevent a significant and damaging rise in temperature.
Almost all studies more than a couple of years ago were extremely optimistic about the impacts of climate change, for example neglecting important feedback mechanisms that could lead to very rapid warming: there is still a significant risk of it being much worse than suggested by current studies. Temperature increases in excess of 5 degrees are quite possible if nothing is done. Even the best-case scenario involves major negative consequences in a few decades.
Even conservative studies suggest that stabilization will require cuts of around 80% from current levels of CO2 emissions. This number comes from the Stern Review (see references). Continuing with business as usual will result is something like a 5%-loss in global GDP and cause many hundreds of millions of people to face starvation and disease due to shifting weather patterns. To have a good chance of avoiding the worst outcomes, cuts of at least 60% in total emissions are needed by 2050, with significant progress in the next decade; it is much more effective to reduce emissions early on than make huge cuts later on when the problem starts to get out of hand.
Tackling aviation growth is particularly difficult because of international agreements not to tax aviation fuel. There is also considerable pricing flexibility (price elasticity of demand), meaning that prices would probably have to at least double to cut flight use in half. This corresponds to an infeasibly high carbon emission trading price. In the absence of any effective governmental legislation to restrict aviation growth, WordWeb's licence is a small way to increase the cost of flying and, more importantly, to increase awareness of the problem.
Taking numbers from the Stern Review: every medium distance flight you take now causes about 0.001 people to face starvation in the future. Roughly this means that for every hour you spend flying, someone in the future will spend an extra day short of food.
What has this to do with WordWeb?
Some people feel that this has nothing to do with WordWeb, and the licensing terms are ridiculous. We agree the situation is ridiculous; the WordWeb licensing is just reflecting the current huge under-pricing of air travel. Every time you fly you are not paying the cost to the environment (and hence other people); in economics terms climate-changing emissions are an important externality leading to a market failure. WordWeb is trying to slightly increase the cost of flying via its licence to correct for this anomaly. If and when air travel is charged correctly to reflect the total cost, which is much the most efficient solution, the WordWeb licence will be changed to a more sensible economic model.
The licence also has the advantage that people who cannot easily afford to pay can use the program for free. If you can afford to fly, so that you do not satisfy the licence, you can afford to buy the program.