[sien]

Economics forecasting is harder than the weather.

How do you build an economic model that can deal with the introduction of mobile phones? What about some new energy source that cut the cost of energy dramatically? What about the fall of Communism?

Also the weather doesn't have expectations that react to the weather forecast. Economic models get incorporated into people's expectations and this feedback can actually alter the economy. If you read up on The Phillip's Curve and stagflation you can see an example of this interaction.

Weather is actually decent for forecasting. You can constantly get new data to verify your model against. If you are forecasting for a week you have hundreds of tests to do per week.

Any forecasting where the predictions matter over the scale of decades is harder because the time span means you will have less data available for validation.