ECONOMICS is not the most popular profession in the community.

Although they're well-meaning practitioners, economists are often derided for assumptions and findings that seem to bear little relation to the real world.

Two recent examples have done little to change this.

One was Federal Treasury's economic modelling on the impact of an emissions trading scheme.

It concluded, contrary to what many believe, that an ETS would have minimal economic impact, including on agriculture.

How could that be? Farming is the nation's second largest emitter of greenhouse gases and with input costs also certain to rise, surely there'd have to be some reasonable pain?

Not in Treasury's world. Sheep and cattle industries will still register growth, albeit less than they would have, while dairy and grains will actually benefit.

The main reasons? Treasury assumes most other nations will also be implementing ETSs and that our farmers will plant plenty of trees and simultaneously lift productivity by nearly 4 per cent a year over the next decade.

There are real doubts about the first assumption, and as for farm productivity growth, its been on the wane and is running at barely 2 per cent a year. What's going to magically double it from 2010?

Even with a massive R&D effort, it's a big ask. Hopefully, the Rudd Government considers Treasury's view, as it does those of its chief climate change adviser Professor Ross Garnaut, as "just one input" into its ETS deliberations.

Then there's the latest offering from the Australian Bureau of Agricultural and Resource Economics.

In mid-September, ABARE predicted a national wheat harvest of 22.5 million tonnes, based on the "good timing" of generally below-average winter rain.

Crops were in a "reasonable position" leading into spring, ABARE said.

Industry people on the ground were incredulous. One was Keith Perrett, the Government's chief adviser on drought conditions, who'd been travelling extensively across the nation's grain belt.

The wheat crop would struggle to reach 20 million tonnes, he said.

Last week, ABARE issued a revised forecast - 19.9 million tonnes - reflecting the lack of spring rain.

For some, including Perrett, that figure might have been right in June, but not now.