William Worsley's family business took a bit of a knock when the Royal Navy stopped building ships out of oak, so he is not your average farmer. One day, he will inherit a baronetcy and a portion of the village of Hovingham, where his branch of the Worsleys has lived for 450 years.

Meanwhile, he has to work to keep the roof on at Hovingham Hall, which dates back to 1770, and to keep about eight people employed in the farming and forestry on his father's 730 hectares next door to Castle Howard.

He also has a part-time job as deputy president of the Country Land & Business Association, which he takes seriously. He is proud of the "intellectual rigour" of CLA politics and the fact it set up its first working party on climate change in 2001.

The CLA went on to produce the first computer programme designed to measure the environmental impact of farming – Climate Accounting for Land Managers (CALM).

After complaints over its operation the CLA acted and the latest version of CALM is now out for assessment. Mr Worsley was one of the first to try it and we meet to discuss his results, which are...

Emissions – equivalent to 760 tonnes of carbon burnt in a year.

Sequestration – equivalent to 3744 cubic tonnes of carbon extracted from atmosphere.

Carbon balance – 2984 tonnes in credit.

This happy result is unlikely to be matched by many. A mixed farm in Bucks, with 590 dairy cows and followers on 647 hectares, gets an out-turn of 1327 cubic tonnes in uncompensated emissions.

A Cambridgeshire arable operation, on 688 hectares, goes into the red by 770 tonnes, according to the same programme.

It is too early to say what is standard and what is exceptional. However, it will not be long before everyone in farming needs to know.

Defra has already persuaded the dairy industry to agree to reduce its emissions a third by 2020.

The dairy industry does not even know what its emissions are, yet, but a cow emits methane from one end and nitrogen from the other and both make a substantial contribution to the 'greenhouse effect' which is blamed for global warming.

The CLA calculator translates all relevant emissions into carbon equivalents, because that is the common currency of greenhouse debate.

The Hovingham Estate gets off relatively lightly on livestock emissions. It does let some summer grazing for 75 cows and a similar number of sheep, but sheep are not so bad and the cattle figures are spread over a year and a lot of acres.

So far, the only way to significantly reduce methane from cattle is to take them off grass and feed them a special diet indoors, although experiments are in progress – believe it or not – in ways to make them less flatulent in the field.

So far, Mr Worsley is more interested in getting his grass cut on the cheap.

But the cattle make a significant contribution to his carbon footprint and he can foresee a day when he might have to think about that.

One day, almost certainly, farming will be working to a carbon target and farmers will have to earn or buy enough carbon credits to meet their licence conditions. And low-carbon operations like Hovingham will be able to sell spares to other carbon-capped businesses.

The other big farm operation on the estate is growing cereals, rape and beans, which need fertilisers containing nitrates, which run up black marks because they cost oil to extract from the ground and produce nitrous gases when washed off crops.

"But you would be careful with them anyway," Mr Worsley comments. "Fertiliser is expensive, in cash, let alone environmental terms.

"Any that doesn't get taken up by the crop is wasted." It does not matter if you believe in "global warming" or not, he says. The politicians do, so farmers will have to.

"Anyway, it's good business management," he says.

"It is a way of monitoring and managing your consumption."

His farm manager, David Blades, and head forester, David Brown, say it probably took a day to collect all the necessary records but less than half an hour to finish the questionnaire.

The calculation excludes tenanted farms on Worsley land, which are responsible for their own emissions.

It also excludes Hovingham Hall, which is a domestic residence, because the estate has its own offices, administering about 1800 acres, split roughly half and half between farm and woodland. Working all that costs...

27,400 litres of diesel, which equals about 72 tonnes of carbon.

15,000 kw hours of electricity, which equals about 8 tonnes of carbon.

200 litres of petrol, which equals about 1 tonne.

And so it goes on –
estimated emissions from land rented out to a potato grower; estimated carbon storage value of leaving some ground undisturbed; tonnage of fertilisers; fuel burnt by the harvesting contractor and the straw baler; and so on.

The saving grace is, of course, the forestry operation. Young trees store even more carbon than old ones and the estate is planting 33,000 a year.

But it takes 40 years to get a financial pay-off from a tree – even a fast-growing softwood. An oak needs 140. It takes ancestral commitment to bother with both.

To some extent, the forestry is subsidised by pheasant shooting.

So far, the CALM formula makes no attempt to measure the carbon footprint of that. But the Yorkshire Post left Mr Worsley musing on the challenge.

Meanwhile, he is keen for as many farmers as possible to take a free run through the CALM program at cla.org.uk