Note: This opinion piece was written before the Pike River Mine explosion.

For 35 years I have been wrong about how to prevent climate change. It's time I confessed.

For 35 years I have worked to improve energy efficiency - insulating homes, efficiency standards for appliances, better light bulbs, fuel-economy standards for cars and energy-saving technologies in industry and farming.

The assumption was that this would result in less fossil fuel being burned and less carbon dioxide going into the atmosphere. Well, it doesn't.

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For 35 years I have promoted renewable energy - solar water heating, solar electricity, wind power, log and pellet burners, bio-gas - assuming that these would result in less fossil fuel being burned and less carbon dioxide going into the atmosphere. Well, they don't.

We would be stupid not to make those changes, which achieve cost savings, health benefits, warmer homes, jobs, more affordable energy, more profitable businesses and a stronger economy. But to protect the climate, we have to change tack. I'm changing tack.

Imagine you own a coal mine or an oil field, and demand for your product drops because people are using alternatives. Do you shut up shop? Not likely. Your job is to ensure that those resources get burned one way or another. So you look for a whole new use for the resource.

The key issue for the climate is how much greenhouse gas we allow to accumulate in the atmosphere. That total depends on how much fossil fuel is mined and determines whether we cross the tipping point into dangerous levels of warming, with associated ice melt, acid oceans, storms, droughts and floods.

We are focused on annual emissions to the atmosphere. We need to focus on how much of the total stock of oil, coal and gas in the world we can burn without destabilising climate, and therefore how much must be left in the ground forever.

Leaving a resource in the ground forever goes against the grain - our whole history and culture is built on making use of resources. It sounds daft to deliberately leave economically recoverable resources unmined. But let's get used to the idea, because our survival depends on it.

Nasa climate scientist James Hansen has calculated how much more fossil fuel we could afford to use if we were to get back to 350 parts per million of greenhouse gases in the atmosphere: the level that he calculates will allow climate to stabilise.

His recipe, set out in his book

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Storms of My Grandchildren

, published last year, allows us to use all the conventional oil (though not tar sands, shale or oil from extreme environments like that of the Southern Ocean) but coal must be phased out completely by 2030, starting now.

New Zealand is heading in the opposite direction. In addition to oil and gas exploration there are well-advanced plans to use more than 3 billion tonnes of economically recoverable lignite from three fields in Southland. These plans are big, and New Zealanders are hardly aware of them.

Because we don't need coal for electricity; state-owned coal company Solid Energy has developed plans to use the lignite for fertiliser and diesel.

This is why changing your light bulbs will not reduce greenhouse gases - Solid Energy, and its government owner, are determined to use that coal.

The company wants to build a pilot plant next year to make briquettes, taking the water out of lignite so it burns cleaner and hotter (but with no less carbon emissions) for Fonterra's milk-processing plants and for export.

The pilot plant will produce "only" 100,000 tonnes a year of briquettes. The full-scale plant would be many times larger.

Next off the blocks is a plant to convert coal to crude oil and/or diesel. They claim it could produce all New Zealand's diesel this way. Depending on the technology used, it is likely to double the carbon emissions of every litre of diesel compared with petroleum-sourced fuel.

The third leg of the trifecta is coal to urea, a nitrogen fertiliser. More urea means more cows per hectare, so more effluent in rivers and more nitrous oxide emissions - another powerful greenhouse gas.

Solid Energy say all the emissions will be "offset". But increasing the amount of biological carbon that cycles between atmosphere and plants can't compensate for putting more fossil carbon into the system, even if our ETS scheme pretends it can.

Paying money is, in the end, not a get-out-of-jail-free card for increasing pollution.

These huge lignite developments are close - Solid Energy intends to start building next year. Any hope we had of reducing our greenhouse emissions would be lost.

We need to refocus international negotiations to keep most of the world's remaining coal in the ground. As citizens, we need to refocus our domestic action to tell Solid Energy and the Government by every means available to us to keep the coal in the hole. Every tonne of lignite New Zealand keeps in the ground is 1.5 tonnes of carbon dioxide that doesn't get into the atmosphere.

We can let energy efficiency give us a good standard of living, a prosperous economy, more jobs and a clean, green marketing brand. But if we mine the coal, we are fooling ourselves that those "green" developments will do anything for the climate.

* Jeanette Fitzsimons, former Green Party co-leader, retired from Parliament last year.