A New Zealand economist is promoting a massive worldwide programme of planting crops and burying charcoal to avoid catastrophic global warming.

Dr Peter Read, a researcher at Massey University, has just convened a workshop sponsored by international agencies in Paris to stave off what he calls "the mother of all catastrophes".

He told the New Zealand Sustainable Energy Forum in Wellington on Saturday that the Earth's climate had warmed suddenly by 5C in only a decade or so several times in the past 400,000 years, when gradual processes tripped into abrupt climate changes.


He said the Kyoto Protocol, which requires most developed countries to cut back their emissions of global-warming "greenhouse gases" to slightly below 1990 levels, might be too modest to avoid disaster.

In contrast, a massive global programme of planting crops and ploughing organic matter back into the soil could cut carbon dioxide back to pre-1800 levels - and feed poor countries at the same time.

Carbon dioxide fluctuated between 180 and 280 parts per million in the atmosphere through climatic cycles for millions of years until about 1800, but emissions from industry and cars have now pushed it up to 374 parts per million.

Scientists fear that continued warming, and gradual melting of the polar ice caps, could tip the planet at some point into much more dramatic changes.

Ironically, these could include plunging Europe into a new ice age if the polar meltwater reverses the Gulf Stream, which now carries warm tropical water to the North Atlantic. At the same time, parts of the tropics could become too hot and dry for farming.

Dr Read said human activities were pumping out 8 billion tonnes of carbon into the atmosphere each year.

But this was only a fraction of the 110 billion tonnes of carbon that were emitted and recycled through the atmosphere each year through the natural processes of plants, animals, soil bacteria, volcanic activity and weather.

"So is it more sensible to increase terrestrial absorption by 4 per cent [to halve net carbon emissions], or to cut industrial emissions by 50 per cent?" he asked.

He said there was no shortage of land that could be used to grow forests or fast-growing crops such as sugar cane - roughly 2 billion hectares of grassland and open woodland, compared with only about 1.5 billion hectares of land that was cultivated already.

The trees or crops could be turned into ethanol or biodiesel and used for energy, replacing long-buried organic matter energy sources such as coal and oil.

The carbon emitted in using bioenergy would be absorbed from the air again when the crops were regrown - in effect simply speeding up the natural cycles of the existing slow-growing grasses and woodlands.

Moreover, the charcoal left over after burning a crop to cook food, for example, could be buried again to fertilise the soil.

"The charcoal retains water and nutrients, providing a [base] for fungal and microbial activity essential for fertility," Dr Read said.

"Another technique, developed by Canadian researchers, is to actually make new soil with an overlay of 'ramial' wood chips.

"Ramial wood, from the twigs and small branches of deciduous trees, is chemically different from trunk wood. It gets broken down by naturally occurring white fungi and the carbon content gets mineralised in new soil."

He said this would not happen on the scale required unless governments took a lead by requiring part-ethanol and biodiesel blends in cars.

Governments could also use the carbon trading system being set up under the Kyoto Protocol to give credits to developing countries that planted bioenergy crops and buried the charcoal.

What can be done

* Grow forests or fast-growing crops such as sugar cane.

* Turn the trees or crops into ethanol or biodiesel.

* Use left-over charcoal for fuel, or bury it to fertilise the soil.