MELBOURNE: So we've finally agreed that climate change is a serious problem and we need to slash our greenhouse gas emissions. But how do we do it? Is the solution solar? Or nuclear? Or perhaps wind? Or something else?

One of the problems with the solutions debate - and this isn't a recent phenomenon - is that addressing climate change has often seen one technology pitted against another.

A recent Australian survey found some 50 per cent of the population think solar should be used to solve the problem. Solar proponents tout its obvious benefits - the community loves it and it generates clean, renewable energy with no greenhouse gas emissions. But critics point to the fact that it only works when the Sun shines, is expensive and will never replace coal since it cannot meet our baseload power needs.

But while critics of solar are absolutely right that it will never replace all our coal and gas-fired power stations, they are misguided in dismissing solar as unimportant. And with the handing down of the report by Ziggy Switkowski - who led a taskforce commissioned by Australia's government to look at feasibility of nuclear power for the country - some now think nuclear is the answer. But anyone seeking a cure-all is bound to be disappointed.

The problem with this debate is that people are providing answers when we haven't clearly defined the question. Solar or nuclear could both be the answer - it depends on how the question is phrased.

A great way to get one's head around what the question may be is to look at a study by Steve Pacala and Robert Socolow from Princeton University in New Jersey (read more). They examine the action needed to stabilise emissions at today's levels within 50 years. We currently emit around seven billion tonnes of carbon and this is forecast to double in 50 years. So this represents a need to cut emissions by around seven billion tonnes of carbon each year by 2050. The researchers then break this seven billion tonnes into seven wedges, each of one billion tonnes. So the question becomes: what is needed to cut emissions by one billion tonnes by 2055?

The best place to start is to reduce demand - this saves money and cuts greenhouse gas emissions. There are many opportunities for reducing emissions by increasing efficiencies in the three major sectors of the energy economy: electricity production, transportation fuels and direct use of fuels in residences and industry.

A billion-tonne wedge would be achieved in the transportation sector if the fuel efficiency of all cars projected for 2055 were doubled. A wedge could also be supplied if best practices were used in all residential and commercial buildings by 2055. In the electricity generation sector, we would need around 1,400 natural gas electric plants to displace an equal number of coal-fired facilities; a wedge requires an additional amount of natural gas equal to that used for all purposes today.

If we look to capture carbon from power stations and pump it underground, we would need to do this for some 800 gigawatts of coal-fired power stations or 1,600 gigawatts of natural gas electric plants. A wedge will require injecting a volume of carbon-dioxide (CO₂) equal to the amount of oil extracted every year. There are currently three storage projects that each inject one million tonnes of CO₂ per year - by 2055 we'd need 3,500.

Another wedge could be achieved by tripling the world's nuclear electricity capacity or building 600 high-temperature plants to produce hydrogen. We currently have none. The rate of installation required for a wedge from nuclear electricity is equal to the global rate of nuclear expansion between 1975 and 1990. And the phasing out of nuclear electric power would create the need for another half wedge of emissions cuts.

What about wind? One wedge would mean installing two million windmills to replace coal-based electricity, or four million windmills to produce hydrogen fuel to replace gasoline. A wedge would require about 30 million hectares of land covered by wind farms to increase current capacity by a factor of 50, equivalent to 8.5 per cent annual growth. And solar? A wedge of solar electricity would mean increasing current capacity 700 times, or an annual growth rate of 14.3 per cent.

Biofuels is another way we can find a wedge. If we scale up current global ethanol production by 50 times, we'd have a wedge. Using current practices, one wedge requires planting an area the size of India with biofuel crops by 2055 - that's an area equivalent to one-sixth of world's crop land.

The intention of this list is not to give the impression that the task is overwhelming. On the contrary, all these technologies are available today and can be used to reduce our greenhouse emissions. But what it does show is that one single technology will not provide the solution. We need all of them!

The Sun doesn't shine all the time and the wind doesn't always blow. But that doesn't matter. Our electricity grid will have many different sources of energy being fed into it - and in the case of wind and solar these will be placed all around Australia. When it isn't windy or sunny in one location, it is more than likely to be so in another.

The experience in Europe shows that an electricity grid can quite easily cope with some 20 per cent of its electricity coming from wind. But as we can see from the scale of the task outlined above, getting that 20 per cent - and the other 80 - will be difficult. We will need to use all of the technologies available to solve the problem.

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