But the goal is to meet those targets... not to do so without a given technology.

The UK is sensibly going with as many clean options as possible.

From Presidential Science Advisor John Holdren:

The renewable option: Is it real?
SUNLIGHT:
100,000 TW reaches Earth’s surface (100,000 TWy/year = 3.15 million EJ/yr), 30% on land.
Thus 1% of the land area receives 300 TWy/yr, so converting this to usable forms at 10% efficiency would yield 30 TWy/yr, about twice civilization’s rate of energy use in 2004.

WIND:
Solar energy flowing into the wind is ~2,000 TW.
Wind power estimated to be harvestable from windy sites covering 2% of Earth’s land surface is about twice world electricity generation in 2004.

BIOMASS: Solar energy is stored by photosynthesis on land at a rate of about 60 TW.
Energy crops at twice the average terrestrial photosynthetic yield would give 12 TW from 10% of land area (equal to what’s now used for agriculture). Converted to liquid biofuels at 50% efficiency, this would be 6 TWy/yr, more than world oil use in 2004.

Renewable energy potential is immense. Questions are what it will cost & how much society wants to pay for environmental & security advantages.


The nuclear option: size of the challenges

If world electricity demand grows 2%/year until 2050 and nuclear share of electricity supply is to rise from 1/6 to 1/3:
– nuclear capacity would have to grow from 350 GWe in 2000 to 1700 GWe in 2050;
– thismeans1,700reactorsof1,000MWe each.

If these were light-water reactors on the once-through fuel cycle:
– enrichment of their fuel will require ~250 million Separative Work Units (SWU);
– diversion of 0.1% of this enrichment to production of HEU from natural uranium would make ~20 gun-type or ~80 implosion-type bombs.

If half the reactors were recycling their plutonium...
– the associated flow of separated, directly weapon- usable plutonium would be 170,000 kg per year;
– diversion of 0.1% of this quantity would make ~30 implosion-type bombs.

Spent-fuel production in the once-through case would be:
– 34,000 tonnes/yr, a Yucca Mountain every two years.

Conclusion: Expanding nuclear enough to take a modest bite out of the climate problem is conceivable, but doing so will depend on greatly increased seriousness in addressing the waste-management & proliferation challenges.

So few posts in recent months and you can't be bothered to come up with something original?

Your reply does not support the title. It says (where it's responsive at all) that renewables are an option- not that they are necessary (or even preferred).

Also from John Holdren:

Dr. HOLDREN: Well, I think, first of all, yes, we should be investing in nuclear energy. We should be investing in approaches to addressing the difficulties that have prevented us from expanding nuclear energy to a greater extent up until now. We should be doing research that is addressed at making nuclear energy more cost-effective. We should be doing research to address the problem of how we manage the radioactive waste. We should be doing more research to reduce the linkages between nuclear energy and the proliferation of nuclear weapons.I do think that if we could get an expanded contribution from nuclear energy, it would be a tremendous help in ad-dressing the climate-change challenge, which is almost without question the toughest part of the energy challenges we face.

In addition, going back to the previous point, if we did have plug-in hybrid vehicles, you could finally have nuclear energy, as well as renewable forms of electricity generation, making a contribution to motor-vehicle energy consumption, and that would be terrific.

I was told by the OP that a carbon tax wasn't necessary.

The crux of the matter is that the policy for implementing a carbon tax lacks the necessary political window of opportunity.

In the face of that reality, the same goal is achievable by policies designed to lower the real cost of renewable energy technologies - an approach that is now yielding significant results.

They're not paying their fair share. This is a comment about the tax breaks they get, not necessarily about a tax on carbon in general. Ending their tax breaks is viable and possible, but not with the current Congress. Regardless I do not see the markets making fossil fuels go away any time soon, in fact, we're ramping up production, not lowering it, even with renewables being built out like crazy.

To stop the burning of fossil fuels (civilization's primary source of energy) would require a 180 degree inversion of the way the world actually works. It would require a complete negation of the principles that govern the evolution of all self-organizing complex systems, from plant and animal ecosystems all the way up to human civilization itself.

It ain't happening, folks.

Any new power sources the world brings on line will come as additions to the consumption of fossil fuel, not as replacements. This should be obvious by now, especially if one takes a global view. But it's not, I guess.

GG: "To stop the burning of fossil fuels (civilization's primary source of energy) would require a 180 degree inversion of the way the world actually works."

Not at all, it would be an inversion of the way you erroneously believe the world works.

GG: "Any new power sources the world brings on line will come as additions to the consumption of fossil fuel, not as replacements."

Bullpuckey. There is simply no evidence to support this contention. We routinely leave unexploited energy resources lying fallow because of the availability of higher quality energy resources.

How do you define quality, and where does FF fit on that scale?

We may leave some energy sources lying fallow (but I can't recall any - can you name one?). I don't think we leave high-quality energy sources lying fallow. But we have never stopped using a high quality source while a new one is being developed. So far no renewables - or nuclear power for that matter - have led to any decrease in the use of FF. The only condition under which they could do that would be if the switch-over actually improved the power performance of civilization. Given how entrenched fossil fuels are, that seems like a condition that will not be met before global warming makes the planet a very uncomfortable place indeed.

This is a piece I just put up on another site: