Summit misses the 'C-word'
Some fascinating threads on energy and climate change are swirling around the heads of Presidents Barack Obama and Hu Jintao as the two leaders convene in Washington DC.
China's energy direction is assured - but is the US's?
The "C-word" isn't being mentioned in despatches at all - but the E-word is, with a number of bilateral business relationships strengthened on the eve of Mr Hu's appearance at the White House.
The two giant nations are facing somewhat different questions on energy.
And as faraway the two leading emitters of greenhouse gases, the choices they make are obviously highly significant for the world's future climate.
US energy demands are roughly stable.
But it wants to be more independent of external suppliers, and the Obama administration wants to use less energy overall; so there are decisions to be taken on which options to pursue.
China, on the other hand, needs more energy every year and is pursuing all options, with consumption of fossil fuels and use of renewables expanding rapidly, and an ongoing programme of nuclear reactors.
For the US, China becomes a competitor in consuming oil and gas reserves, and potentially a competitor in the production of wind turbines and solar panels.
That's one factor in US thinking, as the various strands of government struggle to plot an energy future.
There are others. Cost is a big one, always; and here, fossil fuels and nuclear reactors still hold the whip hand, at least according to a recent analysis from the International Energy Agency (EIA).
The IEA found nuclear and coal were generally cheaper than wind
Security of supply considerations point to renewables, nuclear and coal - and to full exploitation of North American tar sands and shale gas.
On the other hand, if world governments do decide in coming years that they're seriously concerned enough about climate change to initiate a full-scale transition to renewables-based generation, a massive investment in renewables manufacturing and deployment now could prove to be a good long-term move.
Otherwise, China, India, and the EU will be well set to dominate the market.
Snubbed by the Senate over comprehensive climate legislation, and chary of his chances of persuading a more climate-sceptical public, Mr Obama and allies such as John Kerry now couch prospective regulation in terms of energy security and green jobs.
The problem is, those two factors can also point to shale gas and "clean" coal - which, as campaigners often point out, does not exist yet.
On the other side of the Atlantic, Greenpeace and renewables consultancy Energynautics have just published a report showing that doing a bit of everything is not necessarily a good option.
In particular, requirements for an electricity grid are very different if you plan for relatively few big generators delivering baseload power or lots of smaller ones delivering more intermittent or periodic power.
In Europe, Greenpeace says:
"At times of peak production, renewables delivering clean and virtually free energy are already being muscled off the grid to allow nuclear and coal plants to continue running.
"This is because wind and solar power is variable, while nuclear and coal plants are constant but inflexible..."
Choices grid companies make are also, however, determined by cost... which brings us back to the EIA report.
It's been an unwritten assumption down the years by many in the climate field that climate priorities will decide energy pathways.
The Cancun agreement acknowledges that time to curb climate change is running out
Follow the science of climate change, the thought goes, and that will mandate how governments and businesses proceed - often with financial levers such as carbon pricing applied.
However, looking at the current state of global climate policy, it's possible to argue that the converse is true - energy concerns are the drivers of climate policy.
At its most obvious, it's why the Gulf states typically oppose tough emission curbs.
But it's more subtle as well.
China has set the targets it has - and remember, all nations' targets are now essentially unilateral - because it can meet them with an energy policy mix that it considers achievable and in the national interest, matching current and future economic priorities with concerns over climate impacts.
The US, with its very different system of government, is feeling all the pressures, but not as yet coming up with any semblance of a defined response.
Attempts to impose tougher regulations on emissions are being met with legal challenges and political opposition, and the likely success of those attempts is hard to gauge.
In the meantime, the agreement hammered out at the UN climate summit in Mexico [pdf link] late last year makes clear that governments do not have much time to waste in cutting emissions:
"Parties should co-operate in achieving the peaking of global and national greenhouse gas emissions as soon as possible... [the UNFCCC] further agrees to work towards identifying a timeframe for global peaking of greenhouse gas emissions based on the best available scientific knowledge and equitable access to sustainable development, and to consider it at its seventeenth session [ie this year]."
Given the urgency inherent in that statement and the pivotal position of the US-China rivalry in climate negotiations, you might conclude it's strange that the two leaders aren't talking about climate change this week.
But with one country having made its energy choices, and the other struggling to do so against the backdrop of conflicting pressures - maybe it's not so strange after all.