Critics fear spills and say carbon emissions from refining the tar sands will "turbocharge global warming". Nine Nobel Laureates, including Archbishop Desmond Tutu and the Dalai Lama, have weighed in, saying the pipeline will fuel climate change and "endanger the entire planet".
Elsewhere, Obama is accused of reaching into George W. Bush's pro-polluter playbook as he gives Shell tentative approval to drill off the coast of the Arctic National Wildlife Refuge - a goal denied Bush - and of siding with the American Petroleum Institute, calculating that renewed exploitation of fossil fuels will increase jobs and relax the foreign stranglehold on America's energy supply (in this calculation at least, Canada doesn't count as foreign).
In the green camp, there is a despairing sense of clean tech opportunities missed.
"When Obama won the White House the oil business saw a threat and they rearmed," says Kert Davies, research director with Greenpeace USA. "And they sent hordes of lobbyists to Washington, and doubled down on ... campaigns to keep things the way they are. The President said some harsh things about the industry after the Deepwater oil spill.
"But in the end all US policy has bent to the oil industry. And we don't see any change."
Economic woes have also stalled investment in renewable energy alternatives.
But while frontier oil exploration and record coal sales remain the in-your-face energy reality, three inexorable, linked factors are driving deeper change.
The first is the huge energy demand caused by runaway population growth - by 2050, humankind is expected to number 9 billion, compared with 1.6 billion in 1900 - and the rise of industrial titans such as India, China and Brazil.
The second is "peak oil" - the moment when oil production reaches its highest point, then starts to decline. Whether this has occurred is contentious. It is hard to know the world's fossil fuel reserves, but they are finite.
Last year's annual report from the International Energy Agency (IEA) forecast global oil production would reach 96 million barrels per day (mb/d) in 2035 (in June it was 88.7 mb/d), driven by natural gas and "unconventional oil" such as tar sands, as conventional crude levels out.
Extracting oil would become more expensive and leave a bigger legacy of polluting carbon. And energy demand would soar 36 per cent by 2035, with most of that extra demand coming from non-OECD nations, led by China.
Oil drives transport, but electricity generation is the key to record coal consumption. Nuclear power, meanwhile, faces an uncertain future after the meltdown at Fukushima: Germany will close its reactors by 2022 and this month's explosion at a French nuclear waste site fuelled fears about safety, radioactive waste and CO2 emissions from uranium processing.
Meanwhile, infinitely sustainable renewables - solar, wind, hydro, geothermal, biofuel and ocean power - produced 16 per cent of world energy last year. The IEA forecasts that renewable use will triple between 2008 and 2035.
The third factor is climate change. When the OECD announced five "global shocks" likely to destabilise the world economy, climate change wasn't mentioned.
But money men at the sharp end, such as those in the reinsurance business, routinely factor in findings agreed by the United Nations Intergovernmental Panel on Climate Change.
However, if the past is any clue, switching energy sources will be a protracted, stop-start affair during which competing realities co-exist.
Sail didn't give way to steam overnight, just as steam didn't surrender to oil in an instant. Big Oil and renewables may co-exist for decades, given the complex challenge of rejigging vital infrastructure - transport, power generation and the like - in developed societies addicted to the old fossil fuel order.
But while making the transition is expensive, delaying may be more so. Studies suggest that choosing renewables increases jobs and wealth by more than expanding sunset industries. At the same time, clean energy costs are coming down, as oil costs climb.
According to a Greenpeace International report released in June, wind and solar energy installations have grown faster since the 1990s than any other energy plant technology, accounting for 26 per cent of new power plants added to electricity grids worldwide in the past decade.
A 2010 Pew Environmental Trust report, Who's Winning the CleanTech Energy Race?, says US$162 billion ($197 billion) was spent on clean-tech energy projects worldwide in 2009. And the US Political Economy Research Institute's 2008 Green Recovery report found that US$100 billion would create two million jobs in two years, quadruple the number of jobs this sum would produce in the oil business.
"There is a strong US environmental and labour lobby for a green transition," says Robert Pollin, co-author of the PERI report. "But it hasn't coalesced, so inertia and entrenched interests are prevailing."
Pollin, who believes renewables will drive energy needs by 2100 "if we make it", says funding has slowed while vested interests and US conservatives slam green technology as a "job killer".
But despite recession and other obstacles, renewables are moving on to the energy stage. Spain has now surpassed the US in solar power production, generating energy equivalent to a nuclear power plant. Germany has one of Europe's biggest solar programmes. Wind power is surging ahead in Mexico and Brazil. Indonesia is exploring geothermal resources. And China is emerging as the nation to beat in clean power generation.
An Intergovernmental Panel on Climate Change report in May found that renewables drove 140 gigawatts of the 300GW of "new" electricity generated worldwide between 2008 and 2009. Wind power grew by 30 per cent, hydro 3 per cent, geothermal 4 per cent, solar water heating 20 per cent, ethanol and biodiesel by 10 per cent and 9 per cent each. Solar photovoltaics connected to the grid grew over 50 per cent. And developing nations hosted over 50 per cent of renewables.
Despite some doom and gloom in the US and European clean-tech markets, Alex Klein, a renewables strategist with US consultancy IHS Cambridge Energy Research Associates, says "we saw rapid growth in 2010 from renewables capacity investment. We're seeing an increase in the global push towards renewables in Europe and North America.
"Renewable companies are looking for areas of growth. We're seeing increased activity in Latin America. And certainly in Asia. A majority of command renewable growth is going to come from emerging economies."
It is a world view that distinguishes between short-view investment - using fossil fuels to feed existing infrastructure - and a longer-term vision based on peak oil, rising energy demand and climate change.
The 2006 Stern Review on the economics of climate change argued that tackling climate change now by switching to renewables would cost about 2 per cent of global GNP based on 2008 estimates, but this would be much less than the cost of ignoring climate change.
"We add US$1 trillion to the cost [of tackling global warming] with every year of delay," Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change, said in June.
The IEA said this annual sum was good to 2030 if we want to limit temperature rise to 2C, a goal that requires "rapid decarbonisation of global energy". In this scenario, low-carbon technologies must account for 75 per cent of global power generation by 2035, a four-fold increase.
It won't happen with fossil fuels, despite talk of carbon sequestration and hugely expensive geo-engineering visions. Existing clean technology, from electric or hybrid cars to renewable power generation, is far more feasible.
The big question is how long a move to renewable energy will take. "The share of the global energy that comes from renewables is on an upward trajectory," says Klein. "But it's on an upward trajectory from a very small base. Let's say 5 per cent of the global mix.
"Maybe in the next 10 to 15 years we'll get to 10 per cent and see a doubling of the clean energy contribution to the power generation mix."
Several factors could speed things up for renewables. More investment is crucial. Levelling the subsidy playing field would make renewables more competitive - fossil fuels got US$312 billion in 2009, while renewables got US$57 billion, according to IEA figures - and rising oil prices may boost renewables in transport and heating.
"Renewables are entering the mainstream, but long-term support is needed to boost their competitiveness," says the IEA.
A global carbon agreement would also help. This is impossible in the near term without a deal between China and the US, although Klein suggests European nations might reduce carbon emissions in a strategic bid to capture the renewables industry.
China, which is on a path to becoming the world's leading renewables power, has also made noises in this direction. The 12th Five-Year Plan for 2011-2015 includes a carbon cap, a regional carbon trading scheme, pollution controls and renewables. Crucially, it also foresees a low-carbon economy as an alternative to GNP for measuring economic performance.
China exemplifies two parallel energy realities: one short-term, the other long-term. On the one hand, it burns prodigious amounts of coal, oil and gas (Canada's planned Pacific pipeline has China in mind as a customer) and is committed to nuclear power. On the other hand, China sees using such resources as a pragmatic move, as it makes the transition to clean technology.
Unlike the US, Big Oil is not in the driver's seat. Economies of scale drive down clean technology costs, such as the price of gearboxes and turbines for wind power, or solar panels (seven of the world's 10 major solar manufacturers are Chinese), benefiting consumers everywhere who want to switch to renewables.
Writing on the Huffington Post website, Stephanie Praus, who co-ordinates the US Climate Leadership Group, says it is in America's self-interest to fund clean tech. "Climate finance reduces the risk of investing in clean technologies and will thereby increase its economic returns over time, leading to a positive feedback loop of more investment in clean technologies and ever more demand for US products."
Klein sees room for hope. Tighter US emissions rules will take "30 to 50GW of coal [power plants] off-line in the next decade". Similar pressure will apply elsewhere, while developing nations will avoid coal and focus on renewables.
"The long-term drivers are still in place for a decarbonisation of the power generation market."
Don't expect encouragement from the oil industry. Saudi Arabia has already floated the idea that it should be compensated for revenue losses if its oil exports - US$300 billion last year - shrink because of declining demand. But the status quo, with fossil fuel industries uncoupled from the cost of carbon emissions, looks well overdue for a reality check.
