Energy: Looking for the free ecological lunch
A leak from a gas rig in the middle of the North Sea is once again throwing up questions about the relative safety of different forms of energy.
The story has so far been told from the human point of view, and why not - clearly it's very much a safety issue when you have inflammable gas percolating up through the sea, and some of the same gas on fire as it emerges from a stack on top of the Elgin rig.
With all the workers now off the rig, scientists are starting to look at the ecological effect of having so much gas bubbling into the water column.
They're the same type of questions that were asked in the aftermath of the Deepwater Horizon disaster in the Gulf of Mexico, and when the stricken Fukushima nuclear power station began flushing radioactive elements into the oceans just over a year ago.
Elgin field gas is mainly methane - the stuff we burn in our cookers - but it also contains related substances: propane and butane, as well as others such as hydrogen sulphide.
A "sheen" of condensate from this is apparently lying on the sea surface, containing up to about 20 tonnes of material.
What's of more concern ecologically is what impact the gases may have had as they bubbled up through the water, in quantities that have not yet been evaluated.
The UK Department of Energy and Climate Change (Decc) said "there is no indication of a risk of significant pollution to the environment".
Not all scientists are as sanguine.
"Methane and hydrogen sulphide, when dissolved in water, are highly toxic to most higher forms of marine life," said Christoph Gertler, who studies bioremediation at Bangor University.
"It can be assumed that fish will avoid the area immediately affected by the spill, but in any case the effects of hydrogen sulphide and methane are more acute than chronic, and there should be no accumulation in the food chain."
Perhaps no long-term impact, then, but a possible short-term shock.
We're nearly two years on from the Deepwater Horizon disaster, which saw oil (along with gases such as methane) streaming into the Gulf of Mexico at rates of about 40,000 barrels a day for months. The impact on the coastline was starkly seen through oiled pelicans, dead seagrasses, and slicks stretching for miles.
But underwater was a different matter. Only now is it becoming clear.
Last week the US National Oceanic and Atmospheric Administration (Noaa) said: "Since February 2010, more than 675 dolphins have stranded in the northern Gulf of Mexico - a much higher rate than the usual average of 74 dolphins per year."
Further along the coast, away from the peak oil plume, stranding rates are normal.
Noaa has declared this an Unusual Mortality Event and is investigating the causes of death. The main clue so far is that some of the dolphins show significant imbalances in hormone levels.
In one sense this is really surprising. Dolphins are among the most intelligent marine animals, highly mobile and adaptable.
So why didn't they take evasive action? There are several possible explanations.
You might also ask what the impacts are likely to be on other less intelligent, less mobile and less adaptable creatures.
The gulf is a spawning ground for fish including bluefin tuna; before too long we may discover whether Deepwater Horizon affected spawning during the 2010 Spring.
Half a world away, meanwhile, the impacts of the Fukushima outflow on marine life are equally hard to measure, but appear so far to be negligible.
In October, a US-Japanese research team published a scientific paper concluding that although much more research remained to be done, there appeared to be "minimal impact on marine biota or humans due to direct exposure [to radioactive nuclides] in surrounding ocean waters".
And just last month, one of the scientists involved, Ken Buesseler, told a US scientific meeting that although elements from Fukushima could be detected in organisms 600km from the stricken power station, their radioactivity was dwarfed by the natural radioactivity in seawater.
Bans on fishing and on eating fish remain in place, and Japan is setting tighter limits for acceptable levels of radioactive contamination in seafood products.
But overall, Fukushima - the largest ever release of radioactive material to the oceans apart from nuclear bomb explosions - has produced no impact on marine life that has yet been discerned.
(And plans to build a wind farm near Fukushima to replace lost electricity generation capacity and regional employment are under attack from fishermen, who fear the turbine towers will damage their generally productive fishing grounds.)
Meanwhile, marine mammals in the Arctic carry mercury levels high enough that they make toxic eating for indigenous peoples who have traditionally consumed them. The main anthropogenic source of mercury is coal burning, the heavy metal sent up power station chimneys and carried polewards on the wind.
We all need energy of some kind - and the global demand is set to increase as both the human population and our consumption grow.
So ecological footprint is a key factor in determining which energy sources to use - which is why we need to carefully dissect the impact of accidents such as Elgin, Deepwater Horizon and Fukushima.