(The author is a Reuters market analyst. The views expressed are his own.)
By Gerard Wynn
LONDON, April 25 (Reuters) - More data on the greenhouse gas emissions impact of shale oil and gas is needed to pinpoint their climate impact, something which recalls a controversy over Canadian tar sands where opposing lobby groups were said to have cherry-picked data.
Shale gas has revolutionised the U.S. energy industry, pressuring prices while tight (also called shale) oil production is on a steep upward curve. Each was enabled by advances in horizontal drilling technology.
The greenhouse gas (GHG) impact of shale gas is uncertain but likely not much more than conventional gas, but next to zero research has been made into emissions from tight oil.
The uncertainty problem rekindles the tar sands debate, where green and industry lobbies have squared off by exploiting uncertainty in emissions numbers, confusing assumptions, tar sands projects (some are cleaner running) and an error margin of about 5 percentage points.
Doubt is multiplied for shale gas and oil -- newer technologies with an even less settled academic view.
Critical questions include: how do the direct GHG emissions compare with conventional fossil fuels; will they displace coal CO2 emissions or add to them; and how pressing is the wider climate problem?
The context for the climate problem is that humankind can only emit a certain total of GHGs and stay within an international target limiting global warming to no more than 2 degrees Celsius.
A letter published in the journal Nature in 2009 calculated that "emissions budget" to be 1,440 billion tonnes of CO2 from 2000-2050. By 2010, the available budget had already shrunk to about 1,100 billion tonnes.
Global CO2 emissions in 2010 were 36.5 billion tonnes, including deforestation plus burning fossil fuels, according to data from the energy company BP and the Global Carbon Project research group.
Continuing such levels would swallow up the remaining budget by 2040, when global CO2 emissions would have to stop altogether.
That's hardly practicable, implying one of two options: miss the warming target or cut emissions sooner.
It follows that environmental regulation will probably get tougher, and that shale fuels should be at least no more CO2-emitting than conventional fossil fuels.
The trouble with natural gas is that its core ingredient is methane, a greenhouse gas (GHG) with a much stronger global warming potential than CO2.
In the case of shale gas extraction, methane can leak both from ("flowback") fluids used to blast gas out of the fractured shale rock, or from drilling of wells - the first process does not apply to conventional natural gas.
The range of shale gas GHG emissions is defined by a handful of studies.
Near the top end, Cornell University scientists last year estimated that methane emissions were at least a third higher than for conventional gas, making shale gas comparable to coal, widely regarded as the most climate-unfriendly fossil fuel.
That followed a U.S. Environmental Protection Agency (EPA) study which concluded that methane leaks may be far higher than with conventional gas. Earlier this year the Cornell authors recently stood by their research.
Nevertheless both have been criticised.
For example, the consultants IHS CERA said that such high levels of (flammable) methane emissions would be impossible in practice, simply as a fire hazard.
It said the EPA and Cornell studies misunderstood industry practice (for example, exaggerating methane venting into the atmosphere), and used a simplistic and inappropriate averaging of data.
Regarding North America's burgeoning tight oil, there is even less to go on - with all but zero CO2 research, experts say.
Shale oil is on track to be a significant part of U.S. crude production, presently nearing a tenth of domestic output.
Possible CO2 problems may include gas flaring, but probably pale against the emissions impact of pumping steam into sand to extract tar crude in Canada.
The answer to resolving the CO2 impacts is more data, and putting in place often simple response measures, for example in the case of shale gas containing methane emissions by housing rather than exposing flowback water.
The IHS CERA report applauded EPA regulatory proposals if these codified best practice and led to wider emissions measurement.
Without more data, doubts will grow and industry lag best practice, inviting misunderstanding and protest. (Editing by Keiron Henderson)