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More than 80 per cent of the world’s known coal
reserves need to stay in the ground to avoid dangerous climate
change, according to new research.
Thirty per cent of known oil and 50 per cent of gas reserves are
unburnable and drilling in the Arctic is out of the question if
we’re to stay below two degrees, the new research notes.

That vast amounts of fossil fuels must go unused if
we’re to keep warming in check isn’t a new idea. What’s novel
about today’s
is that it pinpoints how much fuel is unburnable in
specific regions of the world, from Canadian tar sands to the
oil-rich Middle East.

Unburnable carbon

In its most recent report, the Intergovernmental Panel
on Climate Change (IPCC) calculated
how much carbon we can emit
and still keep a
decent chance of limiting warming to two degrees above
pre-industrial levels. This is known as a
carbon budget
. Two degrees is the
point beyond which climate change
risks become unacceptably high.

As of 2010, we could release a maximum of about
1000 billion
more tonnes of carbon dioxide and still
have a 50:50 chance of staying below two degrees, according to

Today’s paper compares this allowable carbon
budget with scientists’ best estimate of how much oil, gas and coal
exist worldwide in economically recoverable form, known as

Were we to burn all the world’s known oil, gas
and coal reserves, the greenhouse gases released would blow the
budget for two degrees three times over, the paper

Regional breakdown

The implication is that any fossil fuels that
would take us over-budget will have to be left in the ground.
Globally, this equates to 88 per cent of the world’s known coal
reserves, 52 per cent of gas and 35 per cent of oil, according to
the new research.

The University College London team used a
complex energy system model to investigate the fraction of
“unburnable” fossil fuel reserves in 11 specific regions

The results suggest the Middle East holds half
of total global unburnable oil and gas reserves, with more than 260
billion barrels of oil and nearly 50 trillion cubic metres of gas
needing to remain untouched if we’re to stay within budget. This
“unburnable” fraction equates to two thirds of the region’s gas and
38 per cent of oil reserves. Russia accounts for another third of
the world’s total unburnable gas, as the map below

How much oil, gas and coal will we have to leave
in the ground to stay under 2 degrees of warming.

Credit: Rosamund Pearce, Carbon Brief derived from McGlade et
al. (2014)

Coal, the most polluting of the three types of fossil
fuel, faces the most restrictive limits. Russia and the US could
burn just five per cent or less of their coal reserves if we’re to
stay below two degrees. In Europe, keeping within budget means 89
per cent of known coal and 21 per cent of oil is unburnable.

Gas plays an important role in replacing coal in
the electrical and industrial sectors in a two-degree scenario, the
paper notes. According to the analysis, about 94 percent of
Europe’s gas reserves are still burnable in a two degree world.
That’s compared to about 30 per cent of the Middle Eastern gas
reserves, which are much larger.

It’s also worth noting the new model estimates
the most cost-effective way to stay below the two degree budget,
based on the production costs of the various types of fuel in each

So it’s not the only way forward and is by no
means a prescriptive solution, lead author Dr Christophe McGlade
tells Carbon Brief. Instead, he said the research could feed into
negotiations as a starting point for wider conversations about
historical responsibility, equity and potential compensation

Unconventional gas

It’s worth noting, the numbers above relate to
known “reserves”. These are fossil fuels that have already been
discovered and have a high probability of being recovered under
current economic conditions. This is different from fossil fuel
“resources”. These are all the fossil fuels thought to exist which
are potentially recoverable irrespective of economic

Today’s research suggests 25 per cent of
Europe’s unconventional gas resources could feasibly be exploited
while still remaining below two degrees. This includes shale gas,
tight gas and coal-bed methane. How much of this is economically
viable to recover remains to be seen, however.

Should that change in the future, balancing the
two degree budget would probably require that more readily
available reserves elsewhere would have to go unburned, McGlade
tells Carbon Brief.

Turning to the global picture, meeting our
two-degree commitment in a cost-effective way means leaving all
unconventional oil and 82 per cent of unconventional gas resources
in the ground, according to the model. That means Canada’s tar
sands and the 100 billion barrels of oil estimated to exist in the
Arctic would need to go untouched, the paper explains.

Capturing carbon

According to today’s research,
technology to
greenhouse gas emissions before they
reach the atmosphere would only have a limited impact
on the proportion of fossil fuels that can be burned. Carbon
Capture and Storage (CCS) would allow just six per cent more of the
world’s known coal reserves to be burned, with an even lower figure
for oil and gas. The paper explains:

“Because of the expense
of CCS, its relatively late date of introduction (2025), and the
assumed maximum rate at which it can be built, CCS has a relatively
modest effect on the overall levels of fossil fuel that can be
produced before 2050 in a two-degree scenario”.

The new research paints a stark picture of the
compromises in fuel use necessary in a climate-constrained world.
The researchers say it raises the question of how we divvy up the
winners and losers, and that’s one we should all now be asking of
our policymakers.

McGlade, C & Ekins, P. (2015) The geographical
distribution of fossil fuels unused when limiting global warming to
2C. Nature,