According to a 2014 report from the U.N.
Environment Program, the total maximum amount of additional carbon that
can be emitted without raising the average
temperature by more than 2 °C is about
1. 1 trillion metric tons. (In 2014 the world
produced 35. 9 billion metric tons of carbon.) But that is only an estimate.
So how do you formulate international
climate policy given the scientific uncertainties? A number of experts are calling for a self-adjusting policy mechanism
that establishes a simple formula for progressive emissions cuts based on empirical data, rather than limits set years in
advance. By responding to what’s already
happened, rather than what scientists
conclude is likely to happen, such a system would, at least in theory, sidestep the
uncertainty of climate forecasts.
This new approach took form in an
August 2015 paper published in Nature
Climate Change by a group of researchers
headed by Myles Allen, a professor of geo-system science at the University of Oxford,
and Friederike Otto, a lecturer in physical
geography at Oxford and a research fellow
at the Environmental Change Institute.
The paper, titled “Embracing Uncertainty
in Climate Change Policy,” argued that
a flexible, self-correcting system would
be “anti-fragile,” in that “uncertainty and
changes in scientific knowledge make the
policy more successful by allowing for trial
and error at low societal costs.”
Think of the U.S. Federal Reserve
Bank. The Fed doesn’t set interest rates
far into the future by gazing at computer
models of the economy and predicting
GDP growth and inflation two decades
out; it monitors key indicators, reviews
its positions, and adjusts interest rates
accordingly. It has succeeded remarkably
well at keeping inflation in check even as
parts of the economy—such as the mort-
gage lending sector—periodically blow up.
That approach contrasts with what’s
known as the precautionary principle—the
doctrine that policy makers should base
their decisions on avoiding the worst-case
scenario. Precautionary models developed by economists including Martin
Weitzman, of Harvard, dictate that even
if the risks of climate catastrophe are
small, its effects would be so radical that it
should be avoided at almost any cost. The
problem with such an approach is that it
requires politicians to marshal tremendous
resources and take aggressive actions—
such as drastically limiting carbon emissions in poor countries like India—that
may be unrealistic and even harmful.
The system Allen and Otto propose
would respond directly to the amount
of measurable warming attributable
to human activity. The scheme has a
straightforward prescription: the world
must reduce emissions by 10 percent for
every one-tenth of one degree of warming
(beyond the 1 °C mark we have already
effectively reached). As temperatures near
2 °C of warming, emissions ratchet pro-
gressively downward, eventually to near
zero. The system responds to uncertain
outcomes with a built-in self-adjusting
There are advantages to this system,
and some pitfalls. Among the benefits
is that it gives policy makers and gov-
ernments political cover: whether the
observed warming is less than or greater
than predicted, the system responds auto-
matically to the signals. The formula for
those adjustments is agreed to in advance.
“If you’re waiting for science to provide
exact certainty about regional local change
over a multi-decade period, you’re going
to be waiting forever,” says Diffenbaugh.
What the Allen-Otto system doesn’t
do is account for the uncertain effects of
specific amounts of warming—it assumes
nothing about sea-level rise, the frequency of extreme weather events, or
other unpredictable effects of a warmer
planet. “We are framing this system on the
premise that the world has agreed to avoid
more than 2° of warming, independent of
the effects,” says Allen. “It would be hard
to go further than that in an international
system, because you would need to get
agreement on the degree of unacceptability of impacts.”
The larger problem, of course, will be
putting such a system in place. Getting
politicians to commit to voluntary emissions limits decades in advance has taken
many climate summits, over many years.
Getting them to agree to a system that
enforces bigger and bigger cuts based on a
formula is a challenge of a different order.
But as evidence for the consequences of
climate change accumulates in unpredictable ways, this system may be the best way
to make the cuts we need.
Richard Martin is MIT Technology
Review’s energy editor.
No action to limit
cuts that run to 2030.
to ratchet down.
THREE OUTCOMES BASED ON OUR ACTIONS
2000 2020 2040 2060 2080 2100
4. 5 °C
2100 temperature relative to preindustrial levels
3. 5 °C
1. 8 °C