former manager of global research
and special projects,
Physics harbour a frightening punch line for the story of climate change: even though
the consequences of global warming persist for the very long term, the time available in
which to avoid them is very short. Thus a delay — of even a decade — in reducing CO2
emissions will lock in large-scale, irreversible change. It also increases the risk that the
whole climate system will spin out of control.
This message may be alarming, but this is not alarmism. It’s physics. And the earth’s
climate physics have serious implications for political action and technological innovation
in the coming decade.
The story has five parts:
1. Stabilizing CO2 at any concentration requires very low emissions
For hundreds of thousands of years prior to the industrial era, such natural processes
as plant growth, animal respiration, and soil erosion kept atmospheric concentrations
of CO2 in balance. But burning fossil fuels has introduced as much carbon in the past
50 years as had been sequestered over millions of years, thus upsetting the natural balance.
Atmospheric CO2 concentrations are now nearly double their pre-industrial level.
Once emitted, CO2 remains in the atmosphere for centuries, or even millennia. Every
ton introduced is therefore cumulative, and the resulting increases in concentration
will persist in the atmosphere for thousands of years — even if emissions are reduced
tomorrow. So stabilizing CO2 concentrations at any level ultimately requires very
Carbon “sinks” are disappearing
Until recently, natural “sinks,” primarily oceans and plants, absorbed much of the carbon
dioxide dumped in the atmosphere. About a quarter of the CO2 released each year is
absorbed by the oceans (making them more acidic) and roughly another quarter by
plants. These natural safety valves have masked almost half the impact of our emissions.
But as the world emits more CO2, these sinks are becoming saturated. Although oceans
continue to absorb a greater volume of CO2, they are becoming less efficient sinks, able
to take in a shrinking per centage of emissions. This means that even if emissions remain
constant, the growth rate of CO2 concentrations in the atmosphere will soon jump, as
this physical forgiveness gives out. Then we will be in deep trouble.
Many impacts of climate change are irreversible
Due to time lags inherent in Earth’s physical systems, climate changes caused by CO2
emissions will persist — and even grow — for centuries, even after emissions are halted.
We are already seeing some effects of increased greenhouse gas levels, but have yet to
witness the full impact of the current atmospheric accumulation. This is because the
earth’s surface temperature does not react instantaneously to rising carbon dioxide
levels, largely due to the oceans’ tremendous capacity to absorb heat.
The changes can have serious consequences: permanently altered ecosystems, extinctions,
and significantly reduced crop yields. Projections suggest we will lose 18 to 35 per
cent of all species due to climate-forced extinctions. Other system changes — from
ocean circulation to ice melt — are irreversible for thousands of years, at least.
The system can spin out of control
The earth’s reactions to changing CO2 concentrations — altered global weather patterns,
ocean temperature and acidity, and ecosystems, to name a few — are not linear. They
can snowball, eliminating our ability to influence the outcome.
As warmer temperatures melt sea ice and reduce snow cover in the Arctic, for example,
the darker surfaces of the newly exposed ocean and land absorb more heat from the
sun than the light-colored ice and snow that previously covered them. This accelerates
warming, further reducing snow cover. And the thawing permafrost in the Arctic Ocean
is starting to leak large amounts of methane, a powerful greenhouse gas, into the atmosphere.
Release of even a fraction of the methane stored in the seafloor could trigger
abrupt climate warming — and there is no practical way to contain it. If we are to reduce the risk of such runaway feedback
loops, we must rapidly cut
greenhouse gas emissions.
Acting now saves money
Most energy-consuming assets
— such as buildings, vehicles,
factories, and power plants —
have long lives that lock in their
patterns of energy use for decades.
The cheapest way to reduce CO2
emissions is to ensure that new
capital equipment is very efficient
and powered by low-carbon
sources. It will be enormously
costly if the world misses this
opportunity, builds inefficient
infrastructure, and then has to renovate it. Transforming infrastructure at the same pace
as natural capital stock turnover is cheap; forcing such a turnover is very expensive.
Nations must put energy efficiency policies — such as fuel efficiency standards and
building codes — in place now, not later. And governments must invest substantially now
in research and development to drive down the cost of clean technologies and convert
our energy supplies to near-zero sources. If we delay, the cost of reducing emissions sufficiently
will shock the global economy.
Given carbon dioxide’s persistence in the atmosphere, it is useful to think of emissions
in terms of a CO2 budget, or a maximum volume of cumulative emissions that will allow
atmospheric concentrations to stabilize.
If the world is to limit average global warming to 2° C — a threshold most climate scientists
describe as a dangerous tipping point — it will need to stabilize atmospheric CO2
at about 450 ppm. This corresponds to a total CO2 budget of about 1,000 gigatonnes, or
a trillion metric tons, of emissions for 2000–2050. Yet in just the first five years of this
century, the world used up nearly 20 per cent of this 50-year carbon dioxide budget; at
current rates, the full budget will be depleted in less than two decades.
Addressing climate change is like turning an ocean liner: Changing course takes time,
and no amount of rudder, applied too late, will hit the mark. If the world does not start
to reduce emissions now, it will not reach any meaningful CO2 concentration target.
The longer we wait, the more drastic the cuts — and associated costs — will be. If
we delay action for even a decade, CO2 concentrations are likely to soar right past
450 ppm and unleash dangerous, uncontainable ecological and geophysical responses.
If we instead step up to the challenge, pass strong energy policies and invest aggressively
in clean energy R&D, we have a fighting chance of containing CO2 concentrations at
450 ppm — and averting a climate catastrophe.