By Eric Vandenbroeck
In a few days world leaders will gather in Paris for a grand conference
on climate change, the 21st such get-together since the United Nations began to
grapple with the issue. A torrent of pronouncements and promises has already
issued forth, from Pope Francis, Xi Jinping, Barack Obama and many others. The
IMF warns that human fortunes will “evaporate like water under a
relentless sun” if climate change is not checked soon.
Barring a global catastrophe or the spectacular failure of almost every
climate model yet devised, though, emissions of greenhouse gases will warm the
world by more than 2°C.
Changes in the atmospheric level of carbon dioxide, the biggest
contributor to global warming, persist for centuries. So it is useful to
imagine that mankind has a fixed carbon budget to burn through. Pierre Friedlingstein, a climatologist at Exeter University,
calculates that if temperature rises are to be kept
below 2°C, the world can probably emit about 3,200 gigatonnes
of carbon dioxide in total. The tally so far is 2,000 gigatonnes.
If annual emissions remain at present levels, the budget will be exhausted in
just 30 years’ time.
Global greenhouse-gas emissions might also hold steady for a while.
Total man-made emissions in 2014 were about the same as in 2013, according to
the International Energy Agency.
The bad news is that even if greenhouse-gas emissions are stabilizing,
they are doing so at an exalted level, and there is little reason to suppose
that the plateau will be followed by a downward slope.
But of course climate change will not be bad for everything and
everyone. Some cold countries will find that their fields can grow more crops;
others will see fish migrate into their waters. With its ocean-moderated
climate, Britain stands out as exceptionally favored. Yet bad effects will
increasingly outnumber benign ones almost everywhere. Some organisms will run
into trouble well before the 2°C limit is breached.
But in the end climate change will have to be tackled more intelligently
and more economically than it has been so far. Renewable energy is crucial.
Contrary to what many claim, though, it is not true that existing solar and
wind technologies could cheaply save the planet while also creating lots of
green jobs if only they were subsidized for just a few more years. Those
renewable power sources have cost consumers dear and mangled energy markets.
Paying for yet more wind turbines and solar panels is less wise than paying for
research into the technologies that will replace them.
Mankind will also have to think much more boldly about how to live under
skies containing high concentrations of greenhouse gases. It will have to
adapt, in part by growing crops that can tolerate heat and extreme weather, in
part by abandoning the worst-affected places. Animals and plants will need
help, including transporting them across national and even continental
boundaries. More research is required on deliberately engineering the Earth’s
atmosphere in order to cool the planet.
It is often said that climate change is an urgent problem. If that were
true, it might be easier to tackle. In fact it is a colossal but slow-moving
problem, spanning generations.
What is known about global
warming - and what remains dark
Greenhouse warming sets off a cascade of effects known as feedback's,
which are harder to measure. On balance, warming begets more warming. Higher
temperatures enable the atmosphere to hold more water vapor. Oceans absorb huge
amounts of carbon dioxide, keeping a lid on climate change, but as they warm
up, their absorption capacity declines. Melting ice produces dark pools of
water that absorb more energy. Partly for this reason, the Arctic is warming
faster than other places.
Inadvertently, though, humans also cool the Earth. Although the overall
effect of deforestation is to warm the planet, replacing trees with crops or
grassland makes the land paler and more reflective. Particles created from sulphur dioxide-the cause of acid rain-reflect lots of
light back into space. China has probably been shielded from higher
temperatures by air pollution, and might heat up quickly if it gets serious
about scrubbing its skies.
The greatest mystery is the effect of human activity on clouds. Because
clouds grow on aerosol particles, more of them are likely to form in a more
polluted atmosphere. Clouds are also affected by temperature changes. But
precisely how is unclear-and this matters, because whereas high clouds tend to
keep the Earth warm, low clouds tend to cool it. Part of the problem in
measuring their effect is that many clouds are small. Climate models tend to
simplify the world by dividing the atmosphere and the oceans into boxes, perhaps
50km by 50km in the horizontal plane, and treating these as pixels in a giant
three-dimensional computer simulation. To capture cloud processes properly
might require climate models with cells just tens of metres
square. No computer in the world could handle that.
Add up all these difficulties; throw in some problems with measuring
temperatures, and you get a lot of uncertainty. The chart on the previous page,
which shows the estimates by the International Panel on Climate Change (IPCC)
of “radiative forcing”-perturbations to the Earth’s energy system from human
and other activities-contains black bars showing 95% confidence ranges. Some of
those bars are long. It is especially hard to be sure of the effect of
aerosols.
If the past is a little hazy, the future is more so. Not only does it
depend on the outcome of physical processes that are inadequately understood.
It also depends on human actions. How many people will be living in 2100? How
rich will they be? Will they make strenuous efforts to cut greenhouse-gas
emissions, do nothing, or something in between?
If mankind makes heroic efforts, the Earth system will remain within
familiar bounds, making predictions easier. If concentrations of greenhouse
gases increase steeply, though, things become highly unpredictable. Passing
irreversible tipping points, such as the collapse of the Greenland ice sheet,
becomes more likely. If nothing were done to avert climate change by 2200, the
IPCC estimates, the world would probably warm by between 3°C and 10°C. That enormous
range is manageable at one end, unimaginable at the other.
Much remains unknown, then. But, equally, much has been settled, it is
just that the settled stuff generates fewer papers and conference panels,
because researchers have moved on. Some possibilities that seemed troubling a
few years ago have been probed and revealed to be less so. It now appears
unlikely, for example, that climate change will lead to the irreversible
collapse of the Gulf Stream. Melting permafrost will emit methane, but not as
much as some once feared.
Even those mysterious clouds are giving up some of their secrets.
Satellite-based radar and laser measurements have enabled scientists to peer
into clouds; small-scale models designed to capture their behavior have been
refined and plugged into global models. It seems increasingly likely that low
cloud cover will diminish as the Earth warms, speeding the process.
Most important, the basic proposition of climate change, the causal
relationship between greenhouse-gas emissions and higher temperatures, has
become almost unassailable. As it happens, the interesting debate about the
global-warming hiatus has a boring coda: 2013 turned out slightly hotter than
1998, and 2014 was roasting, setting a new record. That will not stand for
long.
The biggest single cause of the fossil-fuel boom is China, which is
examined in the next article. But rich Western countries are more culpable than
they think. They have transformed their rural landscapes with wind farms and
pushed up electricity prices for consumers, yet have managed to drive
surprisingly little carbon out of the energy system. The record would look even
worse if Western countries had not simultaneously exported much of their heavy
industry, and thus much of their pollution, to China and other emerging
countries.
Today we large wind farms like for example in Germany. Helped by some
big storms, these turbines produced 41,000 gigawatt-hours of electricity in the
first half of this year, 15% of Germany’s total electricity output. Add
hydro-electric power stations, solar farms and biomass, and the country derived
35% of its electricity from renewable sources. Germany has become a world
leader in green power, but also a warning about what can go wrong.
Wind and sunshine have two big drawbacks as sources of power. First,
they are erratic. The sun shines weakly in winter when it shines at all, and
the wind can drop. On January 20th this year the output from all of Germany’s
solar and wind farms peaked at just over 2.5 gigawatts-a small proportion of
the 77 gigawatts Germany produced that day. A few months later, during a sunny,
windy spell in early June, the combined wind and solar output jumped to 42
gigawatts.
The second problem with wind and solar energy, oddly, is that it is
free. Wind turbines and solar panels are not free, of course. Although the cost
of solar photovoltaic panels has plunged in the past few years, largely because
Germany bought so many, wind and solar farms still tend to produce more
expensive electricity than coal or gas power stations on a “levelised
cost” basis, which includes the expense of building them. But once a wind or
solar farm is up, the marginal cost of its power output is close to zero.
The problem lies with the effect of renewable on energy markets. Because
their power is free at the margin, green-power producers offer it for next to
nothing in wholesale markets (they will go on to make money from subsidies,
known as feed-in tariffs). Nuclear power stations also enter low bids. The
next-lowest bids tend to come from power stations burning lignite coal, a cheap
but especially dirty fuel. They are followed by the power stations burning hard
coal, then the gas-fired power stations. The energy companies start by
accepting the lowest bids. When they have filled the day’s requirements, they
pay all successful bidders the highest price required to clear the market.
Climate-change denial is strikingly rare among China’s political
leaders, some of whom trained as engineers. They understand that their country
is expected to suffer some of the worst consequences of global warming:
northern China, which is increasingly hot and dry, will probably become hotter
and drier still. The politicians are also well aware that their country’s
urbanites are fed up with breathing toxic air.
Nobody quite knows how much coal is burned in China. Misreporting is
common: earlier this year official statistics were amended to suggest that the
country had consumed 14% more coal between 2000 and 2013 than had been thought.
Yet the quantity might now be falling. Consumption seems to have dropped very
slightly between 2013 and 2014. In the first seven months of this year China’s
mines produced 5% less coal than they did during the same period last year. If
this trend were to continue, it would make the government’s pledge to reach
peak greenhouse-gas emissions by 2030 seem unduly modest.
China will remain a heavy polluter. Though steel and cement factories
will probably use less energy in future, ordinary people will doubtless consume
more. As they grow richer, they demand air-conditioning, cars and bigger homes:
in 2012 the average city-dweller inhabited 33 square meters, compared with 25
square meters a decade earlier. Still, the astonishing surge in dirty,
coal-fired energy consumption has probably subsided, thinks Mr
Grubb. It might just be a little hard to see, through the hazy, choking air.
Countries in danger
Few countries of any size are more gravely threatened by climate change
than Bangladesh (which has more than 110m people).
To counter the most spectacular threat to human life, Bangladesh’s
government has built several thousand cyclone shelters, at best, sturdy
buildings sitting atop pillars of reinforced concrete, which in normal times
are often used as schools. One new shelter a few kilometers from Bujbunia could accommodate more than 1,000 people if they
were to press closely together, and might even hold a few hundred cows on the
ground floor. Women and children will rush there if a big cyclone threatens;
men will head for the nearest brick-built mosque.
Farmers are also preparing for storm surges in a humbler way. Scooping
up grayish mud, they build plinths up to a meter high. Leveled and packed down,
these become the floors of their homes; walls and roofs are made of palm
fronds, bamboo and corrugated iron. The aim is to build the plinth higher than
the flood waters will reach, to prevent the family’s food and possessions being
swept away. Even stoves would be destroyed; they are only made of earth.
But to protect themselves against diverse dangers, the farmers of
southern Bangladesh need to make drastic changes. They are doing that by
investing in their children’s education. In a secondary school in the
settlement of Sreefaltola, a class of eighth-graders,
mostly farmers’ children, shout out their plans for the future.
Almost every one of them aspires to be an electrical engineer or a
doctor, or at least to find a job in a nearby city. Not all will succeed; many
will probably stay in farming. But those who make it might be able to move
their parents out of one of the most hazardous places in Asia.
This is not normally what is meant by adaptation to climate change. All
the same, it is the most effective method of adaptation in Bangladesh, says Mr Alam. Some have taken it even
further. In the village of Gobindapur, a grand new
house is being built, two stores high and made of solid brick. It belongs to
Reshma Begum, an imperious woman in a pink sari. Clutching two mobile phones,
she complains that it is becoming increasingly hard to find domestic workers
now that so many young women in the village are running small businesses. Some
of her income comes from a son who works in Malaysia.
Migrations such as these are beginning to show up in official
statistics. Between 2001 and 2011 the population of Barisal division in
southern Bangladesh fell slightly, even as numbers in the country as a whole
went up. Within the district, people moved from the countryside to cities, so
that Barisal’s rural population dropped from 1.96m to 1.81m. By removing people
from the most flood-prone areas, urbanization may be doing as much to preserve
life as any number of cyclone shelters.
A decade ago adaptation was almost taboo in international discussions
about climate change, because it was believed to distract attention from the
task of stopping global warming altogether. Now both are recognized as
important. Rich countries are trying to rustle up $100 billion a year by 2020
to help poor countries cope with climate change, a bribe to keep them coming
back to the climate talks, to be sure, but also a welcome sign of changing
priorities. Even China is chipping in.
It is not yet clear whether the money will be spent on better crops and
fertilizers or on solar panels and other green-energy schemes that will help
poor countries hold down their greenhouse-gas emissions. Britain, which spends
an unusually large share of its budget on foreign aid, suggested in September
that its contribution to the Green Climate Fund would be divided evenly between
those two things.
That is the wrong balance. Solar panels are nice to have; many
Bangladeshi farmers already possess small ones which they use for charging
mobile phones and powering a couple of light bulbs. But these are no substitute
for reliable electrical power, and there are plenty of more important things.
Diverting money that would otherwise be spent on health and sanitation to
expensive forms of clean energy will make it harder, not easier, for the
world’s poorest people to cope with climate change.
What about carbon tax
A global carbon tax, or even one involving many countries, is likely to
remain an economic theory for a long time. Certainly, nothing of the sort will
be seriously discussed in Paris. Even so, there are three perfectly good things
everybody could be getting on with right away. Two are humdrum, though no less
worthwhile for that. The third requires greater ambition.
First, countries should be nudged to upgrade their promises for cutting
emissions. In advance of the Paris conference, an untidy mess of pledges has
been dumped on the table. Some countries say, fairly straightforwardly, that
they will cut greenhouse-gas emissions by such-and-such a percentage compared
with a particular year. But they pick different base years, invariably ones in
which their emissions were very high, to make their promises look better.
Australia goes for 2005; Russia plumps for 1990, just before its heavy
industries collapsed. Other countries do not even propose to hold emissions to
a specific level. Some countries go in for statistical tricks, arguing, for
example, that their efforts to prevent deforestation should be weighed more
generously. The pledges should be made more comparable.
A good second move would be to ditch the carbon monomania. Tackling
carbon dioxide, the most important greenhouse gas, is essential. Yet aside from
its effect on ocean chemistry and the fact that it is warming the world, though
so gradually that most people cannot detect it, carbon dioxide is innocuous.
And the effects of emissions persist in the atmosphere for so long that even a
drastic cut would have only a slight effect on climate change in the short
term.
Carbon dioxide is not, however, the only greenhouse pollutant. Methane,
black carbon (ie, soot) and hydrofluorocarbons also
warm the world a good deal. It has been estimated that if strong action were
taken to suppress them, the world might be 0.6°C cooler by 2050 than it would
otherwise be, a quick, fairly noticeable change. There is talk of regulating
hydrofluorocarbons under the Montreal Protocol, which cracks down on
ozone-depleting chlorofluorocarbons, an excellent idea.
The best target is black carbon, which comes off open wood fires and out
of the exhaust pipes of unsophisticated diesel vehicles. This is an immediate
killer, and it is easier to tackle than carbon dioxide.
Man-made global cooling?
If spraying seawater into the air would probably cool the Earth,
spraying sulfur into the stratosphere would be almost certain to do so. It has
been done, after all. Volcanoes spew out sulfur that creates particles which
reflect sunlight back into space; those particles also bounce light around the
atmosphere, producing wonderful sunsets. These can cool the Earth
significantly, albeit briefly (see chart): within a year or so the particles
are washed out of the atmosphere.
Sulfur could be sprayed at precisely the right height and in very fine droplets,
which would reflect more light for longer. It might take only a small fleet of
high-altitude aircraft flying in relays to put enough in the stratosphere to
cancel out the entire temperature rise resulting from human greenhouse-gas
emissions. The sulfur would eventually fall as acid rain, but not in alarming
quantities: the amount of sulfur required would be much less than is currently
thrown up into the air by vehicles and factories.
Both marine-cloud brightening and stratospheric aerosols carry risks.
One is that cooling the Earth without removing carbon dioxide does not quite
return the climate to normal. The more carbon dioxide that is present in the
air, the less plants perspire, affecting the water cycle. And the heat-trapping
greenhouse effect would still operate, just with less heat in the system. With
temperatures more evenly distributed in the atmosphere, there would be less
convection and, presumably, less precipitation. So a cooler world with lots of
greenhouse gases would probably be a drier world. Any country that suffered a
drought would surely blame the geoengineers.
But the biggest problem is what would happen if the engineering stopped.
Assuming that greenhouse-gas emissions continued while the ships or aeroplanes were doing their work, abruptly ending the
artificial shielding would lead to a sudden jump in temperatures, which would
be disastrous for people and the natural world alike. Ken Caldeira
of the Carnegie Institution points out that an abrupt “termination shock” could
be avoided if geoengineering were used only to slow global warming and then
gradually wound down. But that assumes the nations of the world can agree on
how to manage the climate. The history of United Nations climate talks suggests
they can’t.
Still, these methods ought to be developed and even, very carefully, tested.
The Earth might need a drastic intervention, particularly if it became clear
that something alarming was about to happen, such as a breakdown of the Indian
monsoon. Marine-cloud brightening could be deployed on a small scale to avert
specific disasters. Mr Latham suggests that cooling
just a few hundred square kilometers of ocean in the right place could make a
hurricane less severe. If the climate-modellers are
right that hurricanes will become more intense as the ocean warms, this will
become increasingly tempting.
The most persuasive reason for investigating geoengineering further is
that somebody is likely to try it. Countries will have different ideas about
when global warming becomes truly dangerous: Britain, for instance, is a lot
more sanguine than the Maldives. Some of the more skittish states might start
injecting aerosols into the lower stratosphere, perhaps in a clumsy way. If no
formal experiments had been carried out and thus scientists in other countries
did not know what to look for, it might not be obvious for some time that this
was going on.
Of course one can doubts that nations would ever formally agree to engineer
the Earth’s climate: their interests are too diverse. What is more likely is
that a country would just go ahead and try it. That would put the others in a
quandary. Should they forcibly stop that country from acting, or should they
step in with superior geoengineering techniques? Before long they could find
themselves acting as zookeepers to the planet.
The most important thing of all however is to innovate.
Hence there is a crying need to develop technologies that are cheaper
and more dependable than today’s wind turbines and solar farms. Bur one can
also hold out hope for artificial photosynthesis, which uses solar energy to
make hydrogen from water.
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