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SPECIAL EDITION
P L A N E TA R Y H E A LT H
From The Economist 2014
In this issue:
Climate change and poverty
The future of the oceans
The melting north
Livestock diseases
China and the environment
Contents
Reprinted from The Economist, 2014
3 Planetary health: Improving well-
being, protecting ecosystems, and
sustaining human civilisations
Breaching planetary boundaries Moving from knowledge to action
4 The global environment 17 Governing the high seas
Boundary conditions In deep water
5 The outlook 19 Governing the oceans
Averting the sixth extinction The tragedy of the high seas
6 Climate science 20 Agricultural biodiversity
A sensitive matter Banking against Doomsday
9 The future of the oceans 21 Brazil’s conversion
Acid test Trees of knowledge
10 The Arctic 23 China and the environment
The melting north The East is grey
Impacts on human well-being 27 Obituary
Elinor Ostrom
13 The rise of Genghis Khan
A horde of data
13 Climate change and civilisation
Time and chance SPECIAL EDITION
P L A N E TA R Y H E A LT H
14 Global health
From The Economist 2014
In this issue:
Lifting the burden
Climate change and poverty
15 Free exchange The future of the oceans
The melting north
The weather report Livestock diseases
China and the environment
16 Livestock diseases
On the zoonose
For more information about
“Planetary health” please go to
www.VisionariesUnbound.com
From the conveners
Reprinted from The Economist, 2014
Planetary Health:
Improving Well-being, Protecting Ecosystems, and Sustaining Human Civilisations
In 2013, Martin Rees, former president of the UK’s diseases, such as smoking and obesity. The complex at Stockholm University, introduced the concept of
Royal Society, a prestigious fellowship of scientists and intertwined nature of global health thus suggests planetary boundaries, or the idea that our species
from every field across science, engineering and an interest in trans-border health issues and solutions, must live within a safe operating space. That space is
medicine, wrote in Science magazine, “The main interdisciplinary study and the integration of public defined by dangers such as ocean acidification, ozone
threats to sustained human existence now come health with the multiple dimensions of health care. depletion, declining freshwater resources, biodiversity
from people, not from nature. We have a limited Global health is an improvement over the concept loss, chemical pollution and climate change. If one or
time base for exposure to [these threats] and can’t that preceded it: international health. The word more of these boundaries is breached, environmental
be so sanguine that we would survive them for long, ‘global’ implies a commitment not only to improving trajectories that veer from their natural path could impact
or that governments could cope if disaster strikes.” health, but also to achieving equity among peoples. planetary systems so severely that the very survival
The first part of Rees’s statement is uncontroversial. Because the concept suggests that individuals and of the human species would be in jeopardy. Already,
It is widely agreed that we live in an anthropocene era, populations are interdependent, global health also Rockström argues, three planetary boundaries have
one in which human activities are perceived to impact demands revisiting the political, economic and social been crossed—those of climate change, biodiversity
our planet’s ecosystems unfavorably. But the second contexts of health and disease. and the global nitrogen cycle.
part is more alarming. Here, he suggests that our Indeed, understanding our current challenges and Since its 2009 introduction, this planetary-
ability to escape these threats may be limited. Dangers finding solutions to them will require far deeper levels boundary approach has captured the imagination
humans face may not be resolved by adapting to or of collaboration between peoples. The values that of many scientists and policymakers. But another
lessening the harm wrought by our activities. Rees is underpin global health have created a new generation dimension should also be considered. Planetary
describing the ultimate threat to human health—our of activism for a healthier and more equitable world. boundaries focus on our planet’s natural systems
species’ extinction by our own hand. But is global health—in both its definition and and how human activity is changing them. But what
Yet there is a paradox in this predicament. In the scope—truly meeting the demands that our societies about human systems—the political, economic, social,
past decade, driven mostly by the United Nations’ currently face? One could argue that global health technical and environmental policies and institutions
Millennium Development Goals (MDGs)—eight goals may still be too narrow to explain and illuminate we create, which together shape the decisions and
for 2015, agreed to by all the world’s countries, some pressing challenges today. Global health does actions that affect our planet’s natural systems? In
including halving poverty and improving maternal not fully take into account the natural foundation other words, what about human civilisations, and how
and child health—a powerful new discipline deeply on which humans live—the planet itself. Nor does it they impact our future? And how will that future, in
concerned with human health and well-being known factor in the force and fragility of human civilisations. turn, affect human civilisations? One could argue that
as ”global health” has emerged. This intense concern Our planet is under increasing pressure, not just the way we organise society’s decisions and actions
with our well-being is reflected in an astonishing from the 2bn more people who will inhabit it between to face planetary threats is more important than the
increase in Development Assistance for Health now and 2050. That is why the post-MDG era is focused threats themselves.
(DAH), or development-focused funds for health on sustainability, or the idea that not only are human Consider these questions: What risks do our
from public and private institutions for low- and and natural systems interdependent, but also that the civilisations face, and how will we identify them?
middle-income countries. deviation of environmental trajectories from their Are we living through a key transition for our species
Before the MDG era (pre-2000), annual growth in natural course could be catastrophic. In this way, and civilisations, and how would we know if we were?
DAH was 5.9%. In 2001, total DAH stood at $10.8bn. But the goals of sustainability differ greatly from those What forces have shaped past civilisations and our
from 2001 onwards, annual DAH growth accelerated as that have dominated the MDG era. Sustainability civilisations today, and what will protect future
high as 11.2% for DAH that totaled US$28.2bn by 2010. means valuing tomorrow as much as today because civilisations? What will determine human sustainability
Shifts in research or policies often reflect the the planet’s potential to sustain the human species is and resilience in the face of these planetary dangers?
concerns of particular times and places. Such is the slowly declining. It means being concerned about all Is human and planetary sustainability compatible
case with global health. Global health has emerged of us, not just some of us. Clearly, the post-2015 era’s with our current expectations for economic growth
at a moment when the risks and drivers shaping most important idea is that global sustainability is and material prosperity?
the health of populations cross national borders in the bedrock of human health, survival and prosperity. To answer these and other questions, The Lancet
entirely new ways, evident in global epidemics and the To more precisely define what it is we must sustain, and The Rockefeller Foundation are launching a
increasingly common causes of non-communicable Johan Rockström, a professor of Environmental Science commission and convening a major global gathering at
the Foundation’s Center in Bellagio, Italy. This special
edition of The Economist magazine will, together with
other inputs, help shape that ongoing conversation.
This commission and the July 2014 Bellagio
Center meeting will investigate the threats to human
civilisations from planetary-system disturbances and
explore a wide range of possible responses to those
threats. It will argue that we need to go beyond even
the broad manifesto of global health, by instead
adopting a whole-planet (planetary) view of human
health and well-being. It will describe the nature of
the systems affecting planetary health, define the
goals of securing planetary health, suggest a roadmap
for achieving these ambitious objectives and propose
concrete actions to do so. Finally, the commission
Richard Horton Robert Garris will seek to identify the concepts, methods and tools
Editor-in-Chief Managing Director necessary to prevent civilisational collapse, and to
The Lancet Bellagio Programs foster the flourishing of human societies. n
The Rockefeller Foundation
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Breaching planetary boundaries
The Economist 2014
Also in this section
5 The outlook
6 Climate science
9 The future of the oceans
10 The Arctic
planetary-boundaries group derives most
of its limits by looking at conditions during
the Holocene—the epoch since the end of
the most recent ice age, in which human
civilisations have grown up. Both of these
criticisms have merit.
For things that clearly do have the springlike
quality of shifting irreversibly if pulled (or
The global environment pushed) too far, like the collapse of ice sheets
Boundary conditions or the melting of permafrost, a boundary
system that seeks to stop you getting too
close to the threshold seems as sensible as
Reprinted from The Economist, Jun 16th 2012 a safety rail is on a parapet. There is good
reason to believe that parts of the climate
The idea of planet-wide environmental reported recently to Ban Ki-moon, the UN’s do behave this way, and thus need railing
boundaries, beyond which humanity would secretary-general, gave the idea pride of place. off. But of the nine boundaries, only three
go at its peril, is gaining ground And Planet Under Pressure, a big scientific apply to systems where the boundary setters
conference held recently in London, made really believe there is a global threshold:
PULL a spring, let it go, and it will snap back boundaries central to the message it sent to the climate; the acidity of the oceans; and
into shape. Pull it further and yet further Rio+20, the UN environmental summit that the ozone layer. Some of the other six may
and it will go on springing back until, quite opens in Brazil on June 20th. have local thresholds, but for the most part
suddenly, it won’t. What was once a spring has their global effects are simply the aggregate
become a useless piece of curly wire. And that, Don’t fence me in of the local ones.
in a nutshell, is what many scientists worry Planetary boundaries provide a useful way Confusing the two might, in the Breakthrough
may happen to the Earth if its systems are of thinking about environmental change, Institute’s view, result in poor policy. Concern
overstretched like those of an abused spring. because in many cases they give scope for over a planet-wide nitrogen limit, for example,
One result of this worry, in the autumn of further change that has not already happened. could lead to people forgoing the benefits
2009, was the idea of planetary boundaries. In That has brought the concept friends who are that fertilisers offer the poor soils of Africa
the run-up to that year’s climate conference in not normally persuaded by environmental on account of harm done by their over-
Copenhagen a group of concerned scientists thinking, as well as green enemies who will application in China.
working under the auspices of the Stockholm brook no compromise. But the concept has The institute’s other criticism is the implicit
Resilience Centre, in Sweden, defined, in a numerous drawbacks. The actual location assumption that because mankind came of age
paper in Nature, what they thought of as a safe of the boundaries is, as their proponents in the Holocene, therefore Holocene conditions
operating space for human development—a acknowledge, somewhat arbitrary. That is are optimal for the species now. There are
set of nine limits beyond which people should partly because of the incomplete state of current indeed reasons to believe some aspects of the
not push their planet. knowledge, but it may remain so however Holocene were optimal. It was a time of climatic
The nine areas of concern were: climate much anyone knows. Some boundaries stability and, in the temperate regions of the
change; ocean acidification; the thinning of might be transgressed without irreversible Earth, clemency. The Breakthrough criticism
the ozone layer; intervention in the nitrogen harm occurring. Some may have been drawn agrees that climate stability is a good thing. It
and phosphate cycles (crucial to plant growth); around the wrong things altogether. And some points out, though, that there is little evidence
the conversion of wilderness to farms and academic opinion holds that spectacular global things like the behaviour of the nitrogen cycle
cities; extinctions; the build up of chemical change could come about without breaking or the phosphate cycle in the Holocene were
pollutants; and the level of particulate pollutants through any of them. particularly well-suited to humans. The fact
in the atmosphere. For seven of these areas The latest criticism comes from the that people have used industrial chemistry
the paper’s authors felt confident enough Breakthrough Institute, a determinedly to short-circuit the nitrogen cycle, by making
to put numbers on where the boundaries heterodox American think-tank that focuses fertilisers out of nitrogen in the air at a rate
actually lay. For chemicals and particulates, on energy and the environment. Among the which greatly exceeds what natural systems
they deferred judgment. points made in a report it published on June can manage, has real environmental effects.
Since then, the idea of planetary boundaries 11th, two stand out. The first is that the idea Nitrate-rich run-off, for example, can wreck the
has taken root. It crops up repeatedly in GEO-5, of boundaries does not focus enough on the ecology of lakes. But if these effects could be
the United Nations Environment Programme’s distinction between things with truly global managed, then it is not clear that the amount
new assessment of the world. The High- effects and those that matter primarily at a of nitrogen being drawn out of the air would,
Level Panel on Global Sustainability, which local or regional level. The second is that the of itself, be a problem.
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Breaching planetary boundaries
The Economist 2014
This is, at bottom, an argument about the rear-view mirror. This reflects the view of tions are improving for other species. That is
nature of the Anthropocene—the age of man. some on the planetary-boundaries team, such thanks to the developments covered in this
Many scientists feel that human interference as James Hansen of the Goddard Institute for special report—shifting public attitudes to other
in the way the Earth works is now so great Space Studies, that today’s climate is already species, increasing appreciation of natural
that the Holocene is history and a truly beyond the point which can guarantee long- environments, legislation to stop the killing of
separate Anthropocene has dawned. The term survival for things like the Greenland endangered species, programmes to eradicate
planetary-boundaries idea seeks to constrain ice sheet, the demise of which would raise invasive species, more and bigger protected
the Anthropocene within the norms of the sea levels by seven metres. areas for wildlife, subsidies to restore degraded
Holocene. The Breakthrough Institute, by If the planetary-boundaries scientists really habitat, better sanitation, better regulation of
contrast, argues for ordering things according have got their sums right, the greenhouse-gas pesticides, decreasing levels of conflict and
to a calculation of the needs of human welfare, situation looks hopeless. From today’s position increasingly effective states implementing
rather than just aping what has happened of carbon-dioxide levels pushing 400ppm and conservationist legislation. All of these become
in the past. There is no doubt as to which going up about 2ppm a year, a carbon-dioxide more prevalent as countries get richer.
of the two approaches is more prudent, and level of 350ppm can be reached only by going Yet the survival of most of the planet’s
prudence always has a constituency. There to zero emissions and then spending a long remaining non-human species is by no means
is plenty of room for debate as to which is time—centuries, in all likelihood—sucking CO2 assured. Leaving aside the huge unknown
more plausible, or practical. out of the atmosphere and putting it back of climate change, whether or not the sixth
underground by various means. great extinction is looming depends largely on
Independence declaration what happens to growth and how humanity
Another problem for the idea of planetary Force majeure manages that growth.
boundaries is the assumption that they Greenhouse gases are, however, only a problem Faster growth will mean higher consumption
are independent of each other. That seems because of their effect on radiative forcing. If of resources and more pressure on habitat,
unlikely, and if they are not then a crisis that could be reined back inside the boundary which is bad for other species. But as North
might arise even if no single boundary were by other means, then the CO2 limit would Korea’s experience shows, the combination
transgressed. On June 7th Nature, which no longer pertain. And that might be possible of economic stagnation and poverty is even
likes to get its oar in before big international by spraying reflective particles into the upper worse. Growth can benefit biodiversity, so
powwows like the ones in Copenhagen and atmosphere, to bounce sunlight back into space. long as it is combined with regulation and
Rio, published a review of evidence that this Such a radical scheme would have all sorts investment to protect other species. That has
may be happening. It suggested that the Earth of disturbing side effects, with political ones happened to some extent; whether it happens
may be approaching a “tipping point” past quite possibly outweighing environmental enough to prevent biodiversity being drastically
which simultaneous changes—to land use, ones. It is by no means clearly the right thing reduced depends largely on governments in
climate and more—driven by an ever larger, to do. But it might be. And it certainly serves emerging markets.
ever richer human population, push the system to show that, although the Earth may have But the biggest question of all for other
into a very different state from its present one, boundaries, thinking about how to help it species is what happens to land use. With
with climate zones changed permanently, should not. n habitat loss the principal threat to biodiversity,
ecosystems functioning differently, and so on. and agriculture taking up two-fifths of land
A sudden shift is plausible. Small ecological compared with 3% for urban areas, the demand
systems, such as lakes, often switch states in for food, and how it is met, will determine
this way and there is no obvious reason why how much land is left for other creatures.
a large system like the Earth should not do The outlook According to research led by David Tilman
likewise. And according to Anthony Barnosky
of the University of California, Berkeley,
Averting the sixth of the University of Minnesota, demand for
food is likely to double by 2050. The UN’s
one of the Nature review’s main authors, a
combination of changes, each itself within
extinction central estimate is for the world’s population
to rise by a third over that period, from 7.2
the planetary boundaries, could still trigger billion to 9.6 billion, but demand for food will
such a change of state. grow faster than that, because as people get
That would be a bad thing. Even if the Reprinted from The Economist, Sep 14th 2013 richer more of them will get enough to eat
ultimate result were an Earth that is still and more will be able to afford more meat.
hospitable to mankind, the transition could Growth is good, but governments need Meat consumption per person in China has
be catastrophic. But the existence of plausible to continue to regulate it and greens to risen from 4kg a year in 1961 to 58kg in 2009.
bad futures within the boundaries raises the learn to love it In Britain it is 84kg.
obverse question: are there good futures outside Assuming that current levels of wastage
them? In particular, might it be possible to OVER THE GRAND sweep of history and persist, if demand for food were to double and
finesse the most famous boundary of all, geography, things have not been going well crop yields remained the same, the amount
the one governing greenhouse warming and for Earth’s non-human species. Extinction of land cultivated would need to double as
climate change? rates over the past few centuries have been well. Since around 40% of the land on the
The planetary-boundaries team, slightly far higher than the background rate, and planet is already cultivated, that would not
confusingly, defines this boundary in two taking the world as a whole the picture over leave much room for other creatures. But if
different ways. One is a limit on carbon the past few decades has been looking pretty farming were to become twice as productive,
dioxide, the main long-lived greenhouse bleak. The Living Planet Index shows a 30% there would be no need to till any more land.
gas, of 350 parts per million (ppm) in the decline in biodiversity since 1970. Over the past 60 years America’s corn farmers
atmosphere. The other is a limit on “radiative Take a closer look, though, and a more have done better than that: production has
forcing”—the increase in energy delivered to optimistic account of the planet’s trajectory quadrupled on an area that has increased by
the surface of the Earth over time, largely as emerges. What limited information on extinc- half (see chart).
a consequence of extra greenhouse gases—of tions is available suggests that trends have
1 watt per square metre above pre-industrial improved recently. Although the LPI shows a Loaves and fishes
levels. Either way, the climate boundary is global fall in biodiversity, and a stark decline For agriculture to pull off the same trick again
one that already lies squarely in humanity’s in poorer countries, in richer countries condi- would mean either boosting yields in high-
5
Breaching planetary boundaries
The Economist 2014
they are its friends. Only through more of
both can man hope to go on enjoying the
company of the 8.7m or so other species with
which he was born to share this planet. n
Climate science
A sensitive matter
Reprinted from The Economist, Mar 30th 2013
The climate may be heating up less in
response to greenhouse-gas emissions than
was once thought. But that does not mean
the problem is going away
Looking for a high-tech solution
yielding countries yet further or intensifying the green movement is understandable.
agriculture in low-yielding countries. The first Environmentalism was partly a response
may be hard to do: agricultural tech companies to “Silent Spring”. Opposition to companies
are struggling to get any more yield out of like Monsanto and Syngenta is bred into the
cereals growing in favourable conditions. green movement. So is hostility to growth:
But there is clearly scope for the second. In environmentalism’s roots lie in the Romantic OVER the past 15 years air temperatures
America, for instance, corn (maize) yields are movement that sprang up in opposition to at the Earth’s surface have been flat while
around 7.7 tonnes per hectare, compared with the industrial revolution. Deep in the green greenhouse-gas emissions have continued
2.5 tonnes in India. movement’s soul lies a belief that the wrongs to soar. The world added roughly 100 billion
Boosting yields means using more fertiliser, done to the planet were caused by technological tonnes of carbon to the atmosphere between
pesticide and GM seeds. Some environmentalists change and economic growth, and that more 2000 and 2010. That is about a quarter of all
understand this, but few publicly support of them can lead only to greater evil. the CO2 put there by humanity since 1750.
the intensification of agriculture. Attitudes It is true that if man had never sharpened And yet, as James Hansen, the head of NASA’s
to GM among the big NGOs range from the his first spear, the mastodons would probably Goddard Institute for Space Studies, observes,
RSPB (“maintains an open mind”) and WWF still be roaming the plains of North America “the five-year mean global temperature has
(“precautionary approach”) to Greenpeace (“a and the aurochs the grasslands of Europe. been flat for a decade.”
serious threat to biodiversity and our own But it is wrong to conclude from this that Temperatures fluctuate over short periods,
health”) and Friends of the Earth (“unnecessary more growth and more technological change but this lack of new warming is a surprise.
risks to both humans and nature”). Among would compound the disaster. For the first Ed Hawkins, of the University of Reading, in
green political activists, hostility to the time since he got the upper hand, it looks Britain, points out that surface temperatures
intensification of agriculture is near-uniform. as though man may succeed in averting since 2005 are already at the low end of
In consequence, GM seeds are, in effect, the sixth great extinction, for a series of the range of projections derived from 20
banned in the European Union (though EU interconnected reasons. climate models (see chart 1). If they remain
citizens feast on GM products freely imported As mankind has got richer, he has set about flat, they will fall outside the models’ range
from other countries) and rich-world activists cleaning up some of the mess that he has
have exported their opposition to GM crops 1
made of his surroundings. Growing prosperity Falling off the scale
to Africa and Asia. has induced him to care about matters Change in global mean temperature, °C
Hostility to intensive agriculture within beyond his own survival and that of his tribe Actual Computer models
and to translate those concerns into laws, 5-95%* 25-75%*
2.0
All ears 7
regulations and programmes, both publicly
US corn
and privately funded, that have changed 1.5
Harvested area, Production,
hectares, m tonnes, m people’s behaviour towards their environment.
50 500 At the same time, the technological progress 1.0
40 400 that has accompanied economic growth has
0.5
30 300
not just made conservation more effective +
but has also enabled man to produce more 0
20 200
of what he wants from less, to the benefit –
10 100 of other species. 0.5
Many in the environmental movement 1950 60 70 80 90 2000 10 20 35
0 0
regard economic growth and technological Source: Ed Hawkins, University *Confidence
1900 10 20 30 40 50 60 70 80 90 2000 13
of Reading; CMIP5 model dataset interval
Source: USDA progress as enemies of biodiversity. Actually,
6
Breaching planetary boundaries
The Economist 2014
more than a 1°C rise in temperature. The correct response would be the one to which
second is that other things, such as adding most of the world pays lip service: rein in the
soot and other aerosols to the atmosphere, warming and the greenhouse gases causing
add to or subtract from the effect of CO2. All it. This is called “mitigation”, in the jargon.
serious climate scientists agree on these two Moreover, if there were an outside possibility
lines of reasoning. But they disagree on the of something catastrophic, such as a 6°C rise,
size of the change that is predicted. that could justify drastic interventions. This
The Intergovernmental Panel on Climate would be similar to taking out disaster insurance.
Change (IPCC), which embodies the mainstream It may seem an unnecessary expense when
of climate science, reckons the answer is about you are forking out for the premiums, but
3°C, plus or minus a degree or so. In its most when you need it, you really need it. Many
recent assessment (in 2007), it wrote that “the economists, including William Nordhaus of
equilibrium climate sensitivity…is likely to be Yale University, have made this case.
in the range 2°C to 4.5°C with a best estimate If, however, temperatures are likely to
of about 3°C and is very unlikely to be less rise by only 2°C in response to a doubling of
than 1.5°C. Values higher than 4.5°C cannot carbon emissions (and if the likelihood of a
be excluded.” The IPCC’s next assessment 6°C increase is trivial), the calculation might
is due in September. A draft version was change. Perhaps the world should seek to
within a few years. recently leaked. It gave the same range of adjust to (rather than stop) the greenhouse-gas
The mismatch between rising greenhouse- likely outcomes and added an upper limit splurge. There is no point buying earthquake
gas emissions and not-rising temperatures is of sensitivity of 6°C to 7°C. insurance if you do not live in an earthquake
among the biggest puzzles in climate science A rise of around 3°C could be extremely zone. In this case more adaptation rather than
just now. It does not mean global warming is damaging. The IPCC’s earlier assessment more mitigation might be the right policy at
a delusion. Flat though they are, temperatures said such a rise could mean that more areas the margin. But that would be good advice
in the first decade of the 21st century remain would be affected by drought; that up to only if these new estimates really were more
almost 1°C above their level in the first decade 30% of species could be at greater risk of reliable than the old ones. And different results
of the 20th. But the puzzle does need explaining. extinction; that most corals would face significant come from different models.
The mismatch might mean that—for some biodiversity losses; and that there would be One type of model—general-circulation
unexplained reason—there has been a temporary likely increases of intense tropical cyclones models, or GCMs—use a bottom-up approach.
lag between more carbon dioxide and higher and much higher sea levels. These divide the Earth and its atmosphere into
temperatures in 2000-10. Or it might be that a grid which generates an enormous number
the 1990s, when temperatures were rising New Model Army of calculations in order to imitate the climate
fast, was the anomalous period. Or, as an Other recent studies, though, paint a different system and the multiple influences upon
increasing body of research is suggesting, it picture. An unpublished report by the Research it. The advantage of such complex models
may be that the climate is responding to higher Council of Norway, a government-funded is that they are extremely detailed. Their
concentrations of carbon dioxide in ways that body, which was compiled by a team led by disadvantage is that they do not respond to
had not been properly understood before. Terje Berntsen of the University of Oslo, uses a new temperature readings. They simulate
This possibility, if true, could have profound different method from the IPCC’s. It concludes the way the climate works over the long
significance both for climate science and for there is a 90% probability that doubling CO2 run, without taking account of what current
environmental and social policy. emissions will increase temperatures by only observations are. Their sensitivity is based upon
1.2-2.9°C, with the most likely figure being 1.9°C. how accurately they describe the processes
The insensitive planet The top of the study’s range is well below the and feedbacks in the climate system.
The term scientists use to describe the way the IPCC’s upper estimates of likely sensitivity. The other type—energy-balance models—are
climate reacts to changes in carbon-dioxide This study has not been peer-reviewed; simpler. They are top-down, treating the Earth
levels is “climate sensitivity”. This is usually it may be unreliable. But its projections are as a single unit or as two hemispheres, and
defined as how much hotter the Earth will get not unique. Work by Julia Hargreaves of representing the whole climate with a few
for each doubling of CO2 concentrations. So- the Research Institute for Global Change in equations reflecting things such as changes
called equilibrium sensitivity, the commonest Yokohama, which was published in 2012, in greenhouse gases, volcanic aerosols and
measure, refers to the temperature rise after suggests a 90% chance of the actual change global temperatures. Such models do not try to
allowing all feedback mechanisms to work (but being in the range of 0.5-4.0°C, with a mean describe the complexities of the climate. That
without accounting for changes in vegetation of 2.3°C. This is based on the way the climate is a drawback. But they have an advantage,
and ice sheets). behaved about 20,000 years ago, at the peak too: unlike the GCMs, they explicitly use
Carbon dioxide itself absorbs infra-red at of the last ice age, a period when carbon- temperature data to estimate the sensitivity
a consistent rate. For each doubling of CO2 dioxide concentrations leapt. Nic Lewis, of the climate system, so they respond to
levels you get roughly 1°C of warming. A rise an independent climate scientist, got an actual climate observations.
in concentrations from preindustrial levels of even lower range in a study accepted for The IPCC’s estimates of climate sensitivity
280 parts per million (ppm) to 560ppm would publication: 1.0-3.0°C, with a mean of 1.6°C. are based partly on GCMs. Because these
thus warm the Earth by 1°C. If that were all His calculations reanalysed work cited by reflect scientists’ understanding of how the
there was to worry about, there would, as it the IPCC and took account of more recent climate works, and that understanding has not
were, be nothing to worry about. A 1°C rise temperature data. In all these calculations, changed much, the models have not changed
could be shrugged off. But things are not that the chances of climate sensitivity above 4.5°C either and do not reflect the recent hiatus in
simple, for two reasons. One is that rising become vanishingly small. rising temperatures. In contrast, the Norwegian
CO2₂ levels directly influence phenomena If such estimates were right, they would study was based on an energy-balance model.
such as the amount of water vapour (also a require revisions to the science of climate So were earlier influential ones by Reto Knutti
greenhouse gas) and clouds that amplify or change and, possibly, to public policies. of the Institute for Atmospheric and Climate
diminish the temperature rise. This affects If, as conventional wisdom has it, global Science in Zurich; by Piers Forster of the
equilibrium sensitivity directly, meaning temperatures could rise by 3°C or more in University of Leeds and Jonathan Gregory
doubling carbon concentrations would produce response to a doubling of emissions, then the of the University of Reading; by Natalia
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Breaching planetary boundaries
The Economist 2014
greenhouse gases. Most climate models reckon climate sensitivity would be lower.
that aerosols cool the atmosphere by about So the explanation may lie in the air—but
0.3-0.5°C. If that underestimated aerosols’ then again it may not. Perhaps it lies in the
effects, perhaps it might explain the lack of oceans. But here, too, facts get in the way.
recent warming. Over the past decade the long-term rise in
Yet it does not. In fact, it may actually be surface seawater temperatures seems to have
an overestimate. Over the past few years, stalled (see chart 2), which suggests that the
measurements of aerosols have improved oceans are not absorbing as much heat from
enormously. Detailed data from satellites the atmosphere.
and balloons suggest their cooling effect is As with aerosols, this conclusion is based on
lower (and their warming greater, where better data from new measuring devices. But
that occurs). The leaked assessment from it applies only to the upper 700 metres of the
the IPCC (which is still subject to review and sea. What is going on below that—particularly
revision) suggested that aerosols’ estimated at depths of 2km or more—is obscure. A study
radiative “forcing”—their warming or cooling in Geophysical Research Letters by Kevin
effect—had changed from minus 1.2 watts Trenberth of America’s National Centre for
per square metre of the Earth’s surface in the Atmospheric Research and others found that
2007 assessment to minus 0.7W/m ² now: ie, 30% of the ocean warming in the past decade
less cooling. has occurred in the deep ocean (below 700
Andronova and Michael Schlesinger, both of One of the commonest and most important metres). The study says a substantial amount
the University of Illinois; and by Magne Aldrin aerosols is soot (also known as black carbon). of global warming is going into the oceans,
of the Norwegian Computing Centre (who is This warms the atmosphere because it absorbs and the deep oceans are heating up in an
also a co-author of the new Norwegian study). sunlight, as black things do. The most detailed unprecedented way. If so, that would also
All these found lower climate sensitivities. study of soot was published in January and help explain the temperature hiatus.
The paper by Drs Forster and Gregory found also found more net warming than had
a central estimate of 1.6°C for equilibrium previously been thought. It reckoned black Double-A minus
sensitivity, with a 95% likelihood of a 1.0-4.1°C carbon had a direct warming effect of around Lastly, there is some evidence that the natural
range. That by Dr Aldrin and others found a 1.1W/m ². Though indirect effects offset some (ie, non-man-made) variability of temperatures
90% likelihood of a 1.2-3.5°C range. of this, the effect is still greater than an earlier may be somewhat greater than the IPCC
It might seem obvious that energy-balance estimate by the United Nations Environment has thought. A recent paper by Ka-Kit Tung
models are better: do they not fit what is actually Programme of 0.3-0.6W/m ². and Jiansong Zhou in the Proceedings of the
happening? Yes, but that is not the whole All this makes the recent period of flat National Academy of Sciences links temperature
story. Myles Allen of Oxford University points temperatures even more puzzling. If aerosols changes from 1750 to natural changes (such as
out that energy-balance models are better at are not cooling the Earth as much as was sea temperatures in the Atlantic Ocean) and
representing simple and direct climate feedback thought, then global warming ought to be suggests that “the anthropogenic global-warming
mechanisms than indirect and dynamic ones. gathering pace. But it is not. Something must trends might have been overestimated by a
Most greenhouse gases are straightforward: be reining it back. One candidate is lower factor of two in the second half of the 20th
they warm the climate. The direct impact of climate sensitivity. century.” It is possible, therefore, that both
volcanoes is also straightforward: they cool it A related possibility is that general-circulation the rise in temperatures in the 1990s and the
by reflecting sunlight back. But volcanoes also climate models may be overestimating the flattening in the 2000s have been caused in
change circulation patterns in the atmosphere, impact of clouds (which are themselves part by natural variability.
which can then warm the climate indirectly, influenced by aerosols). In all such models, So what does all this amount to? The scientists
partially offsetting the direct cooling. Simple clouds amplify global warming, sometimes are cautious about interpreting their findings.
energy-balance models cannot capture this by a lot. But as the leaked IPCC assessment As Dr Knutti puts it, “the bottom line is that
indirect feedback. So they may exaggerate says, “the cloud feedback remains the most there are several lines of evidence, where the
volcanic cooling. uncertain radiative feedback in climate models.” observed trends are pushing down, whereas
This means that if, for some reason, there It is even possible that some clouds may the models are pushing up, so my personal
were factors that temporarily muffled the dampen, not amplify global warming—which view is that the overall assessment hasn’t
impact of greenhouse-gas emissions on global may also help explain the hiatus in rising changed much.”
temperatures, the simple energy-balance temperatures. If clouds have less of an effect, But given the hiatus in warming and all the
models might not pick them up. They will new evidence, a small reduction in estimates
be too responsive to passing slowdowns. In of climate sensitivity would seem to be
2
short, the different sorts of climate model The cool sea justified: a downwards nudge on various best
measure somewhat different things. Upper-ocean heat-content anomaly, zettajoules* estimates from 3°C to 2.5°C, perhaps; a lower
ceiling (around 4.5°C), certainly. If climate
50
Clouds of uncertainty scientists were credit-rating agencies, climate
This also means the case for saying the climate is 25 sensitivity would be on negative watch. But
less sensitive to CO2 emissions than previously + it would not yet be downgraded.
0
believed cannot rest on models alone. There – Equilibrium climate sensitivity is a benchmark
must be other explanations—and, as it happens, 25 in climate science. But it is a very specific
there are: individual climatic influences and measure. It attempts to describe what would
50
feedback loops that amplify (and sometimes happen to the climate once all the feedback
moderate) climate change. 75 mechanisms have worked through; equilibrium
Begin with aerosols, such as those from in this sense takes centuries—too long for
100 most policymakers. As Gerard Roe of the
sulphates. These stop the atmosphere from 1993 95 2000 05 10 12
warming by reflecting sunlight. Some heat University of Washington argues, even if
Source: Pacific Marine
it, too. But on balance aerosols offset the Environmental Laboratory *1021 joules climate sensitivity were as high as the IPCC
warming impact of carbon dioxide and other suggests, its effects would be minuscule
8
Breaching planetary boundaries
The Economist 2014
under any plausible discount rate because it Patchier data that go back further suggest
operates over such long periods. So it is one there has been a 26% rise in oceanic acidity
thing to ask how climate sensitivity might be since the beginning of the industrial revolution,
changing; a different question is to ask what 250 years ago. Projections made by assuming
the policy consequences might be. that carbon-dioxide emissions will continue
For that, a more useful measure is the transient to increase in line with expected economic
climate response (TCR), the temperature you growth indicate this figure will be 170% by 2100.
reach after doubling CO2 gradually over 70 Worrying about what the world may be
years. Unlike the equilibrium response, the like in nine decades might sound unnecessary,
transient one can be observed directly; there is given more immediate problems, but another
much less controversy about it. Most estimates prediction is that once the seas have become
put the TCR at about 1.5°C, with a range of more acidic, they will not quickly recover their
1-2°C. Isaac Held of America’s National Oceanic alkalinity. Ocean life, in other words, will have
and Atmospheric Administration recently to get used to it. So does this actually matter?
calculated his “personal best estimate” for The variable people most worry about is
the TCR: 1.4°C, reflecting the new estimates called omega. This is a number that describes
for aerosols and natural variability. how threatening acidification is to seashells
That sounds reassuring: the TCR is below and skeletons. Lots of these are made of
estimates for equilibrium climate sensitivity. But calcium carbonate, which comes in two
the TCR captures only some of the warming that crystalline forms: calcite and aragonite. Many
those 70 years of emissions would eventually critters, especially reef-forming corals and
generate because carbon dioxide stays in the free-swimming molluscs (and most molluscs
atmosphere for much longer. are free-swimming as larvae), prefer aragonite
As a rule of thumb, global temperatures for their shells and skeletons. Unfortunately,
rise by about 1.5°C for each trillion tonnes of this is more sensitive to acidity than calcite is.
carbon put into the atmosphere. The world has An omega value for aragonite of one is
pumped out half a trillion tonnes of carbon the level of acidity where calcium carbonate
since 1750, and temperatures have risen by That well-being, some fear, is under threat from dissolves out of the mineral as easily as it
0.8°C. At current rates, the next half-trillion the increasing amount of carbon dioxide in the precipitates into it. In other words, the system
tonnes will be emitted by 2045; the one after atmosphere, a consequence of industrialisation. is in equilibrium and shells made of aragonite
that before 2080. This concern is separate from anything caused will not tend to dissolve. Merely creeping
Since CO2 accumulates in the atmosphere, by the role of CO2 as a climate-changing above that value does not, however, get you
this could increase temperatures compared greenhouse gas. It is a result of the fact that out of the woods. Shell formation is an active
with pre-industrial levels by around 2°C even CO2, when dissolved in water, creates an acid. process, and low omega values even above
with a lower sensitivity and perhaps nearer to That matters, because many creatures which one make it hard. Corals, for example, require
4°C at the top end of the estimates. Despite alllive in the ocean have shells or skeletons an omega value as high as three to grow their
the work on sensitivity, no one really knows made of stuff that dissolves in acid. The stony skeletons prolifically.
how the climate would react if temperatures more acidic the sea, the harder they have As the map above shows, that could be
rose by as much as 4°C. Hardly reassuring. n to work to keep their shells and skeletons a problem by 2100. Low omega values are
intact. On the other hand, oceanic plants, spreading from the poles (whose colder waters
cyanobacteria and algae, which use CO2 for dissolve carbon dioxide more easily) towards
photosynthesis, might rather like a world the tropics. The Monterey report suggests that
where more of that gas is dissolved in the the rate of erosion of reefs could outpace reef
water they live in—a gain, rather than a loss, building by the middle of the century, and that
The future of the oceans to ocean productivity. all reef formation will cease by the end of it.
Acid test Two reports attempting to summarise the
world’s rather patchy knowledge about what
Other species will suffer, too. A study
published in Nature last year, for example,
is going on have recently been published. Both looked at the shells of planktonic snails
are the products of meetings held last year called pteropods. In Antarctic waters, which
Reprinted from The Economist, Nov 23rd 2013 (the wheels grind slowly in environmental already have an omega value of one, their
bureaucracy). One, in Monterey, California,
The world’s seas are becoming more acidic. looked at the science. The other, in Monaco,
How much that matters is not yet clear. looked at possible economic consequences. More vinegar with the fish
But it might matter a lot Together, the documents suggest this is an to come
Atmospheric concentration of CO2 Ocean pH level
issue that needs to be taken seriously, though Annual average, parts per million Trend line
HUMANS, being a terrestrial species, are worryingly little is known about it.
400 8.25
pleased to call their home “Earth”. A more
honest name might be “Sea”, as more than Omega point 375 8.20
seven-tenths of the planet’s surface is covered Regular, direct measures of the amount of
with salt water. Moreover, this water houses CO2 in the air date to the 1950s. Those of the 350 8.15
algae, bacteria (known as cyanobacteria) and oceans’ acidity began only in the late 1980s 325 8.10
plants that generate about half the oxygen (see chart). Since it started, that acidity has
in the atmosphere. And it also provides risen from pH 8.11 to pH 8.06 (on the pH scale, 300 8.05
seafood—at least 15% of the protein eaten lower numbers mean more acid). This may
by 60% of the planet’s human population, not sound much, but pH is a logarithmic scale. 275 8.00
an industry worth $218 billion a year. Its A fall of one pH point is thus a tenfold rise
1959 70 80 90 2000 12
well-being is therefore of direct concern in acidity, and this fall of 0.05 points in just
Sources: NOAA; Scripps Institution of Oceanography
even to landlubbers. over three decades is a rise in acidity of 12%.
9
Breaching planetary boundaries
The Economist 2014
shells were weak and badly formed when
compared with those of similar species
found in warmer, more northerly waters.
Earlier work on other molluscs has come
to similar conclusions.
Not everything suffers from more dissolved
CO2, though. The Monterey report cites studies
which support the idea that algae, cyanobacteria
and sea grasses will indeed benefit. One
investigation also suggests acidification may
help cyanobacteria fix nitrogen and turn it
into protein. Since a lack of accessible nitrogen
keeps large areas of the ocean relatively sterile,
this, too could be good for productivity.
The Monaco report attempts to identify
fisheries that will be particularly affected by
these changes. These include the Southern
Ocean (one of the few areas not already
heavily fished) and the productive fishery off
the coast of Peru and northern Chile, where
upwelling from the deep brings nutrients to
the surface, but which is already quite acidic.
The principal threat here, and to similar
fisheries, such as that off the west coast of
North America, is to planktonic larvae that
fish eat. Oyster and clam beds around the
world are also likely to be affected—again, the
larvae of these animals are at risk. The report
does not, though, investigate the possibility of
increases in algal plankton raising the oceans’ the Nile. Greenland, the world’s biggest island,
overall productivity. is six times the size of Germany. Yet it has a
At the back of everyone’s mind (as in The Arctic population of just 57,000, mostly Inuit scattered
wider discussions of climate change) are
events 56m years ago. At that time, the The melting north in tiny coastal settlements. In the whole of the
Arctic—roughly defined as the Arctic Circle and
boundary between the Palaeocene and Eocene a narrow margin to the south (see map)—there
geological epochs, carbon-dioxide levels are barely 4m people, around half of whom
rose sharply, the climate suddenly warmed Reprinted from The Economist, Jun 16th 2012 live in a few cheerless post-Soviet cities such as
(by about 6°C) and the seas became a lot Murmansk and Magadan. In most of the rest,
more acidic. Many marine species, notably The Arctic is warming twice as fast as the including much of Siberia, northern Alaska,
coccolithophores (a group of shelled single- rest of the planet, says James Astill. The northern Canada, Greenland and northern
celled algae) and deep-dwelling foraminifera retreating ice offers access to precious Scandinavia, there is hardly anyone. Yet the
(a group of shelled protozoa), became extinct minerals and new sea lanes—but also region is anything but inviolate.
in mere centuries, and some students of carries grave dangers
the transition think the increased acidity Fast forward
was more to blame for this than the rise in STANDING ON THE Greenland ice cap, it is A heat map of the world, colour-coded for
temperature. Surface-dwelling foraminifera, obvious why restless modern man so reveres temperature change, shows the Arctic in sizzling
however, thrived, and new coccolithophore wild places. Everywhere you look, ice draws maroon. Since 1951 it has warmed roughly
species rapidly evolved to replace those the eye, squeezed and chiselled by a unique twice as much as the global average. In that
that had died out. coincidence of forces. Gormenghastian ice period the temperature in Greenland has gone
On land, too, some groups of animals did ridges, silver and lapis blue, ice mounds up by 1.5°C, compared with around 0.7°C
well. Though the rise of the mammals is often and other frozen contortions are minutely globally. This disparity is expected to continue.
dated from 66m years ago, when a mass observable in the clear Arctic air. The great A 2°C increase in global temperatures—which
extinction of the dinosaurs left the planet glaciers impose order on the icy sprawl, appears inevitable as greenhouse-gas emissions
open for colonisation by other groups, it is flowing down to a semi-frozen sea. soar—would mean Arctic warming of 3-6°C.
actually the beginning of the Eocene, 10m The ice cap is still, frozen in perturbation. Almost all Arctic glaciers have receded.
years later, which marks the ascendancy of There is not a breath of wind, no engine’s The area of Arctic land covered by snow in
modern mammal groups. sound, no bird’s cry, no hubbub at all. Instead early summer has shrunk by almost a fifth
Oceanic acidity levels appear now to be of noise, there is its absence. You feel it as a since 1966. But it is the Arctic Ocean that is
rising ten times as fast as they did at the pressure behind the temples and, if you listen most changed. In the 1970s, 80s and 90s the
end of the Palaeocene. Some Earth scientists hard, as a phantom roar. For generations of minimum extent of polar pack ice fell by
think the planet is entering, as it did 56m frosty-whiskered European explorers, and around 8% per decade. Then, in 2007, the sea
years ago, a new epoch—the Anthropocene. still today, the ice sheet is synonymous with ice crashed, melting to a summer minimum
Though the end of the Palaeocene was an the power of nature. of 4.3m sq km (1.7m square miles), close to
extreme example, it is characteristic of The Arctic is one of the world’s least explored half the average for the 1960s and 24% below
such transitions for the pattern of life to and last wild places. Even the names of its seas the previous minimum, set in 2005. This left
change quickly. Which species will suffer and rivers are unfamiliar, though many are the north-west passage, a sea lane through
and which will benefit in this particular vast. Siberia’s Yenisey and Lena each carries Canada’s 36,000-island Arctic Archipelago,
transition remains to be seen. n more water to the sea than the Mississippi or ice-free for the first time in memory.
10Breaching planetary boundaries
The Economist 2014
Scientists, scrambling to explain this, found
that in 2007 every natural variation, including
warm weather, clear skies and warm currents,
Summer sea-ice extent:
had lined up to reinforce the seasonal melt.
September 2011
But last year there was no such remarkable
Average 1979-2000
coincidence: it was as normal as the Arctic
gets these days. And the sea ice still shrank Yenisey
to almost the same extent. 90° E
There is no serious doubt about the basic Sea of R L
U S S I A
I A
cause of the warming. It is, in the Arctic as
en
Okhotsk ° R
a
everywhere, the result of an increase in heat- E
.6
Kara Sea
66
Magadan B
trapping atmospheric gases, mainly carbon
E-
I Murmansk D Helsinki
dioxide released when fossil fuels are burned. LAN
RCL
FIN
Barents Stockholm
Because the atmosphere is shedding less solar
C CI
S W E D E N Copenhagen
S
Sea Tromso
heat, it is warming—a physical effect predicted
ARCTI
East N OReitan
back in 1896 by Svante Arrhenius, a Swedish Siberian SVALBARD R W A Y Oslo
North DENMARK
scientist. But why is the Arctic warming faster Sea Pole
(to NORWAY)
Ny-Alesund
than other places? 180° Fram 0° North Sea
B e ri n g Strait Greenland Norwegian
Consider, first, how very sensitive to Se a Bering A R C T I C Sea
Strait Sea
temperature change the Arctic is because of O C E A N
where it is. In both hemispheres the climate Nome
ICELAND
system shifts heat from the steamy equator to GREENLAND
the frozen pole. But in the north the exchange ALASKA Beaufort (to DENMARK)
(to UNITED Sea
is much more efficient. This is partly because STATES) Baffin Jakobshavn
Isbrae ATLANTIC
of the lofty mountain ranges of Europe, Bay
Asia and America that help mix warm and OCEAN
PACIFIC C A N A D A Nuuk
cold fronts, much as boulders churn water OCEAN
in a stream. Antarctica, surrounded by the 90° W
vast southern seas, is subject to much less
atmospheric mixing.
ce
Vi
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Possible shipping routes: e
ai
d
gr cs
The land masses that encircle the Arctic ap
hi cti
c: Northern Sea Route ar
Wa (North-east passage) om/
also prevent the polar oceans revolving tch
our ist
.c
North-west passage om
around it as they do around Antarctica. ani
ma
tion at: Ec
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of ck
Instead they surge, north-south, between the the r
ecedi ld unlo
ng Arc it cou
Arctic land masses in a gigantic exchange tic ice-shelf and the shipping routes
of cold and warm water: the Pacific pours
through the Bering Strait, between Siberia
and Alaska, and the Atlantic through the which melts more snow and ice, revealing Arctic change will be felt much more widely.
Fram Strait, between Greenland and Norway’s more dark land or water, and so on. Known Melting sea ice will not affect global sea
Svalbard archipelago. as the albedo effect, this turns out to be a levels, because floating ice displaces its own
That keeps the average annual temperature more powerful positive feedback than most mass in seawater. But melting glaciers will,
for the high Arctic (the northernmost fringes researchers had expected. Most climate models and the Arctic’s are shedding ice at a great rate.
of land and the sea beyond) at a relatively predicted that the Arctic Ocean could be ice- Greenland’s ice cap is losing an estimated 200
sultry -15°C; much of the rest is close to melting- free in summer by the end of this century; an gigatonnes of ice a year, enough to supply a
point for much of the year. Even modest analysis published in 2009 in Geophysical billion people with water. The Arctic’s smaller
warming can therefore have a dramatic effect Research Letters suggested it might happen as ice caps and glaciers together are losing a
on the region’s ecosystems. The Antarctic is early as 2037. Some now think it will be sooner. similar amount. Before this became clear, the
also warming, but with an average annual It is hard to exaggerate how dramatic this Intergovernmental Panel on Climate Change
temperature of -57°C it will take more than a is. Perhaps not since the felling of America’s (IPCC) had predicted a sea-level rise of up
few hot summers for this to become obvious. vast forests in the 19th century, or possibly to 59cm during this century. Given what is
since the razing of China’s and western happening up north, many now think this
The albedo effect Europe’s great forests a thousand years before too modest.
The efficient north-south mixing of air may that, has the world seen such a spectacular A wilder fear is that a deluge of Arctic
also play a part in the Arctic’s amplified environmental change. The consequences for meltwater could disrupt the mighty “overturning
warming. The winds that rush northwards Arctic ecosystems will be swingeing. circulation” of the global oceans, the exchange
carry pollutants, including soot from European As their ancient ice buffers vanish, Arctic of warm tropical and cold polar water. It has
and Asian smokestacks, which has a powerful coastlines are eroding; parts of Alaska are happened before, at least seven times in the
warming effect over snow. In recent decades receding at 14 metres (45 feet) a year. Niche past 60,000 years, and needs watching. But
there has also been a rise in levels of mercury, habitats, such as meltwater pools on multi-year recent evidence suggests that such a calamity is
a by-product of burning coal, in the tissues of ice, are dwindling. Some highly specialised not imminent. Another concern, that thawing
beluga whales, walruses and polar bears, all Arctic species will probably become extinct as Arctic permafrost could release vast quantities
of which the Inuit eat. This is another reason their habitats shrink and southern interlopers of carbon dioxide and methane, looms larger.
why the Arctic is not virgin. rush in. Others will thrive. The early signs of That, too, has happened before, around 55m
But the main reason for Arctic amplification this biological reshuffle are already evident. years ago, leading to a global temperature
is the warming effect of replacing light-coloured High-Arctic species, including the polar bear, increase of 5°C in a few thousand years.
snow and ice with darker-coloured land or are struggling. Species new to the region, such Such risks are hard to pin down, and possibly
water. Because dark surfaces absorb more heat as mackerel and Atlantic cod, are coming up small. Many elements of the change in the
than light ones, this causes local warming, in Arctic trawler nets. Yet the shock waves of Arctic, including the rates of snow melt and
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