Cities
Across Asia Get Dimmer: Impacts on Glaciers,
Agriculture and the Monsoon Get Clearer
Beijing/Nairobi, 13
November 2008 - Cities from Beijing to New
Delhi are getting darker, glaciers in ranges
like the Himalayas are melting faster and
weather systems becoming more extreme, in
part, due to the combined effects of man-made
Atmospheric Brown Clouds (ABCs) and greenhouse
gases in the atmosphere.
These are among the
conclusions of scientists studying a more
than three km-thick layer of soot and other
manmade particles that stretches from the
Arabian Peninsula to China and the western
Pacific Ocean.
Today the team, drawn
from research centres in Asia including
China and India, Europe and the United States,
announced their latest and most detailed
assessment of the phenomenon.
The brown clouds, the
result of burning of fossil fuels and biomass,
are in some cases and regions aggravating
the impacts of greenhouse gas-induced climate
change, says the report.
This is because ABCs
lead to the formation of particles like
black carbon and soot that absorb sunlight
and heat the air; and gases such as ozone
which enhance the greenhouse effect of CO2.
Globally however brown
clouds may be countering or 'masking' the
warming impacts of climate change by between
20 and up to 80 per cent the researchers
suggest.
This is because of particles
such as sulfates and some organics which
reflect sunlight and cool the surface.
The cloud is also having
impacts on air quality and agriculture in
Asia increasing risks to human health and
food production for three billion people.
Achim Steiner, UN Under-Secretary
General and Executive Director, UN Environment
Programme (UNEP) said: "One of UNEP's
central mandates is science-based early
warning of serious and significant environmental
challenges. I expect the Atmospheric Brown
Cloud to be now firmly on the international
community's radar as a result of today's
report".
The phenomenon has been
most intensively studied over Asia. This
is in part because of the region's already
highly variable climate including the formation
of the annual Monsoon, the fact that the
region is undergoing massive growth and
is home to around half the world's population.
But the scientists today
made clear that there are also brown clouds
elsewhere including over parts of North
America, Europe, southern Africa and the
Amazon Basin which also require urgent and
detailed research.
"Combating rising
CO2 levels and climate change is the challenge
of this generation but it is also the best
bet the world has for Green Growth including
new jobs and new enterprises from a booming
solar and wind industry to more fuel efficient,
vehicles, homes and workplaces. Developed
countries must not only act first but also
assist developing economies with the finance
and clean technology needed to green energy
generation and economic growth," said
Mr Steiner.
"In doing so, they
can not only lift the threat of climate
change but also turn off the soot- stream
that is feeding the formation of atmospheric
brown clouds in many of the world's regions.
This is because the source of greenhouse
gases and soot are often one and the same
- unsustainable burning of fossil fuels,
inefficient combustion of biomass and deforestation,"
he added.
Professor Veerabhadran
Ramanathan, head of the UNEP scientific
panel which is carrying out the research
said: "I would like to pay tribute
to my distinguished colleagues, drawn from
universities and research centres in Asia
including China, India, Japan, Korea, Singapore
and Thailand as well as Europe and the United
States".
"Our preliminary
assessment, published in 2002, triggered
a great deal of awareness but also skepticism.
That has often been the initial reaction
to new, novel and far reaching, counter-intuitive
scientific research," he said.
"We believe today's
report brings ever more clarity to the ABC
phenomena and in doing so must trigger an
international response - one that tackles
the twin threats of greenhouse gases and
brown clouds and the unsustainable development
that underpins both," added professor
Ramanathan who is based at the Scripps Institution
of Oceanography, La Jolla, California.
"One of the most
serious problems highlighted in the report
is the documented retreat of the Hind Kush-Himalayan-Tibetan
glaciers, which provide the head-waters
for most Asian rivers, and thus have serious
implications for the water and food security
of Asia," he said.
"The new research,
by identifying some of the causal factors,
offers hope for taking actions to slow down
this disturbing phenomenon; it should be
cautioned that significant uncertainty remains
in our understanding of the complexity of
the regional effects of ABCs and more surprises
may await us " added Professor Ramanathan.
Highlights from Atmospheric
Brown Clouds: Regional Assessment Report
with Focus on Asia
Five regional hotspots
for ABCs have been indentified. These are:
East Asia, covering eastern China;
The Indo-Gangetic plains
in South Asia from the northwest and northeast
regions of eastern Pakistan across India
to Bangladesh and Myanmar;
Southeast Asia, covering
Cambodia, Indonesia, Thailand, and Vietnam;
Southern Africa extending
southwards from sub-Saharan Africa into
Angola, Zambia and Zimbabwe; and
The Amazon Basin in
South America.
There are hotspots too
in North America over the eastern seaboard
and in Europe - but winter precipitation
tends to remove them and reduce their impact.
Cities and 'Dimming'
Around 13 megacities
have so far been identified as ABC hotpots.
Bangkok, Beijing, Cairo,
Dhaka, Karachi, Kolkata, Lagos, Mumbai,
New Delhi, Seoul, Shanghai, Shenzhen and
Tehran where soot levels are 10 per cent
of the total mass of all human-made particles.
ABCs can reduce sunlight
hitting the Earth's surface in two ways.
Some of the particles
such as sulphates, linked with burning coal
and other fossil fuels, reflect and scatter
rays back into space.
Others, also linked
with fossil fuel and biomass burning, in
particular black carbon in soot, absorb
sunlight before it reaches the ground. The
overall effect is to make 'hot spot' cities
darker or dimmer.
'Dimming' of between 10-25 per cent is occurring
over cities such as Karachi, Beijing, Shanghai
and New Delhi
Guangzhou is among several
cities that have recorded a more than 20
per cent reduction in sunlight since the
1970s
For India as a whole,
the dimming trend has been running at about
two per cent per decade between 1960 and
2000 - more than doubling between 1980 and
2004.
"In China the observed
dimming trend from the 1950s to the 11000s
was about 3-4 per cent per decade, with
the larger trends after the 1970s,"
says the report.
Impact on Cloud Formation
and a Further Dimming Effect
Regions with large concentrations
of ABCs may be getting cloudier which can
also contribute to dimming but data are
not sufficient to quantify this effect.
Particles and aerosols
in the ABCs may act to inhibit the formation
of rain drops and rainfall. "The net
effect is an extension of cloud life-times,"
says the report.
Masking the Impacts
of Climate Change
ABCs shield the surface
from sunlight by reflecting solar radiation
back to space and by absorbing heat in the
atmosphere.
These two dimming phenomena
can act to artificially cool the Earth's
surface especially during dry seasons. The
pollution can also be transported around
the world via winds in the upper troposphere
(above 5 km in altitude).
As a result global temperature
rises - linked with greenhouse gas emissions
- may currently be between 20 per cent and
80 per cent less as a result of brown clouds
around the world says the report.
If brown clouds were
eliminated overnight, this could trigger
a rapid global temperature rise of as much
as to 2 degrees C.
Added to the 0.75 degrees
C rise of the 20th century, this could push
global temperatures well above 2 degrees
C - considered by many scientists to be
a crucial and dangerous threshold.
Thus simply tackling
the pollution linked with brown cloud formation
without simultaneously delivering big cuts
in greenhouse gases could have a potentially
disastrous effect.
Complex Regional Impacts
on Temperature
The science of ABCs,
woven with the science of greenhouse gases,
is not simple and may be behind some highly
complex warming and cooling patterns witnessed
on Continents and in different regions of
specific countries.
The masking of greenhouse
warming by ABCs may in part be the explanation
for the lack of a strong warming trend over
India since the 1950s during the dry season
which runs from January to May.
ABCs may explain in
part why the warming trend in India's night
time temperatures is much larger than the
trend in day time temperatures.
Annual mean temperatures
in mainland China have risen by over one
degree C in the past half century.
However the trends have
not been uniform with the Tibetan Plateau
and the North, Northeast and Northwest of
China experiencing the highest temperature
rises.
Conversely Southwest
and central Eastern China has experienced
a strong cooling trend of between 0.1 to
0.3 degrees C per decade.
"The combined effects
of greenhouse gases, ABCs and rapid urbanization
are required to explain the complex pattern
of warming and cooling trends in China,"
says the report.
Impacts on Weather Patterns
Including the East Asian Monsoon
The large heating and
cooling effects of ABCs respectively in
the atmosphere and at the surface, combined
with the impacts of greenhouse gases, may
be also triggering sharp shifts in weather
patterns.
This is being aggravated
by dimming over the Northern Indian Ocean
versus the relatively clean Southern Indian
Ocean setting up new gradients in surface
sea temperatures and surface sea evaporation
rates.
ABCs, along with the
global warming may thus be acting to trigger
significant drying in northern China and
increased risk of flooding in southern China
while in part also triggering other environmental
and economic effects.
Overall decrease in
monsoon precipitation over India and Southeast
Asia by between five and seven per cent
since the 1950s.
Since the 1950s the
Indian summer monsoon is not only weakening
but shrinking with a decrease in early and
late season rainfall and a decline in the
number of rainy days.
In both China and India
extreme rain events of more than 100 mm
a day have increased.
In both India and China
very heavy rainfall of more than 150 mm
a day have nearly doubled.
Impact on Glaciers
The Hindu Kush-Himalaya-Tibetan glaciers
provide the head-waters for the major river
systems including the Ganges, Brahmaputra,
Mekong and Yangtze rivers.
The Ganges basin is
home to over 400 million people and holds
40 per cent of India's irrigated croplands.
The Chinese Academy
of Sciences estimates that the glaciers
have shrunk five per cent since the 1950s
and the volume of China's nearly 47,000
glaciers has fallen by 3,000 square km over
the past quarter century.
Glaciers in India such
as the Siachen, Gangotri and Chhota Shigiri
glaciers are retreating at rates of between
10 and 25 metres a year. The retreat has
accelerated in the past three and-a-half
decades.
The Gangotri glacier
alone provides up to 70 per cent of the
water in the Ganges.
ABC solar heating of
the atmosphere, due to the absorption of
soot and black carbon pollution "is
suggested to be as important as greenhouse
gas warming in accounting for the anomalously
large warming trend observed in the elevated
regions" such as the Himalayan-Tibetan
region says the report.
Decreased reflection
of solar radiation by snow and ice due to
increasing deposits of black carbon is emerging
as another major contributor to the melting
of ice and snow.
Elevated regions of
the Himalayas within 100 km of Mount Everest
experience large black carbon concentrations
ranging from a few hundred to a few thousand
nano grammes per cubic metre.
Impacts on Agriculture
Impacts of ABCs on food
production and farmers' livelihoods may
be many.
However there remains
a great deal more research to undertake
in terms of crops at risk and the precise
role various ABC-linked effects - separately
or in combination with those of greenhouse
gases - may or may not be having.
Possible effects may
include
Damage to crops as a
result of increased ground level ozone.
In Europe a threshold concentration at which
damage can occur is deemed to be 40 parts
per billion
The report says that
in parts of Asia ground level ozone can
reach 50 parts per billion during February
to June and peaking again between September
and November at 40 parts per billion
The studies suggest
that growing season mean ozone concentrations
in the range 30 - 45 parts per billion could
see crop yield losses in the region of 10
- 40 per cent for sensitive cultivars of
important Asian crops such as wheat rice
and legumes
A recent study translated
such impacts on yield into annual economic
losses estimating that for four key crops
- wheat, rice, corn and soya bean - these
may amount to around $5 billion a year across
China, the Republic of Korea and Japan
Other effects may include
damage linked with the various acidic and
toxic particles from brown clouds depositing
on plants from the atmosphere
Reduced levels of photosynthesis
and thus crop production due to 'dimming'
Health Impacts of ABCs
Brown clouds contain
a variety of toxic aerosols, carcinogens
and particles including particulate matter
(PM) of less than 2.5 microns in width.
These have been linked with a variety of
health effects from respiratory disease
and cardio-vascular problems.
Outdoor exposure - Increases in concentrations
of PM 2.5 of 20 microgrammes per cubic metre
could lead to about 340,000 excess deaths
per year in China and India
Indoor exposure - the
World Health Organization estimates that
over 780,000 deaths in the two countries
can be linked to solid fuel use in the home
Economic losses due
to outdoor exposure to ABC-related PM2.5
has been crudely estimated at 3.6 per cent
of GDP in China and 2.2 per cent of GDP
in India
Notes to Editors
Project Atmospheric
Brown Cloud was established by the United
Nations Environment Programme (UNEP) in
2002 following the documentation of brown
clouds and haze by the Indian Ocean Experiment
(INDOEX).
The science secretariat
of ABC is located at the Center for Clouds,
Chemistry and Climate, Scripps Institution
of Oceanography, UCSD.
The current project
is funded by UNEP with support from the
governments of Italy, Sweden and the United
States.
Atmospheric Brown
Clouds: Regional Assessment Report with
Focus on Asia can be found at www.unep.org
Nick Nuttall, UNEP Spokesperson/Head of
Media
Anne-France White, UNEP Associate Information
Officer