Europe’s showpiece in climate monitoring is called Envisat. Fully
equipped, the largest, most complex, and most powerful Earth observation
satellite of the European Space Agency (ESA) is 25 meters high, ten meters
wide and weighs over eight tons, scheduled for launch in the night of 28
February /1st March on an Ariane 5 launcher. Europe’s flying behemoth is
on the trail of climate change. It will deliver data about global warming,
ozone depletion and climate change for at least five years. The
information is absolutely necessary and long overdue as the basis for
political decisions about climate change.
Until now only a privileged few men and women have been able to see the
Earth from outer space and to recognize how tiny and fragile it is. “I
hope,” said Alexei Leonow, the first cosmonaut to step out of his space
vehicle, “that people understand that and protect our blue planet as their
place of birth, as their common homeland, and as the ancestral home where
their children and grandchildren will live after them.”
Envisat will fulfill this desire. With its ten instrument systems it is
equipped with the best eyes possible and offers everything that scientists
could wish for in the service of the environmentally endangered planet.
The unique flying environment station follows in the footsteps of the
successful European Earth remote sensing satellites ERS 1 (1991) and ERS 2
(1995). Climate protection is a challenge for the entire society. This is
why ESA did not hold back with the budget. The total costs
for the Envisat-Program were 2.3 billion euros, distributed over 15 years.
Included in this sum is development and construction of the instruments as
well as the satellites, the launch on board Ariane 5 and the operational
costs of the satellite for five years. Each citizen of the 15 ESA Member
States thereby invested 7 Euros in the environment. Put another way,
Envisat will cost each European citizen about one cup of coffee per year.
For his money, for at least five years, the citizen receives precise
information about changes in the environment including global warming,
ozone depletion and climate change. This information is absolutely
necessary and long overdue as the basis for political decisions. The gas
envelope of the Earth is not determined by political boundaries. The
atmosphere is global and the circulation is planetary. Letting down the
environmental guard is not possible in Europe or anywhere else.
The Sick Earth Atmosphere
The symptoms are unambiguous: The Earth atmosphere is sick. How sick is
being debated by the scientists. The threat to the environment appears in
a fleeting disguise. It is made of gases which are streaming from the
chimneys and smokestacks of our homes and factories, which are created by
the combustion of wood, coal, oil and gas as well as slash and burn
agriculture, the emissions from automobiles or airplanes, the flatulence
of cows, and what spray cans, foaming agents, solvents, coolants and
cleaning fluids release in the air. Among other such gases, are carbon
monoxide, carbon dioxide, methane, ozone, nitrogen and CFC’s but also
water vapor. Although they make up on a small percentage of the total
amount of trace gases, they could none the less become the instigators of
global climate change. As is so often the case, it depends on the dose.
For several decades a steady increase in the atmosphere of climate-active
gases has been registered. What is disturbing is that the processes are
occurring by degrees. All substances released into the atmosphere have an
effect, somewhere, somehow. The when, where and with which intensity and
consequences is very difficult to understand because of the complexity of
the climate processes and because the feed-back mechanisms are very
difficult to predict. Everything is connected with everything else. “When
I began to investigate the atmosphere, I concentrated exclusively on four
chemical reactions which at the time were considered to be decisive”,
reports Paul Crutzen, who received the Nobel Prize for chemistry in 1995
for his investigation of the cause of the ozone hole. “Today we have to
work with hundreds of reactions in our chemical models if we wish to
understand something.”
One cannot say with certainty in all cases whether certain substances are
neutral or harmful. The best example is CFC’s. The have enjoyed a
remarkable career and metamorphosis. Discovered 70 years ago, they were
long considered to be absolutely harmless, neutral and to a great extent
environmentally benign because they are colorless and odorless and neither
poisonous, corrosive, nor combustible. They were correspondingly in wide
use – as a propellant in spray cans, coolant in refrigerators and air
conditioners, as foaming agent for plastic manufacture, as sterilizing
agent for medical implements, as solvent and cleaning fluid for cloth and
leather and as a cleaning agent for integrated circuits for the
micro-electronics industry.
Environmentally benign CFC’s were then declared ozone killers. In the
meantime, that they destroy the ozone layer and cause the infamous ozone
hole over the Antarctic has become common knowledge. The perpetrator and
the victim can be widely separated from each other in time and place.
Therefore the example makes clear how very important it is to have an
overview of the Earth atmosphere system in order to understand climate
processes.
Science has its own way of acting. The mutual interests of theoreticians
who develop the models of the atmosphere and the technicians who carry out
measurements and build instruments proved to be extremely useful. The two
climate celebrities, the long-time director of the Max-Planck-Institute
for Chemistry at the University of Mainz, the Dutchman Paul Crutzen, and
the Briton John Burrows, specialist in chemistry of the atmosphere at the
Institute for Environmental Physics and Remote Sensing at the University
of Bremen, personify a knowledge enriching symbiosis of this kind. They
enjoy a long friendship with each other. In the mid 80’s, as director of
an international group of scientists, John Burrows suggested the ozone
instruments GOME and SCIAMACHY for the ERS satellite as well as Envissat
and looked after these projects. Burrows has this to say about Crutzen:
“He was an important supporter of the ESA-environmental satellite project
Envisat. He is however primarily a modeler while I am an experimenter.
That is how we continually supplement each other so well.”
Ozone – the Life-Giving Poison
One of the most important greenhouse gases is ozone, a gas with a Janus
face. We encounter it on the surface of the Earth and up to an altitude of
110 kilometers. Approximately 10 % is found in the troposphere, 90 % in
the stratosphere, and the percentage in the mesosphere is insignificant.
The greatest concentration of ozone is in the stratosphere from 18 to 30
kilometers over the equator and 12 to 25 km over the upper latitudes.
Billions of years ago stratospheric ozone made possible life on this
planet. It protects us today from the harmful effects of the ultraviolet
radiation of the sun. We could not survive without the ozone in the
atmosphere. Ozone in the upper troposphere also contributes somewhat as a
filter against UV-radiation. But ozone at ground level is a health
problem. It is a main ingredient of smog. High ozone concentrations in the
lower troposphere are poison for human, animal and plant life. “On the
other hand we need ozone in the troposphere”, explains Paul Crutzen, his
voice rising, “because it is responsible for the formation of hydroxide
radicals (OH). They ensure that almost all substances which make their
ways into the atmosphere become oxidized and removed from the atmosphere.
Hydroxide radicals in combination with the UV-radiation constitute the
“universal cleansing agent” of the atmosphere.”
Holes in the Protective Shield
The problem of global warming is frequently confused with the ozone hole.
There is a connection because ozone contributes to global warming and
there are also mutual correlations. However they are two completely
separate issues. In 1985 British researchers discovered the notorious
ozone hole over Antarctica. It begins every year in spring in the southern
hemisphere, which corresponds to our autumn. It only became clear years
later that the dramatic ozone depletion was mainly due to chlorine
radicals in the atmosphere and that the entire process depends on ice
particles. A decisive part of the explanation of this riddle was provided
by the Max-Planck-Institute for Chemistry in Mainz.
It had been going on already in the 70’s but was first identified in 1985.
Every year the same process began over the South Pole: In the Antarctic
spring, i.e. our autumn, the ozone layer in the stratosphere collapsed.
The development was dramatic. From year to year the surface of the ozone
hole grew larger. It is presently about 25 million square kilometers. At
the same time the duration increased. The rapid thinning of the ozone
starts at the end of September and lasts until December.
Similar phenomena are increasing in the northern Hemisphere. Of course,
according to Crutzen, “that is connected with certain meteorological
phenomena and the intensities are highly variable.” The ozone hole over
the northern polar region in spring also occurs in the stratosphere at
about 12 to 22 kilometers altitude. This is also clearly caused by CFC’s,
that is, it has a man-made origin. Also in mid-latitudes, for instance
over Berlin, already in March, at an altitude of 20 kilometers, so-called
polar stratospheric clouds have been detected. These are an aggressive
mixture of ice and water particles, sulfur and potassium nitrate acid in
which chlorine compounds are converted into ozone killing chlorine
radicals. The result is a region of reduced ozone which is often described
as an ozone “hole”.
The actual threat from increasing ozone depletion and holes in the
atmosphere is the damage done to the UV-screen. The ozone layer works like
a pair of oversized sun glasses. Behind them, living creatures are spared
the greater part of harmful UV-radiation. The reduction of the ozone
concentration in the stratosphere thereby leads to a weakening of this
screen effect. The consequences are damage to the eyes, skin cancer and a
weakening of the immune system. However UV-radiation is also governed by
strong natural variations. How much of the UV-radiation is due to
“natural” causes and how much is due to the ozone depletion is still
unclear. Empirical investigations in northern and middle Europe show a UV
rise per year of .5% in the last ten years. During the time of the
northern ozone maximum, i.e. from January until March, the UV radiation
can even rise 30% in a short period of time. This is of particular concern
for ski vacationers. Apropos vacations: In the future at beaches and
mountain regions there will be a special UV radiation weather report, a
kind of “by-product” of Envisat’s global, precise ozone measurement.
A new cycle of destruction discovered
A new ozone phenomenon at the North Pole in the lowest layer of the
atmosphere, the troposphere, has been found. Several times during the
arctic spring ozone disappears completely over an area of several thousand
square kilometers. Paul Crutzen explains the situation: “The process
happens very quickly. In just a few hours all the ozone can be destroyed.
However in contrast to ozone depletion in the stratosphere this ozone hole
has no negative effects. To the contrary: Ground level ozone is unhealthy
in higher concentrations; we notice this especially with smog at the
height of summer. The bewildering observation was fascinating and at the
same time unsettling. It shows that the chemistry of the atmosphere still
has surprises in store and that science by no means understands all of the
processes which occur in the atmosphere.”
Measurements on Spit Bergen as well as in Canada showed that the ozone
hole in the troposphere as well as its counterpart in the stratosphere
have something in common: In each case some substance acts as a catalytic
which reduces ozone to a normal diatomic oxygen molecule, but which is
itself not used up. Therefore the smallest amounts of such a substance can
have an enormously destructive effect. The catalytic in the stratosphere
is chlorine and in the troposphere it is bromine. The GOME-detector of the
European Earth reconnaissance satellite ERS 2 has provided the proof for
this. One particle of bromine, bromine oxide (BrO) in 100 billion
molecules of air, is enough to start the aggressive destruction of ozone.
If bromine is so aggressive, the question arises, why can it remain in the
troposphere so long? After all, there are countless floating particles in
this region, so-called aerosol particles, which capture this kind of
substance and in this way, take it out of circulation. “More precise
investigations show “, as Crutzen explains the next bewildering
realization, “that the aerosol particles in fact do exactly the opposite.
In their interior chemical reactions take place which recycle inactive
forms of bromine into reactive forms. One part of the aerosol consists of
salt water droplets which contain bromine and which support the catalytic
process even more.”
Where does the bromine come from, though? And why does the ozone depletion
only take place in spring? Seawater is seen to be the main source of
destructive bromine. One assumes that salt aerosols “form deposits during
the arctic night at the borders of the pack ice and gradually accumulate
there. As soon as the sun rises in the spring it activates the bromine in
these deposits. If it is then carried away with fresh sea salt over the
pack ice, it triggers the complete destruction of the ozone.”
The experimenter John Burrows elaborates: “German researchers from Bremen
and Heidelberg were the first to discover a troposphere ozone hole over
the Antarctic. We are tracking the clouds with GOME and with the
SCIAMACHY-Sensor on Envisat and hope to be able to clarify the many open
questions about the newly discovered cycle of destruction.”
The Earth atmosphere resembles a Swiss cheese. There many ozone holes in
the stratosphere as well as in the troposphere. In the stratosphere
chlorine acts as the aggressive catalytic. The ozone holes over the
Antarctic, the arctic as well as the middle latitudes are clearly
man-made. They are a consequence of the anthropogenic introduction of
CFC’s. In contrast in the troposphere bromine is acting as the catalytic.
So far two ozone holes over the arctic (January until March) and one over
the Antarctic (autumn) have been identified. In these cases it is a
natural phenomenon caused by the destructive effect of bromine which
originates in seawater. There are still many unsolved matters in the
climate who-dunnit. For Sherlock Holmes and Dr. Watson the detail work
comes first. “We are currently investigating with the computer “, says
Paul Crutzen, “Whether reactive halogens – chlorine, bromine und iodine –
can also play a role in ozone chemistry in other regions and seasons.”
Letting Down the Guard or Apocalypse?
Neither nor. The Montreal Protocol to Protect the Ozone Layer in 1987 was
the first decisive step to limit the further damage to the ozone layer in
the stratosphere. There were subsequent steps and Europe played a leading
role. But there are still too many loop holes for state sanctioned
environmental transgressors in the industrial nations themselves.
Ecological inaction has never hurt a politician, as long as regional or
national planning only extends to the next election. Global environmental
protection on the basis of secure scientific data like those Envisat will
provide is therefore one of the most difficult political exercises. At the
same time we have with Envisat, according to John Burrows, “an effective
instrument for monitoring the Montreal and Kyoto treaties…” Furthermore:
“Presumably we will be able to distinguish the anthropogenic and natural
components of the most important substances in the atmosphere.”
How long will we have to live with the ozone hole? For the realistic
optimists, as Paul Crutzen likes to say, the measures are starting to show
an effect. “In the best case scenario the ozone hole will disappear in 40
years. Additional problems could arise, however. We have noticed that the
lower stratosphere is getting cooler.” Crutzen is alluding to the
suspicion that the greenhouse effect in the troposphere could have
disastrous consequences for the processes in the stratosphere.
Measurements show that the water vapor content of the troposphere as well
as the stratosphere is increasing. The extent of the latter is still
unclear. Because of the cooling off in the lower stratosphere which has
also been detected, formation of ice particles could increase, which could
in turn activate the chlorine radicals. In the northern hemisphere and in
the middle latitudes this could enable PSC clouds to form, which need
relatively little chlorine to continue the ozone depletion. In other
words, it could also take much longer, especially since some of the gases
have a very long lifetime of up to 110 year.
The situation with UV radiation in middle Europe is also unclear. Even the
climate experts are poking about in the dark. It will supposedly be at
least 40 to 50 years before the “normal values” of the 60’s of the last
century are reached again. John Burrows also expresses himself cautiously
“For the moment one can’t say anything about trends. For that we need a
run of measurements. We’re waiting for Envisat.”
The Greenhouse Effect
Without the natural greenhouse effect it is certain that we would all be
lost. The global average temperature would drop precipitously 33 degrees
from its current 15° to – 18°. The Earth would congeal into an ice planet
where life would cease to exist. Without the greenhouse effect life on our
planet would not be possible at all. The principle is simple: Trace gases
of the Earth’s envelope of air act like the pane of glass in a greenhouse.
They let through the energy of visible sunlight but hold back the emission
of the thermal radiation. As a consequence the air is heated and the
temperature rises in the atmosphere. Water vapor alone accounts for a rise
of 20.6 degrees. Carbon dioxide accounts for 7.2 degrees and the rest is
taken up by atmospheric trace gases like ozone (2.4 Degrees), nitrogen
dioxide (1.4 Degrees) and methane (0.8 Degrees).
John Burrows believes that “approximately 95% of the warming of the last
100 to 150 years was caused by human activity.” In their basic assessment
the experts are in agreement that it will very likely get warmer. Most of
our contemporaries will be happy about that. But the human induced
greenhouse effect could have far-reaching consequences, like catastrophic
droughts, desertification of agricultural regions, torrential rains and
disastrous flooding of coastal areas and the shifting of climate zones.
The middle and northern latitudes could become substantially warmer and
large areas of the permafrost would thaw. The world’s sea levels, which
have risen 10 to 20 centimeters in the last 100 years, could rise another
30 to 140 centimeters because of melting in glacial regions. This would
have disastrous consequences for coastal regions, like Holland, and for
river delta areas like the Ganges-Brahmaputra. Other stretches of land
would be in danger of flooding.
However a precise prediction about the effects of the increasing
greenhouse effect is not possible at present. Glaciers are sensitive early
warning indicators but until now no clear conclusions can be drawn. A
similar situation exists with the sea levels. In addition the oceans
conceal and delay the effect in that they capture about half of the annual
CO2 produced.
Climate changes proceeds furtively, overlapped with natural variations.
Until the meaningful “signal” has been isolated from the general
background climate “noise”, it could conceivably be too late. The “Core of
the problem is an anthropogenically induced climate change which is
occurring too gradually to be discovered before it is very advanced. And
which can be so far advanced that at the time it is discovered, it is too
late.” In order to confirm or disprove this effect Burrows says, “We need
global models and global measurements over the next 20, 30 or 40 years.
Then we will know which influence is playing which role.”
How we guard against the anthropogenic greenhouse effect is a matter of
extremely diverse opinions. A really efficient, rational use of energy
must be assigned top priority. Energy efficient, high technology must be
developed in order to broadly lower energy consumption. Technologies which
do not release CO2 are required to replace fossil fuels. Worldwide
reforestation is needed to remove more CO2 from the air. And in general
technologies which produce little or no byproducts or operate with closed
cycles which do not burden the environment must be created.
Envisat, the flying climate station
For four decades, weather, Earth reconnaissance and environmental
satellites have been available for large scale synoptic observation. In
1991 the European Space Agency ESA began a very successful Earth
reconnaissance program with ERS 1, followed in 1995 with the world’s best
ozone lookout, ERS 2. With the “Global Ozone Monitoring Experiment” or
GOME for the first time a global ozone map was assembled every three days
which in rapid motion playback impressively visualizes the dramatic extent
of the ozone hole.
Envisat is based on the experience of ERS and is in many categories a more
completive satellite for 3 dimensional monitoring of the environment. The
“most gigantic mission to planet Earth” is a well deserved superlative.
With ENVISAT, ESA has created a behemoth with a system as complex as the
manifold processes of the environmental itself, regularly observing all
important subsidiary processes in the atmosphere, the polar ice region,
the oceans and the land. The exceptional comparability of the data
constitutes at the same time the decisive prerequisite for the recognition
of process dynamics on the Earth. “GOME was pretty successful”, remembers
John Burrows, “but with ENVISAT we can play world wide in the big leagues.
GOME was already advanced with respect to the American system but ENVISAT
represents the absolute top performance for environmental measurements. We
Europeans can depend on our own, independent set of data.”
Three of the ten instruments are for climate research: GOMOS, MIPAS and
SCIAMACHY. “With all three instruments one obtains the most exact data
about ozone distribution and dozens of other trace gases which affect
climate, from ground level to an altitude of 150 kilometers. Taken
together the measurements provide a complex picture of the chemistry of
the atmosphere which helps us to fine tune the models “, explains John
Burrows.
Especially SCIAMACHY, Burrows continues, “will advance us in the research
of air quality. This is a very topical and at the same time urgent theme.
The emissions in the cities lead to ozone formation in an exhaust trail
which affects the surrounding area on a large scale. This is how, when
there is good weather like here in Bremen, the ozone health limits can
easily be exceeded. SCIAMACHY will give us relevant data about the
transport of these pollutants in the air so that we can trace their
movement. That is a trans-continental problem. Part of our air pollution
comes from the US, we transport our pollution to Asia, and the Asians
pollute the US…”
That’s how planetary circulation works. But this example underscores how
compellingly necessary it is to have a broad international collaboration
in science, politics, and application of the data. The ENVISAT-data are at
the disposal of all scientists. 700 international application projects are
already running and the participants can hardly wait to begin the
operational phase.
A change in climate is necessary
To summarize: Prognoses about the future of the world climate are
extremely complex. It will not suffice to identify single parameters and
then to linearly extrapolate them. Models are necessary which with the new
measurement data can be continually compared and modified. The great
uncertainties are in coupled ocean-atmosphere models as well as the
feedback mechanisms of individual parameters. Clouds are a major problem.
Will they strengthen or weaken the expected greenhouse effect? Because of
such uncertainties depending on the model, temperature rises fluctuate
from 1.4 to 5.8 oC with the same starting temperature. “What we need in
environmental research “, warns John Burrows “is long term and continuous
flow of and evaluation of data. Therefore I am concerned that there is no
successor for Envisat planned.”
Burrows concern, a mélange of warning and recommendation, is based on
undeniable facts. The infamous ozone hole was discovered more by accident.
Burrows and Crutzen should know: It could have been much worse. The Paul
Crutzen reminisces in connection with the discovery of the ozone hole
about how very necessary these continuous measurements are: “Since before
1974 no one was concerned about the effects of chlorine and bromine on the
atmosphere, I can only say that we were lucky. This shows that we should
be on our toes about the possible effects of the introduction of new
products in the environment. A permanent surveillance of the composition
of the stratosphere should enjoy high priority for many years to come”. A
lot of overtime is in store for our climate detectives in Mainz and
Bremen. And not just in Mainz and Bremen.
Note to the Editors: all pictures relating to Envisat are available in low
and high resolution under http://www.esa.int. The present information note
is part of a series of articles devoted to the Envisat programme and its
applications.
For further information, please contact :
ESA Communication Division
Media Relations Office
Tel: +33(0)1.53.69.7155
Fax: +33(0)1.53.69.7690
ENVISAT Information Note No. 6
Annex 1
GLOBAL CLIMATE CHANGE: GLOSSARY
Aerosols
A collection of tiny airborne solid or liquid particles, with a typical
size between 0.01 and 10 microns (1 micron is one millionth of a metre).
They stay in the atmosphere for at least several hours. Aerosols may be of
either natural or anthropogenic origin. They may influence climate in two
ways: directly through scattering and absorbing radiation, and indirectly
through acting as condensation nuclei to assist cloud formation or
modifying the optical properties and lifetime of clouds.
Albedo
The fraction of solar radiation reflected by a surface or object, often
expressed as a percentage. Clouds and snow-covered surfaces have a high
albedo; the albedo of soils ranges from high to low; vegetation and oceans
have a low albedo.
Anthropogenic
Resulting from or produced by human beings.
Atmosphere The gaseous envelope surrounding the Earth. The dry atmosphere consists
almost entirely of nitrogen (78.1% by volume) and oxygen (20.9% by
volume), together with other trace gases such as argon (0.93%), carbon
dioxide (0.035%) and ozone. Amounts of water vapour are highly variable
but typically 1% by volume. The atmosphere also contains clouds and
aerosols.
Biomass
The total mass of living organisms in a given area or volume. It includes
dead organic matter.
Biosphere
The part of the Earth system comprising all living organisms – in the
atmosphere, land (terrestrial biosphere), or oceans (marine biosphere) –
as well as dead organic matter.
Carbon cycle
The flow of carbon in various forms (e.g. carbon dioxide) through the
atmosphere, ocean terrestrial biosphere and lithosphere (Earth’s crust and
upper mantle).
Carbon dioxide (CO2)
A naturally occurring gas, also a by-product of burning fossil fuels and
biomass, as well as land use changes and other industrial processes. The
principal anthropogenic greenhouse gas.
Climate
The “average weather” as measured over a long period of time – typically
30 years.
Climate Change
A statistically significant variation in either the mean state of the
climate or in its variability, persisting for an extended period of time,
typically decades or longer.
Climate model
A numerical representation of the climate system which attempts to include
the physical, chemical and biological properties of its components, their
interactions and feedback processes, while accounting for all or some of
its known properties. Such models are used not only to study and simulate
the climate, but for monthly, seasonal and long term predictions.
Cryosphere
The component of the climate system consisting of all snow, ice and
permafrost on or beneath the surface of the Earth.
Ecosystem
A system of interacting, living organisms together with their physical
environment. They may range from the very small scale (e.g. a pond) to the
entire Earth.
El Niño
A warm water current that periodically flows along the coast of Ecuador
and Peru, disrupting the local climate and fishery. This oceanic event is
associated with the Southern Oscillation – a fluctuation in the pattern of
surface air pressure and circulation in the Indian and Pacific Oceans. It
has climatic effects throughout the Pacific and in many other parts of the
world. The opposite of an El Niño event is called La Niña.
Energy balance
A long term balance, averaged over the entire globe, between incoming
solar radiation and outgoing radiation – reflected solar radiation and
infrared radiation emitted by the climate system. Human induced or natural
changes to these inputs and outputs
