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Climate Change: What are the facts?
What I am trying to do
I am very concerned about climate change, and am frustrated that so little seems to be
happening to prevent it. However, I recognize that it is a very technical subject and that
scientific understanding is moving rapidly. Therefore there is a need to present the
current consensus view of the scientific community in a form that is comprehensible to
the intelligent lay reader. Consequently I have gathered together background
information, current scientific knowledge, expert opinion on likely future consequences,
and political responses. Dr Stephan Harrison, climate expert at the University of Oxford
has read this document and he wrote: “I'm happy to say that I agree that the scientific
aspects represent the general consensus of climate scientists.”
What I would like you to do
Please read what I have written below. To keep it as simple as possible, I have put some
of the science and all the references at the end. You don’t need to read them, but please
do if you doubt anything. Please decide whether you agree that there is a compelling
case for immediate and drastic action to reduce climate change, and let me know what
you think in terms of the science and what should be done.
‘Basic’ Facts
Climate change is a complex subject, so it would take hundreds of pages to explain all
the background. However, I hope that the following is sufficient!
The sun’s rays heat the earth. The earth cools by giving off infrared rays. If there is more
heating than cooling, then the earth warms up. However, the earth is very large, so it
takes about 30 to 40 years to heat up.
The atmosphere contains carbon dioxide, methane and nitrous oxide. These gases,
together with water vapour, stop some of the infrared rays escaping from the earth: this
is the natural greenhouse effect. By increasing some of these heat-trapping gases, and
adding new ones, we heat up the earth.
The Lessons from History
The Great Dying, occurred approximately 252 million years ago. It was the Earth's most
severe extinction, with the extinction of up to 96% of all marine species and about 70%
of terrestrial vertebrate species. It is known that huge volcanoes in the Siberian traps
released large quantities of carbon dioxide and sulphur. This lead to a major increase in
temperature, probably triggered other events such as the release of vast quantities of
methane from the sea bed, killing off most of the life on earth.
To and from the Ice Age Very dramatic climate changes occurred at the end of the last
ice age between 20,000 and 10,000 years ago. For instance, during the Younger Dryas
cooling event the temperature in parts of the North Atlantic fell by 80C very quickly:
perhaps within 10 years, and definitely within a 50 years period. Similarly, very dramatic
changes happened at the end of this period when temperatures rose by about 6-80C.
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Around half of the warming seems to have occurred in the space of a single span of 15
years.
What is happening now?
Temperature and CO2 levels Each year we add more than 30 billion tons of carbon
dioxide (CO2) to the air, mainly by burning fossil fuels and cutting down and burning
trees. We also emit other greenhouse gases. The UK emits about 156 million tons of
carbon, and with the other gases, the equivalent total is 199 million tons of carbon.
Global temperature has risen by 0.7oC in 100 years and is rising at about 0.2 oC every
decade.
Glaciers Throughout the world, glaciers are melting. At current rates, there will be no
glaciers left in Africa in 15 years. This melting of mountain glaciers is one reason for
rising sea levels and a clear sign that climate change is real and global in extent.
Greenland ice sheet The edges of the Greenland ice sheet are clearly melting. Unless
there is a catastrophic event, it should take hundreds of years for all this ice to melt.
However, if it does melt, the sea level will rise by over 7 metres.
Extreme Weather There is the possibility that there has been an increase in the
frequency of ‘extreme weather events’ caused by climate change. For example, drought
in Australia, hurricane Katrina, recent floods and the extreme heat wave in Europe in
2003 which killed thousands of people may have been caused by climate change.
Marine acidity Something like half of the extra carbon dioxide caused by human activity
is absorbed by the oceans. So far, this has reduced the impact of climate change, but is
turning the oceans acidic. This seems to be one of the factors causing the death of coral
reefs.
Faster plant growth It is not all bad news. The increased levels of carbon dioxide in the
air may mean that plants can grow a little bit quicker.
Dangers Ahead
By the end of the century, global temperature is expected to rise by between 0.60C if
there are no overall greenhouse gas emissions (not going to happen!!) and 4.00C
(perhaps as much as 6.40C ) with fossil fuel intensive economic growth.
Forests As the climate changes, the habitats of plants (and animals) will change. Most
places are getting hotter, some places will become drier, and others will become wetter.
Of particular concern is the expert opinion that a rise of 2 or 30C might kill the Amazon
rainforest and the broad-leaved forests of China. Most worrying, a 40C rise is predicted
to cause the extinction of more than 40% of all species.
Marine Life The increasing acidity of the oceans is making it increasingly difficult for
marine life. Thus, there is a chance that in the near future, a large proportion of the
world’s marine life will die. This includes plankton, seaweeds and fish.
Methane Rotting plants and animals naturally give off methane. Much of this methane is
trapped in permafrost and under the oceans. Permafrost covers about half of Canada
and half of Russia and is up to 800 metres deep. As the earth warms, the permafrost will
begin to melt, and the oceans will warm. This will release the trapped methane into the
air and the melting of permafrost ice will increase sea levels.
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Sea Level As the earth warms, snow and ice melts, sending water into the oceans. In
addition, water expands as it warms. These two effects have already lead to the sea
level rising; but probably only by about 0.5 m so far. However, the danger is that
significant portions of the Greenland or Antarctica icesheets may melt leading to
massive rises in sea level. Greenland has enough ice to produce a 7m rise in sea level,
and Antarctica has enough ice for a 35m rise. Clearly even a small percentage of these
quantities would lead to the drowning of many of the earth’s major cities and a large
proportion of agricultural land. If this happened, then it would be inevitable that millions
of people would die as a result.
Antarctic A rise in sea level and a small temperature rise could be enough to break up
the marine ice shelves in Antarctica. Removing this ‘barrier’ to the land-based ice may
allow vast quantities of ice from the continental interior to slip towards the sea. Once this
happens, friction can melt the ice at the bottom allowing it to slide even faster, causing
an ‘ice armada’. This has happened in the past, so it is quite possible it will happen
again. An ice armada could cause sea level to rise by several metres in a very short
time. This is a very serious threat as it could easily drown much of UK including London,
costal towns and the rich agricultural fens in East Anglia and Lincolnshire.
The Run-away Greenhouse
As the earth warms, its response will change, for example:
Snow and ice reflect sunlight, so when they melt, more sunlight is absorbed by
the earth, heating it faster.
When forests die, they will give out large quantities of carbon dioxide. This leads
to a further increase in temperature as carbon dioxide is a greenhouse gas. In
addition, there will then be fewer plants absorbing carbon dioxide, so the
problems will rapidly increase.
Also, if marine life dies, then it will stop being able to absorb carbon dioxide; thus
speeding up the greenhouse effect.
Similarly, there is a lot of carbon in soil. If the plant cover disappears, then this
carbon, too, will be released into the air as carbon dioxide.
Hotter water is less good at absorbing carbon dioxide, so as the oceans warm
they may start releasing carbon dioxide back into the air, rather than absorbing it.
Methane is around 20 times stronger as a greenhouse gas than carbon dioxide,
so methane released from permafrost, from under the oceans and from other
land may rapidly increase the earth’s temperature.
These five effects create a vicious circle: a warmer earth leads to fewer plants, less
carbon dioxide in the oceans, and the release of methane. All these factors increase the
greenhouse effect and so create a warmer earth that then leads onto even fewer plants,
more release of methane…etc. This is one way in which a run-away greenhouse effect
could start. Most scientists agree that once it starts, it will be impossible to stop. This will
lead to massive rises in sea level, drowning much of the land, including major cities and
farming land. In addition, the widespread destruction of the biosphere will mean that
many crops will not grow, there will be very widespread famine and quite possibly the
collapse of our civilisation.
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When??
Some scientists believe it is already too late and that some of the vicious circles
described above are already happening. Others believe there may be a few more
decades until it is too late.
Urgent, sustained and immediate action is the best decision for the following reasons:
•
The earth takes 30 to 40 years to respond to any changes in greenhouse gases.
So even if we stop all fossil fuel based transport, stop all heating using coal, oil
and gas, and stop producing electricity from fossil fuels, then the earth will still
carry on heating for 30 to 50 years becoming about 0.6oC hotter. Clearly no-one
intends to take such drastic action.
•
As more countries develop and become richer, there are more people adopting a
Western, energy-rich life-style. Currently, this is particularly true of China and
India. Consequently, projections are for massive and sustained increase in use of
fossil fuels. Therefore, the earth’s leaders are ‘anticipating’ a 62 percent increase
in emissions of carbon dioxide in the next 25 years.
•
As explained above, once the run-away greenhouse effect starts, the vicious
circles increasing the earth’s temperature will make it impossible to stop.
Political Action
Clearly we have a system in which the people in rich countries are using far too much
fossil fuel for industry, transport, heating and food. People in poorer countries are
aspiring to our way of life, and are trying to dramatically increase their use of fossil fuels.
However, this pursuit of material wealth will certainly lead to devastating climate change
that will destroy all that we are trying to achieve. Therefore it is madness to continue on
this path. It is not known whether we are too late to stop devastating climate change, or
whether there are a few more years before we reach the point of no return. However,
current global emissions are set to rise relentlessly, despite the clear message from
climate change researchers that this is endangering the whole of human civilisation. The
only sensible approach is to accept that the best available scientific evidence is
that we must make dramatic changes to our generation and use of energy. The
sooner we make these changes, the less disruptive it will be for society and the
better our chance of a better world.
I have great faith in the ability of industries to adapt given the right economic incentives. I
also have great faith in ordinary people to ‘do their bit’, if there is a clear message that
this is the best way for us to maintain a high quality of life. So the major problem is to
convince the politicians that drastic action is needed now. Politicians are slowly
acknowledging that threat, but have consistently adopted policies that would do too little,
too late and promote economic growth that increases carbon emissions.
The House of Commons Environmental Audit Committee has damned the government’s
stance, despite the fact that 10 out of 16 of its members are Labour MPs. In their report
also published in March 2005, they wrote that, “Governments must act as a matter of
urgency and on an unprecedented scale: a Marshall plan for climate change is now
required.” And they reported that, “Sir David King has suggested that the UK’s 60%
carbon reduction target which the UK Government has set for 2050 may need to be
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increased to 80%.” And they concluded that, “The challenge of climate change is so
great that action is required on all fronts if we are to achieve the scale of emission
reductions required … it is simply not credible to suggest that the scale of the reductions
which are required can possibly be achieved without significant behavioural change. In
focussing on science and technology, the Government is creating the appearance of
activity around the problem of Climate Change whilst evading the harder national and
international political decisions which must be made if there is to be any solution.”
The Global Commons Institute has proposed the Contraction and Convergence (C&C)
model to combat climate change. In this model, the carbon dioxide emissions of all
countries are reduced (contraction) and converge to an equal amount on an annual per
capital basis. This is generally seen as the only fair approach, and is becoming more
accepted. However, despite many politicians saying that they support contraction and
convergence, their policies show that they are not committed to its success. It is
interesting that the Archbishop of Canterbury said: “C&C thinking appears utopian only if
we refuse to contemplate the alternatives honestly.”
Simple maths shows that an 80% reduction by 2050 requires a 2 to 3% cut in carbon
dioxide emissions per year. Anything less is disaster and many people are saying this
will be too little. In addition, global action is required to increase the ability of the
biosphere to absorb carbon dioxide (such as growing more forests).
My request to you
Congratulations for reading this to the end! You will have gathered that I believe climate
change threatens:
the extinction of most species on earth;
to kill most of the human population; and,
to destroy our current civilisation.
I would be delighted if you told me your honest opinion. If you don’t believe me, please
point out the holes in my argument or where there are difficulties in understanding.
Many people don’t believe that the threat of climate change is as serious as I’ve
indicated: perhaps they’ve read something in the paper or seen it on TV. However, the
scientific evidence and the consensus of climate change scientists are overwhelming.
Please contact me or go to http://gristmill.grist.org/skeptics if you would like answers to
arguments from sceptics.
Very many thanks,
Ian Davison [email protected]
Updated 2nd October 2007.
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Further information
You don’t need to read this, but below is scientific information and references
under the same headings as before.
What I am trying to do
Dr Stephan Harrison’s website is http://www.geog.ox.ac.uk/staff/sharrison.php .
Basic Science
Incoming short-wave radiation (mainly visible light, ultraviolet light and short-wave
infrared rays) from the sun heats up the earth. The earth cools, largely by giving off longwave infrared radiation. When these two processes are exactly balanced, then the earth
stays at the same temperature.
Radiative forcing is a measure of the influence a factor has in altering the balance of
incoming and outgoing energy in the Earth-atmosphere system, and is an index of the
importance of the factor as a potential climate change mechanism. It is expressed in
Watts per square metre orWm−2 (see page 5, IPCC 2001 reference given below).
Therefore the heating effect is stronger when the radiative forcing is greater.
The power of the sun’s rays is 1370 watts per metre squared (Wm-2) when it reaches the
earth. You will see in the table below, that the radiative forcing from carbon dioxide is
roughly 1.5 Wm-2. This is tiny compared with the power of the sun; but this small effect
over many years is gradually warming the earth.
The Great Dying
More formally this is called the Permian- Triassic extinction event. The entire extinction
probably only lasted 80,000 years and showed distinctive phases in the plant and animal
fossils they contained. The extinction appeared to kill land and marine life selectively at
different times. The increase in carbon-12 over time has led to the suggestion that the
increased temperatures also released huge volumes of methane gas from the sea bed.
(See http://en.wikipedia.org/wiki/Permian_extinction.)
Also see Peter Ward, Impact from the deep. Scientific American, 295, (4) 42-49 which
suggests that for mass extinction, the greenhouse gases cause climate change that
leads to release of poisonous gases and destruction of the ozone layer.
To and from the Ice Age
The theory that methane was released is according to analyses of the Greenland ice
core record (Taylor et al., 1997 and see Alley, et al. 1993. Abrupt increase in Greenland
snow accumulation at the end of the Younger Dryas event. Nature, 362, 527-529.
What is happening now?
The next two figures are taken from pages 3 and 4 of Climate Change 2007: The
Physical Science Basis Summary for Policymakers Contribution of Working Group I to
the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
(http://ipcc-wg1.ucar.edu/ and http://www.ipcc.ch/WG1_SPM_17Apr07.pdf )
The table below shows the way that carbon dioxide, methane and nitrous oxide levels
have increased since the start of the industrial revolution. At the moment, the amount of
CO2 in the atmosphere is about 380 parts per million and rising by about 1.9 part per
million each year.
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FIGURE SPM-1. Atmospheric
concentrations of carbon
dioxide, methane and nitrous
oxide over the last 10,000 years
(large panels) and since 1750
(inset panels). Measurements
are shown from ice cores
(symbols with different colours
for different studies) and
atmospheric samples (red lines).
The corresponding radiative
forcings are shown on the right
hand axes of the large panels.
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FIGURE SPM-2. Global-average radiative forcing (RF) estimates and ranges in 2005 for
anthropogenic carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and other
important agents and mechanisms, together with the typical geographical extent (spatial
scale) of the forcing and the assessed level of scientific understanding (LOSU). The net
anthropogenic radiative forcing and its range are also shown. These require summing
asymmetric uncertainty estimates from the component terms, and cannot be obtained by
simple addition. Additional forcing factors not included here are considered to have a
very low LOSU. Volcanic aerosols contribute an additional natural forcing but are not
included in this figure due to their episodic nature. Range for linear contrails does not
include other possible effects of aviation on cloudiness.
Temperature and CO2 levels
“The global atmospheric concentration of carbon dioxide has increased from a preindustrial value of about 280 ppm to 379 ppm3 in 2005. The atmospheric concentration
of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years
(180 to 300 ppm) as determined from ice cores. The annual carbon dioxide
concentration growth-rate was larger during the last 10 years (1995 – 2005 average: 1.9
ppm per year), than it has been since the beginning of continuous direct atmospheric
measurements” page 2 of IPCC physical basis report (reference given above).
Predicted temperature rises are given in the same report.
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http://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_emissions for
emissions per country
DEFRA publishes figures for the UK emissions
(http://www.defra.gov.uk/environment/statistics/globatmos/index.htm ). In 1997, the UK
emitted 548 million tons of carbon dioxide (MtCO2) and the equivalent of 706 MtCO2
including other green house gases such as methane and nitrous oxide. By 2005, these
figures were 554 for carbon dioxide (i.e. gone up) and 656 total (i.e. gone down). So,
overall emissions are falling slowly especially due to less methane from landfill sites, but
there’s been no effective action to cut CO2 emissions.
Glaciers
Rignot et al. (2003 Science) provide evidence that the sea level is rising, partly due to
the melting of temperate glaciers.
Extreme Weather
The extreme heat wave in Europe in 2003 which killed thousands of people is likely to be
a product of climate change (Stott et al Nature 2004). In recent decades, there has
certainly been a huge increase in the number and severity of El Nino years. The science
behind this is complex, but seems to be linked to climate change.
Faster plant growth and dangers ahead
Although there is evidence of faster plant growth, recent research shows that plant
growth in a warmer world (even with enhanced carbon dioxide levels) may be restricted
because of changes in nitrogen levels and water supply.
At the moment, the biggest impact (in climate terms) is that forests in the northern
hemisphere are growing slightly faster, thus absorbing a little of the excess carbon
dioxide. But these are also drying out, so the good news may not last for long. There
are many detailed predictions in Climate Change 2007: Impacts, Adaptation and
Vulnerability Working Group II Contribution to the Intergovernmental Panel on Climate
Change Fourth Assessment Report (http://www.ipcc.ch/SPM13apr07.pdf ) see figure
below for a summary.
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Table SPM-1. Illustrative examples of global impacts projected for climate changes (and
sea-level and atmospheric carbon dioxide where relevant) associated with different
amounts of increase in global average surface temperature in the 21st century [T20.7].
The black lines link impacts, dotted arrows indicate impacts continuing with increasing
temperature. Entries are placed so that the left hand side of text indicates approximate
onset of a given impact. Quantitative entries for water scarcity and flooding represent the
additional impacts of climate change relative to the conditions projected across the
range of Special Report on Scenarios (SRES) scenarios A1FI, A2, B1 and B2 (see
Endbox 3). Adaptation to climate change is not included in these estimations. All entries
are from published studies recorded in the chapters of the Assessment. Sources are
given in the right hand column of the Table. Confidence levels for all statements are
high.
Sea Level
As the earth warms, snow and ice melts, sending water into the oceans. In addition,
water expands as it warms. These two effects have already lead to the sea level rising;
but probably only by about 0.5 m so far. However, the danger is that significant portions
of the Greenland or Antarctica icesheets may melt leading to massive rises in sea level.
Greenland has enough ice to produce a 7m rise in sea level, and Antarctica has enough
ice for a 35m rise. Clearly even a small percentage of these quantities would lead to the
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drowning of many of the earth’s major cities and a large proportion of agricultural land. If
this happened, then it would be inevitable that millions of people would die as a result.
Antarctic
The consensus view in 2001 was that the Antarctic ice-sheets were probably stable, and
would only melt very slowly (i.e. over thousands of years). However, this view has
changed in the last few years. Scientists now speak of possible destabilisation. The
contribution that rapid thinning of the Antarctic ice sheet is making to global sea-level
rise is a cause for concern according to Director of British Antarctic Survey (BAS),
Professor Chris Rapley. He said, "Satellite measurements tell us that a significant part of
the West Antarctic ice sheet in this area is thinning fast enough to make a significant
contribution to sea level rise… There is real cause for concern." Feb 2005
http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=56
The Run-away Greenhouse
Methane is around 20 times stronger as a greenhouse gas than carbon dioxide, so
methane released from permafrost, from under the oceans and from other land may
rapidly increase the earth’s temperature. See Bruce Buffett and David Archer, 2004
‘Global inventory of methane clathrate: sensitivity to changes in the deep ocean’ Earth
and Planetary Science Letters 227 185– 199.
When??
CO2 in the atmosphere is rising fast. “According to Dr Tans, one significant finding is that
the annual rate at which the CO2 is rising has itself increased. The growth rate over the
past decade was about twice as fast as that found in the 1960s” (see
http://news.bbc.co.uk/1/hi/sci/tech/4395817.stm ).
It is possible that we are already starting the run-away greenhouse effect; perhaps
because the oceans are no longer absorbing as much CO2. However, it is not clear
when the other 4 vicious circles mentioned above will start to have an impact. The expert
judgement of Hansen et al is that “a CO2 level exceeding 450 ppm is almost surely
dangerous, and the ceiling may be even lower… Have we already passed a “tipping
point” such that it is now impossible to avoid “dangerous” climate change…? In our
estimation, we must be close to such a point, but we may not have passed it yet.”
Hansen et al (2007) ‘Dangerous human-made interference with climate: a GISS modelE
study’ Atmospheric Chemistry and Physics 7, 2287–2312 http://www.atmos-chemphys.net/7/2287/2007/acp-7-2287-2007.html
The 2004 World Energy Outlook of the International Energy Agency calculates that in
the next 25 years, global emissions of CO2 are likely to increase by 62 per cent.
Political Action
The House of Commons Environmental Audit Committee report can be found at:
http://www.gci.org.uk/briefings/EAC_Final_C&C.pdf
The global commons institute website is at: http://www.gci.org.uk/
See http://www.gci.org.uk/speeches/Williams.pdf for the 2004 the Archbishop of
Canterbury quote.
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