Science
Climate change is due to enhancement of the Earth's natural
greenhouse effect, which
is caused by emissions of carbon dioxide and other greenhouse gases that trap heat
in the atmosphere. Rising atmospheric temperatures alter weather
patterns and cause intense rainfall, severe storms and drought, and
disrupt the balance of natural processes (including the carbon
cycle).
What is the greenhouse
effect?
The greenhouse effect is a natural phenomenon that keeps the
Earth within a stable temperature range of 15°C (59°F). Without it,
the average surface temperature of our planet would be -18°C (0°F);
so cold it would be unable to sustain life.
When the sun’s energy warms the Earth’s surface and its
atmosphere, a portion of the heat is absorbed by a delicate balance
of heat-trapping greenhouse gases (among them carbon dioxide and
water vapour), which create an insulating layer and keep the Earth
within its stable temperature range.
Human activities are causing unnatural
enhancement of the Earth’s temperature. Through increased use of
fossil fuels, as well as deforestation and other land-use changes,
we are adding relatively large amounts of greenhouse gases to the
atmosphere and this is having rapid and environmentally-damaging
effects.
While climate change has occurred naturally throughout Earth's
history (fluctuating between ice-ages and warmer periods) human
civilisation has arisen during a period of relative climate
stability and we are not yet equipped to cope with dramatic or
rapid changes in climate.
What are the main greenhouse
gases?
Greenhouse gases come from natural and artificial sources and
can exert their effects in the atmosphere for decades or even
centuries. Properties of the three main greenhouse gases (excluding
water vapour) - carbon dioxide (CO2), Methane (CH4) and
Nitrous oxide (N20) - are shown in the table below:
The effect of greenhouse gas emissions to global
warming
| Gas |
Primary sources (from human activity) |
Contribution to global warming |
Effective lifetime |
Increase in concentration circa 1750-2005 |
Global warming potential |
| CO2 |
Fossil fuel and land use change (20-25%) |
65% |
100yrs |
280-379 parts per million (ppm) |
1 |
| CH4 |
Agriculture |
20% |
12yrs |
715-1774 parts per billion (ppb) |
~25
|
| N20 |
Agriculture |
- |
114yrs |
270-319 ppb |
~300
|
The Scottish
Pollutant Release Inventory provides information on emissions
and waste transfer into the Scottish environment from activities
which are regulated by SEPA. This helps to inform everyone on local
issues, energy use, climate change and promotes
engagement.
The UK’s National Atmospheric Emissions
Inventory (NAEI) compiles estimates of emissions to the atmosphere
from UK sources, such as cars, trucks, power stations and
industrial plants, in order to find ways of reducing their impact
on the environment and our health. The NAEI is funded by Defra, The
National Assembly for Wales, the Scottish Government, and the
Department of Environment for the Northern Ireland Government.
Organic matter also has major role to play in
mediating climatic warming as it is a significant carbon
store. Loss of soil organic matter increases carbon dioxide
emissions and levels of organic carbon in water, as well as
negative effects on other soil functions. Bradley et al.
(2005) stated that Scotland’s soils contain an estimated 2196
million tonnes of soil carbon, to a depth of 100 cm, compared to a
total of 4566 million tonnes for the whole of the UK. Scotland’s
present carbon “store” is estimated as equivalent 200 yrs of
present emissions
Is human activity causing climate change?
Yes! The Intergovernmental Panel on Climate
Change 
(IPCC) has
concluded that:
- warming of the climate system is beyond doubt
- humans are contributing to it
- the last half century has been unusually warm compared to at
least the previous 1300 years
Scientists have simulated the climate's response to natural
causes, such as solar radiation changes and volcanic explosions.
They have found that these kinds of natural events alone could not
have caused the degree of increased climate change in the latter
half of the 20th century. Since pre-industrial times, the
atmospheric concentration of carbon dioxide, which contributes to
climate change, has increased by nearly a third. Over the same
period, atmospheric methane has tripled, mostly from agricultural
activities.
How much warmer could the Earth
get?
The IPCC's Fourth Assessment Report suggests continued
global warming of up to 0.2°C over coming decades. If global
emissions were to be maintained at the level they were in 2000, the
overall increase would be in the range of 0.3 to 0.9ºC or 1.1 to
6.6ºC, depending on a combination of future social and economic
scenarios.
Even if we stopped emitting greenhouse gases immediately, the
climate would not stabilise for many decades because gases already
released into the atmosphere will take decades and even centuries
to disappear. So, while warming rates will slow if we reduce
emissions significantly, global temperatures will not return to
today's averages. The faster and higher the temperature rises, the
greater are the chances of irreversible climate changes.
An increase of a few degrees does not mean pleasantly warmer
temperatures. In the last 10,000 years, the Earth’s average
temperature hasn’t varied by more than 1°C, and even a modest rise
of 1.1° to 1.7°C could have dramatic effects. Indeed, temperatures
only 5° to 9°C cooler than those today prevailed at the end of the
last Ice Age, when large parts of the Northern Hemisphere were
covered by more than 3,000 feet of ice.
What are positive
feedback processes?
Positive feedback is the increase of a system’s natural output.
Global climate change can set-off positive feedback loops in
nature, which trigger ecological and chemical responses and amplify
warming trends. For example, warmer oceans give off more
carbon dioxide and warmer soils decompose faster, releasing
ever-increasing amounts of carbon dioxide and methane. Of course,
it is these greenhouse gases that further exacerbate the problem.
Conversely, negative feedback loops can increase cooling
trends.
What is dangerous climate
change?
There is uncertainty about the link between temperature change
and atmospheric greenhouse gas concentrations. However,
stabilisation in the range of 450 to 550 parts per million (ppm) of
carbon dioxide (CO2) gives us a 50:50 chance of limiting
global temperature increases to between 2 and 3°C. If temperature
rise does exceed 5°C, the Earth’s natural feedback loops (see
above) could become unbalanced, and so prompt abrupt and dangerous
climatic events. This rise is equivalent to the change in average
temperatures from the last ice age to today, but at a rate much
faster than previously recorded.
The Department for Environment Food and Rural Affairs
(Defra) has produced a book called Avoiding Dangerous
Climate Change, which consolidates scientific findings
and gives an account of the most recent developments on:
- critical thresholds and key vulnerabilities of the climate
system
- impacts on human and natural systems
- emission pathways and technological options of meeting
different stabilisation levels of greenhouse gases in the
atmosphere
To read a pdf version of the book, visit Defra's
website:
Is climate change connected to the hole in
the ozone layer?
Climate change and ozone depletion are separate but related
threats. Global warming and the greenhouse effect refer to the
warming of the lower part of the atmosphere (known as the
troposphere), while the ozone hole refers to the loss of ozone in
the upper part of the atmosphere (called the stratosphere).
This is of serious concern because the stratospheric ozone
blocks incoming ultraviolet radiation from the sun, which is
harmful to plants, animals, and humans.
How are they related?
- Trapping heat in the lower part of the atmosphere allows less
heat to escape into space and leads to cooling of the upper part of
the atmosphere. The colder the stratosphere gets, the greater the
destruction of the protective ozone layer.
- Certain ozone-depleting substances, which include gases known
as
halocarbons,
destroy the ozone layer and act as
greenhouse gases.
What needs to be done?
Reducing ozone-depleting gases is crucial to preventing further
destruction of the ozone layer, but eliminating these gases alone
will not prevent climate change. Only efforts to reduce all types
of greenhouse gas emissions will benefit the recovery of the ozone
layer.
Working towards this aim, the Montreal Protocol limits the use
of the most common ozone-depleting substances. Although their
production has largely been phased out in the UK, the long
atmospheric life and prevalence in many products demands continued
monitoring and controls. Visit the Scottish Government's website to
find out more:
What is the best source of
scientific information on climate change?
The Intergovernmental Panel on Climate Change (IPCC) was
established in 1988 by the United Nations Environment Programme and
the World Meteorological Organisation. It assesses scientific,
technical and socio-economic information relevant to understanding
the risks of human-induced climate change, potential impacts and
options for adaptation and mitigation.
Scientists from approximately 100 countries review published and
peer-reviewed scientific information about global climate, how it
changes, what it will mean for people and the environment and what
can be done about it. This information is then used to produce the
IPCC Assessment Reports, which serve as the basis for international
climate negotiations and policy.