Download Introduction: the evidence for anthropogenic climate change

Introduction: the evidence for
anthropogenic climate change
Presented by
James Reeler
UWC
Climate variation
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All manner of human and natural
activities are affected by weather
and climate
WEATHER is the day to day
effect of natural conditions.
CLIMATE refers to an averaging
of these conditions over a
longer period, obtaining a
general picture of trends in
conditions over time.
Both systems are highly variable.
Climate is influenced on varying time scales by factors such as
fluctuations in solar output, the Earth’s orbit, changes in vegetation
cover and in the gaseous composition of the atmosphere (IPCC, 2001).
This short-term variation is termed climate variability, or CLIMATE
VARIATION.
Climate change
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A long term trend in climatic conditions
away from the established conditions is
termed CLIMATE CHANGE.
The earth has always experienced climate
change due to natural variations in
insolation and atmospheric conditions– it
is not a new process.
Orogeny, which is the development of
new surface features on a geological time
scale, can affect the climate gradually.
The most recent ice age ended 10 000
years ago, and what we have been
experiencing in recent history may be
termed a “climatic optimum”
It is telling that agriculture only arose as a
human adaptation strategy within the last
few thousand years, corresponding to
optimal growth conditions for agricultural
crops.
Source: Canadian Institute
for Climate Studies
What are we looking for?
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Source: IPCC online talks
Changing climatic variables
could be expressed in different
ways, depending on how the
climate is transformed.
A change in mean temperature
would mean we would see more
extreme heat and hot weather
events.
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A transformation in variance of temperature would give a broader
spread, resulting in more extremes of both heat and cold.
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If there were a change in both mean and variance of temperature,
whilst we would see more extreme heat and warm weather, we might
still observe extremes of cold weather.
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This type of change might therefore hide the signal, since certain
areas would be unchanged. Only after extensive observation would
the trend be clear. This may be what has happened in recent history
Sources of data - instrumental
• Instrumental measurement of climate variables is an
important data source, although we only have true
records for a short historical period.
• Using standard instruments, we record:
• Temperature
• Rainfall
• Wind
• Humidity
• Atmospheric aerosol and gas concentrations
• These standard variables allow measurement of
change in the earth’s systems.
Temperature
• Temperature is an essential indicator variable, because it
provides us with a direct measurement of the energy in
the earth’s atmospheric system.
• Temperature records date from the middle of the 19th
century.
• Surface air temperature is usually measured at weather
stations by means of mercury or alcohol thermometers.
• However, much recent work has been done to allow
measurement of the temperature of other atmospheric
levels, using the TIROS-N series of satellites.
• These atmospheric temperature records start in 1958
(conventional radiosonde network)(Angell, 1988) and 1979
(microwave-sounding unit) (Spencer & Christy, 1990)
respectively.
Palaeoclimate reconstruction from proxy data
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In order to obtain data prior to the advent of modern measuring devices,
climatologists resort to using proxy data from a variety of sources.
Sources of proxy data include:
- Glaciological (ice cores)
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Oxygen isotopes
Trace elements and microparticle concentrations
Physical properties
Geological
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Sediments
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Sedimentary rocks
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Facies analysis
Fossil/microfossil analysis
Mineral analysis
Isotope geochemistry
Biological
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Marine – organic/inorganic sediments
Terrestrial – glacial / periglacial/ aeolian/ lacustrine
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Tree rings (dendroclimatology)
Pollen species/abundances
Insects
Historical
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Historical meteorological records
Parameteorological records (environmental indicators)
Phenological records (biological indicators)
Palaeoclimatological time scale
Proxy
Time period before present (years)
109 108 107 106 105 104
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Historical
Tree rings, pollen
Ice cores
Glacial deposits
Marine organic
sediments
Inorganic sediments
Sedimentary rocks
Decreasing
resolution
(and
accuracy)
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Proxy data sources: Ice cores
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Data from ice cores is extracted in a
number of ways.
Oxygen isotopic analysis gives an idea of
the temperature at which the ice was
deposited (since O18 has a higher vapour
pressure, it is preferentially deposited)..
In warmer conditions, more O18 will be
found in the polar ice (Craig, 1961 ; Morgan,
1982).
Atmospheric gas concentrations can be
extracted from bubbles formed by the
closing off of air pores as firn turns to ice.
(Raynaud & Lorius, 1973) .
Physical variations in ice structure such
as crystal size, incidence of melts and
number/structure of bubbles give an idea
of temperature and frequency of melt
periods or deposition (Langway, 1970;
Koerner, 1977).
Proxy data sources: Dendroclimatology
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The pattern of growth of trees is
laid down within their structure,
providing a high-resolution
(annual) picture of climatic
variables in the Holocene.
Much can be deduced from
growth bands – the thickness
corresponds to the favourability
of climatic conditions (light,
temperature, rainfall, windspeed)
(Bradley,1985; Fritts, 1976).
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The density of the bands says
much about the growing season
(latewood is much denser than
earlywood) (Schweingruber et al.,
1978).
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Isotopic analysis of the bands can also give us information about the
climatic conditions. (Epstein et al., 1976).
By studying a number of trees in an area of a similar age, a statistically
sound analysis of conditions can be obtained.
Proxy data sources: Oceanic sediments
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Preferential uptake of O18 under cool
conditions by fossilized plankton
allows analysis of the temperature of
deposition by isotopic analysis. (Urey,
1948).
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Species assemblages show variation
in the number of warm- and cold-water
plankton species. (Williams & Johnson,
1975)
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Morphological variations are expressed by a number of species in
response to climatic variables. (Kennett,1976).
The content of terrigeneous material in sediments corresponds to
continental weathering. Consequently, the purity of the calcareous
ooze gives a strong indication of the extent of weathering. (Hays &
Perruzza,1972).
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The chemical and physical processes affecting the inorganic
sediments prior to deposition correspond to particular climate
regimes. (Kolla et al., 1979).
Proxy data sources: Other
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Glacial moraines give a rough picture
of glacial advances and retreats, but
successive movements which erase
each other, as well as difficulties in
dating moraines, limit the application.
Lacustrine (lake) size variation,
especially in arid areas, can be
significant, so stratigraphic and
microfossil analysis can give some
indication of climate variation.
Pollen accumulates on all surfaces, and is useful for palaeoclimatic
deduction. However, the many difficulties associated with analysis
mean that only qualititative comparisons are feasible.
Sedimentary rocks can provide data through facies analysis (rock
types), assessment of fossils and microfossils, and analysis of
sediment grain size/rate of deposition. However, the resolution of
these data is very low (thousands of years).
The role of climate models
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Once historical and palaeoclimatological data have been
gathered, we have some idea of:
- How the climate has changed in the past
- What atmospheric and biological conditions were
associated with this change
This allows us to build and test models of the interaction
of climatic variables
These models allow us some capacity to then establish
how a given change in certain factors will affect future
climate.
This becomes the basis for assessment of the current
state of the environment
We will go into this in more detail in chapter 2.
Evidence for change
• So, what evidence is there for anthropogenic
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change?
By comparing current data and measurements with
historical and palaeclimatological data, we have
obtained a good picture of the climate over the last
several thousand years.
It is clear that there has been a significant
transformation of the climate over the last hundred
years, and that the rate of change is increasing.
Signal analysis and modelling has proved that this
change cannot be attributed to processes other than
human interaction with the environment.
Thermal indicators: Glacial melting
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Glacial retreat over a 98year period in Glacier
National Park , USA.
Glacier National Park
Archives/F.E. Mathes (1900),
USGS/L. McKeon (1998)
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Decrease
in cumulative
net balance
The change in size
of glaciers
is measured
by their
over
periodgain/loss
1975- 2003of mass at
mass balance: the
netthe
annual
the glacier surface per unit surface area.
This is useful because it measures the contribution
of glacial melt to sea level rise.
Almost all glaciers have been shown to be retreating.
(IAHS (ICSI)/UNEP/UNESCO, 1998)
Some glaciers in Norway and New Zealand are
advancing, but this is because of increased
precipitation due to warmer weather.
Exposure of radiocarbon-dated ancient remains in
high saddles in the Alps shows recession is reaching
levels not seen for thousands of years
This ice has not melted for thousands of years,
hence the finding of the 5000 year-old Oetzal “ice
man”. (IPCC, 2004)
Source: World Glacier Monitoring Service
Thermal indicators: Sea ice
• Comprehensive Antarctic sea ice records
date from the 1970s, although there is
considerable data prior to this point for
the Arctic. (Parkinson, 2000).
• A considerable decrease in sea ice
thickness over the 1978-1996 period has
been observed (Parkinson et al., 1999).
• Satellite data has shown a considerable
decrease in the extent of sea ice.
• This is particularly evident in the collapse
of the Larsen B ice shelf in 2002.
• Four other major ice shelves have
retreated (Vaughan and Doake, 1996).
• Sea ice melt does not contribute to sealevel rise, since it is already in the ocean.
Thermal indicators: permafrost
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About 25% of the Northern Hemisphere
landmass is under permafrost , including
much of Canada, China, Russia and
Alaska (Brown et al., 1997).
Significant portions of this area are now
undergoing melting as a result of raised
temperatures.
This is seen through the sudden
appearance of potholes of considerable
size and the draining of many lakes as
their frozen base is removed.
However, direct measurement of the
melting of permafrost has been gathered
over the last twenty years in many
regions of the world (Gravis et al., 1988;
Weller and Anderson, 1998; Romanovsky and
Osterkamp, 1999)
A pothole formed by melting
permafrost. You can see still frozen ice
at the back of the hole.
Source: Romanovsky, Fairbanks
Alaska.
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Onset, magnitude and extent of
permafrost melting varies from area to
area.
Thermal indicators: Sea level change
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Sea level has risen by an average
of 15 cm over the last century (IPCC
2001).
Melting of sea ice does not
increase the level of the oceans.
However, as the ice Antarctic ice
sheet retreats, it is increasing polar
glaciers’ access to the ocean.
SOURCE: IPCC website
As their flow increases under
gravity, they will likely contribute more to the rise in sea level. The
extent and rate of this influx is a subject of much research.
In addition to the increasing amount of water flowing into the
oceans, the sea level is likely to rise due to thermal expansion.
Simulations predict that ultimate levels could reach as much as
an additional 2m at equilibrium.
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Thermal indicators: Sea temperatures
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Sea temperatures have been
gradually increasing worldwide.
Measurements in the 19th century
were somewhat inaccurate, but
this is taken into account through
a correction factor.
Immediate effects of this will
include a change in the capacity
Source: UK Meterological Office
of seawater to absorb CO2.
Source: IPCC
Long term concerns of such a trend include the shutting down or
movement of oceanic currents such as the “conveyor belt”, ironically
reducing air temperature in areas of atmospheric heat release .
More importantly, the deep saline currents provide many nutrients for
surface ecosystems fed by plankton. A reduction in oceanic plankton
will limit another important carbon sink, since many species have
carbonate shells. It may also cause a crash in oceanic biodiversity.
Is oceanic circulation changing?
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The El Niño Southern Oscillation is
a current system that is the primary
global mode of variation on the 2 to
7 year time interval, typified by a
change in SST anomaly. (IPCC, 2001).
ENSO is associated with extreme
climatic events .
Multiproxy reconstruction of ENSO
suggests recent extremes are
outside the norms of historic
conditions.
Source: IPCC Third Assessment Report
The 1990s in particular show trends outside the norms of previous
decades, including reduced variability (more El Niño events with reduced
occurrence of the corollary cool La Niña) (Goddard and Graham, 1997).
Similar statistical anomalies have been observed in both the North
Atlantic Oscillation and the North Pacific Oscillation.
These anomalies may be part of a larger variation, or may be part of the
natural cycle – it is too early to determine for certain at this stage.
The greenhouse effect
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Source: ARIC
To some extent, life on earth is
contingent on the greenhouse effect –
without it the earth’s surface
temperature would be considerably
below the freezing point of water.
Certain gases are opaque at infra-red
light frequencies. These include
methane, water vapour, nitrous oxides,
ozone, and most importantly, CO2.
Some short wave solar radiation is converted to long wave infra red at the
earth’s surface. This is then absorbed by greenhouse gases, raising the
atmospheric temperature.
 As the proportion of greenhouse gases in the atmosphere increases, so
does the potential for absorption of radiation, effectively raising the
temperature.
 This effect, and the dangers of increased carbon dioxide emissions was
outlined by Svante Arrhenius over a century ago! (Arrhenius, 1896).
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Climate change forcings
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The effect of various factors on the
climate are expressed as a forcing
value (ie: to what extent they force
global warming)
The forcing value is measured in Wm-2
(the increase in effective energy
caused per square metre).
Forcings are discussed in more detail
in the next chapter, on GCMs, but for
now it is important to understand that
there are many sources of climate
forcing.
However, human activity has
introduced significant radiative forcing
to the atmosphere through various
factors, and these will be touched
upon in the next couple of slides.
Source: Mauna Loa Observatory
Greenhouse gases: methane
Since(CH4),
the beginning
of the industrial revolution,
is
and most
particularly in the last century with the
produced
by domestic
widespread
use of the internal combustion
animals
in large quantities.
engine, atmospheric concentrations of
Also produced by all
greenhouse
gases have climbed massively.
anaerobic
decomposition
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Methane
(notably in landfills,
hydroelectric dams and
rice paddies). (Prather et
al.,1995).
Source: IPCC Third Assessment Report
increase relative to 1765 (Wm-2):
1900 1960 1970 1980 1990
0.1
0.24
0.30
0.36
0.42
Forcing
Greenhouse gases: nitrous oxide
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Nitrous oxide (N2O) is
naturally produced by
biological functions in the
soil and oceans.
Anthropogenic sources
include industrial
combustion, vehicle
exhausts, biomass
burning and the use of
Source: IPCC Third Assessment Report
chemical fertilisers.
Forcing increase relative to 1765 (Wm-2):
1900 1960 1970 1980 1990
0.027 0.045 0.054 0.068 0.10
Greenhouse gases: carbon dioxide
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Carbon dioxide is emitted
by all combustion,
particularly fossil fuels
used for engine fuels and
energy generation.
Burning of forests also
emits CO2, as well as
reducing their capacity
for carbon sequestration.
Source: IPCC Third Assessment Report
At this stage CO2 is the largest anthropogenic contribution to
climatic forcing. Levels are higher than at any time in the past
450 000 years.
Forcing increase relative to 1765 (Wm-2):
1900 1960 1970 1980 1990
0.37
0.79
0.96
1.20
1.50
Greenhouse gases: others
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Ozone plays an important role in reducing shortwave radiation
influx by absorbing primarily ultraviolet light in the upper
atmosphere (Chapman, 1930). However, as a pollutant in the
lower atmosphere it also acts as a greenhouse gas.
The catalytic action of nitrous oxides, halocarbons and hydroxl
ions (OH-) in the stratosphere catalytically destroys large
quantities of ozone, thereby increasing solar radiation.
Halocarbons (CFCs and HCFCs), apart from destroying ozone
in the upper atmosphere, are very strong greenhouse gases
(thousands of times stronger than CO2) (IPCC, 1990).
Furthermore, they are highly stable, taking decades to
centuries to break down.
Forcing increase relative to 1765 (Wm-2) for CFC-11 and CFC-12
combined:
1900 1960 1970 1980 1990
0.0
0.012 0.048 0.111 0.202
Aerosols
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Aerosols are small particles dispersed in the air (Kemp, 1994),
and include dust, water, soot, sea crystals, and many others.
Aerosols typically generate a cooling effect on the atmosphere
by either acting as seeds for cloud formation, or by directly
reflecting solar radiation.
Although natural causes still generate significantly more
aerosols than anthropogenic, there is some concern that the
high levels of aerosol emission in the northern hemisphere
(particularly where there is large amounts of burning such as
the East, or dirty power generation) might be masking the
actual effects of climate change.
This cooling effect is a very short term effect in comparison to
other anthropogenic radiative forcings, and consequently
climate change may paradoxically be accelerated to some
extent by reduced emissions.
Sulphates and nitrates
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Data from the Greenland ice
sheet shows a dramatic
increase in non-sea nitrate
and sulphate concentrations
since 1900 due to human
activities.
These compounds are
released through
combustion of fossil fuels,
and are primary components
of acid rain
Ironically, these aerosols
may be offsetting the global
warming effects of CO2.
Click to enlarge.
Data from Mayewski et al, University of
New Hampshire.
See Mayewski et al (1986, 1990)
Thermal indicators: global air temperature
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The mean global
temperature has risen
considerably in the past
century (0.6°C ± 0.2°C)
(IPCC, 2001).
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The 1990s were the warmest decade ever recorded .
Furthermore, proxy records indicate that temperatures have not
reached current levels for at least the past thousand years.
In fact, proxy records indicate that the last time global
temperature reached levels like the current conditions were at
the peak of the last interglacial period, 124 000 years ago.
Note that proxy records for recent history corroborate
instrumental temperature assessments. This indicates the
accuracy of proxy interpretation methods.
Changes in precipitation
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Globally, an increase in
precipitation over land of
approximately 2% has been
observed over the last
century (Jones and Hulme, 1996;
Hulme et al., 1998).
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However, this effect is
localized, and such areas as
the Sahel and sub-Saharan
Africa have actually seen a
decrease in rainfall.
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Precipitation over the ocean can only properly be estimated from
satellite observations, and as such, full records have only been
available since 1987.
Current indications are that oceanic precipitation has increased as
well, but it is too early to say with statistical certainty.
There may be a trend towards more intense rainfall events – whilst
much of sub-Saharan Africa is getting less rain, it is also getting it in
short bursts, rather than spread evenly over a season.
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Climate change indicators: extreme weather
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Tropical cyclones are associated with
high winds and extreme rainfall, and
have become high profile events of late.
However, an analysis of moderate and
strong cyclones (≤ 980 hPa) shows no
statistically significant trend.
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similar analysis of extra-tropical
cyclones reveals a significant
increase in the latter half of the
20th century.
 It is unclear at this juncture
whether this is part of a multidecadal variation or a significant
long-term trend.
Interannual variability in the number of major hurricanes and
the long-term average across the North Atlantic (Landsea et al.,
1999).
Conclusions?
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The international scientific community
is now in firm agreement that global
climate change is an established fact.
To some extent our understanding of
future trends in the climate is
dependent on the accuracy of the
model we use to describe the
processes, as will be described in the
next chapter.
However, international political
responses to this fact have been
considerably less than spectacular at
this juncture.
Given that climate change is inevitable,
it is incumbent upon conservation
planners to integrate the current extent
of knowledge into their planning
ventures wherever possible.
Check your understanding of
Chapter 1
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1
2
3
4
5
6
7
The evidence for anthropogenic climate change
Global Climate Models
Climate change scenarios for Africa
Biodiversity response to past climates
Adaptations of biodiversity to climate change
Approaches to niche-based modelling
Ecosystem change under climate change
Chapter 8 Implications for strategic conservation planning
Chapter 9 Economic costs of conservation responses
I hope that you found chapter 1 informative, and that
you enjoy chapter 2.