Transcript Document

Chapter 16 – Global Warming
Elements of this chapter to keep in mind
 analyze and understand anthropogenic global warming and potential policies on global
warming from a scientific basis and in the context of past changes in climate – IPPC Ref.
 the relative sizes of the different carbon reservoirs and different carbon fluxes, in
particular the size of anthropogenic fluxes compared to natural fluxes
 the timescales of the various CO2 removal processes
 stress the chemistry of CO2 uptake in the oceans
 projections for future CO2 concentrations and predicted climatic implications of global
warming , including understanding the level of uncertainty that exists in climate models,
and the sources of these uncertainties
 anthropogenic gases other than CO2 contribute to the greenhouse effect
 understand how changes in greenhouse gases may affect sea level and ocean circulation,
in particular the thermohaline circulation
 impact of melting of ice caps – differences between Greenland and Antarctica ice sheets
 understand some of the impacts of global warming on ecosystems
Global Warming
• the potential impact of humans on the global climate system
• involves links between all the biogeochemical cycles with the
earth’s radiation balance
• Focus on the carbon cycle, as it has the primary impact:
The Greenhouse Effect
gtprate
beta switch
gross terr prod
ocn2atm
atm
weathering oc
o2arate
wocrate
respiration
atm2ocn
rrate
terr decay
goprate
surf ocean
gross ocn prod
a2orate
living marine bio
living terrestrial bio
tdrate
weathering cs
ocn decay
litterfall
lrate
revelle switch
wcsrate
urate
dead terrestrial bio
downwell
odrate
upwell
drate
noprate
organic sed
osrate
net ocn prod
deep ocean
inorg sed
organic c sediments
carbonate sediments
israte
Global Warming
The Greenhouse Effect
1. Radiation flux (independent
variable) as a function of
wavelength (dependent variable)
Area under curve gives total amount of
energy emitted by the two different bodies,
similarly for total absorption below
2. Absorption (in %) of different
atmospheric constituents as a
function of wavelength
3. Note absorption of long wave
radiation (infrared) of water
vapor and carbon dioxide
The Summary is divided into the following chapters:
• HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE
• DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE
• A PALEOCLIMATIC PERSPECTIVE
• UNDERSTANDING AND ATTRIBUTING CLIMATE CHANGE
• PROJECTIONS OF FUTURE CHANGES IN CLIMATE
The first four reflect the “detection and attribution” paradigm
HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE
HUMAN AND NATURAL DRIVERS OF CLIMATE CHANGE
RF = radiative forcing; LOSU = level of scientific understanding
DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE
DIRECT OBSERVATIONS OF RECENT CLIMATE CHANGE
UNDERSTANDING AND ATTRIBUTING CLIMATE CHANGE
Consumption rates, oil leads the pack
Climate Projections
1. Scenarios
1. Scenarios based on different
assumptions about economic,
social, technological, and political
changes in the future.
2. Assumptions are input into an
economic model, which give the
fossil fuel usage, and associated
carbon emission, as output.
Climate Projections
2. Changes in Atmosphere
1. Emissions from different
scenarios are put into carbon
cycles models, which keep track
of where the carbon goes
2. Other biogeochemical cycle
models that might be relevant to
climate (e.g. sulfur) are also used.
3. The focus is mostly on
atmospheric concentrations, which
can affect the radiative balance of
the earth
Summary from IPCC
Emissions from fossil fuels and
deforestation
Assumptions about population and
economic growth: a and b – modest
growth; c and d more rapid growth
a – most optimistic: increase 7 to
10Gton/yr by 2050 then decrease to 5
b – increase by about 0.7%/yr to reach
13Gton/yr by 2100
c – increase such that peak of 17Gton/yr
by 2050 and slow decline afterward
d – most of energy comes from fossil
fuels, reach peak 28Gton/yr (4 x
present!!) by 2080; a cumulative of
2000Gtons, almost ½ of all recoverable
fossil fuel reserves
Predicted concentrations
a – most optimistic: concentrations
of over 500 ppm by 2100
d – concentrations almost twice as
high as in case a., 1000 ppm by
2100, 2 doubling since pre-industrial
level, first doubling by 2050.
From 1D, radiative-convective CM:
doubling CO2 increases global
temperature by 2.5ºC (with H2O
feedback), doubling it twice can lead
to an increase of 5ºC (9ºF) over the
next century.
Note that so far warming is about
1ºC (0.7ºC), so these predictions
indicate that our climate might warm
faster than in the past.
Radiative forcing from other gases
Carbon dioxide, methane and nitrous
oxide - all linked to population,
anthropogenic activities, agriculture,
etc.
all contribute to the radiative
forcing (= change in outgoing IR
radiation flux due to change in
concentration of these gases)
Doubling CO2 - 4.4 W/m2, which
leads to 2.5ºC increase in
temperature according to SCMs, or
1.5-4.5ºC in GCMs
From the figure: CO2 - 1.5 W/m2,
CH4 - 0.5 W/m2, CO2 - 0.15 W/m2
over the past 1000 years
Our C-cycle lab, scenario 1
Our C-cycle lab, scenario 2
Our C-cycle lab, scenario 3
Our C-cycle lab, scenario 4
Climate Projections
3. Changes to the
Climate System
1. changes in atmospheric
composition are put into a climate
model, which calculates the
radiative balance of the earth, and
the resulting changes in the
distribution of energy and
temperature
2. particular attention is paid to
surface air temperatures and to
sea level rise – shown in the figure
is predicted trends in global Ts for
the four scenarios described before
IPCC 2001
IPCC
2007
Climate Projections
3. Changes to the Climate System
1. changes in atmospheric
composition are put
into a climate model, which
calculates the radiative balance of
the earth, and the resulting changes
in the distribution of energy and
temperature
IPCC 2001
2. particular attention is paid to
surface air temperatures and to
sea level rise – shown in the figure:
Predicted sea-level change for the
four scenarios described earlier;
range: 30 cm for scenario a. to 50
cm for case d.
Note: the concern is with the rate of increase, as this shows that it would be 2 to 3
times faster than the rate of increase in the past century
Climate Projections
4. Uncertainties
IPCC 2001
1. Uncertainties in every step are
addressed:
2. Economic, technological,
carbon cycle, and social
uncertainties are addressed by
including a large number of
scenarios
3. Climate model uncertainties are
addressed by including ranges of
results from different models
IPCCIPCC
20072007
PROJECTIONS OF FUTURE CHANGES IN CLIMATE
take-home messages:
Sea Level Rise
1. caused by an increase in the volume of water stored in the oceans.
What causes this increase in volume? Increase amount, decrease density
2. increase in the amount: Melting of ice that is on land
3. decrease in the density: thermal expansion
4. estimates of local
impacts must include
local vertical
movements due to
glacial rebound,
sedimentation changes,
and other local effects
global sea level follows
global temperature trend about 12 cm since 1880
Sea Level Rise
Sources of land-ice that might have contributed to past, and could contribute to
future, global sea level rise:
1.
Glaciers: believed to have contributed about half of past century’s global sea
level rise (the other half due to thermal expansion)
2.
Greenland ice sheet: contains enough water to raise sea level by 7 meters;
previous contribution to sea level rise is unknown, but most likely had a positive
contribution (lost mass during the past few decades).
3.
Antarctic ice sheet: contains enough water to raise sea level by
> 60 meters (East Antarctica) but it may melt less than Greenland’s. Also
snowfall may increase over Antarctica thickening the sheet over next century,
therefore global sea level MIGHT decrease instead. Ice flow on West Antarctica
is dynamic, and its potential response to climate change is unknown.
4.
West Antarctica: less water but behaves differently – here ice flows and forms
‘floating chunks’ (ice shelves) of ice grounded off the continents, if temperature
increases, they may become free-floating ice, generates friction, hence more
heat, hence more melting! This can add SIGNIFICANTLY to present prediction
of sea level rise due to Greenland’s ice sheet melt (which is most likely).
Ice Shelves: are grounded at
several points offshore;
affected by water
temperatures; if they are
removed, ice will flow faster
Ice Flow
West Antarctica
Sea level rise due to
1. Thermal expansion - half of rise
* 0.7 °C during 20th century responsible for about 7 cm rise
* changes in deep ocean: very slow, mostly due to Milankovitch cycles
which can be responsible for 5 msea-level fluctuations over longer period
(recorded)
2. Melting of mountain glaciers - this has been in the news as
being much faster and more widespread as previously thought
Changes in thermohaline circulation – possible impact
Possible changes to N. Atlantic downwelling, which could affect regional
temperatures. If the N. Atlantic freshens sufficiently, downwelling might
decrease, or cease, leading to cooler surface ocean and cooler regional climate.
1. Different plant species more
adapted to higher CO2 and higher
temperature levels.
e.g. C3 plants are expected to
increase productivity at elevated CO2
levels more than C4 plants; this could
affect agriculture.
3. Plant and animal migrations
expected to affect ecosystems;
different than earlier events because
of speed of change, and disruption of
migration paths by human settlement
Low water holding capacity
2. Forest composition expected to
vary, depending on temperature and
other environmental controls
High water holding capacity
Possible effects on ecosystems
Economics of Climate
Change
1.
Intergenerational equity:
benefiting from things for which
future generations will have to
pay; discounting costs and
benefits
2.
Other equity issues:
“Developing” vs “developed”
countries: who is more
responsible, those who emitted
in the past, or those in the future?
3.
Externalized costs:
Some of the costs associated
with “a product” are paid for by
society in general, not the
polluter. So, cost of cleaning up
are not included in the price.
Policies to mitigate global
warming
1.
Conservation – use less energy (not
likely to happen); plant trees;
2.
Alternative energy – using energy
from non fossil-fuel (non greenhouse
emitting) sources.
Nuclear, wind, tidal, geothermal,
biomass-based fuels, solar
3.
Methods to decrease CO2 emissions.
CO2 tax – extra tax on high-CO2
emission fuels; tax determined by
mpg regulations; carbon
sequestration