Transcript lecture25erk - The University of Arizona Department of

NATS 101
Lecture 25
Climate Change (cont’d)
The Natural Greenhouse Effect: clear sky
O3
8%
Carbon
Dioxide
26%
CH4
N20
6%
Water Vapor
Water
Vapor
60%
Carbon
Dioxide
Ozone
Methane,
Nitrous Oxide
Clouds also have a greenhouse effect
Kiehl and Trenberth 1997
CO2 makes the biggest
contribution to the
climate forcing
Global Warming Potential
(GWP)
Different gases has different warming potentials which
are defined relative to the warming effect of CO2
Gas
Carbon dioxide (CO2)
Methane (CH4)
Nitrous oxide (N2O)
Hydrofluorocarbons
Ahrens, Fig 2.10
Perfluorocarbons
Sulfur hexafluoride
GWP
1
21
310
560-12,100
6,000-9,200
23,900
Changing CO2 concentrations
• CO2 concentrations have varied naturally by ~3050% over the past few hundred thousand years (ice
ages)
• Fossil fuel burning since the industrial revolution
has created a recent sharp increase in CO2
concentrations
• CO2 concentrations are now higher than at any time
in past few hundred thousand years
Last
4 Ice Age
cycles:
• And
concentrations
are increasing faster with time
400,000 years
Man made
You are here
See http://epa.gov/climatechange/science/recentac.html
CO2
Temp.
Increasing CO2 concentrations
• How high will they go? How warm will it get???
• If CO2 concentrations stay within factor of 2 of pre-industrial,
then warming of 3+1oC is expected
• If concentrations go still higher => larger uncertainty
because the climate is moving into unprecedented territory
See
http://epa.gov/climatechange/science/futureac.html
You are going to be
somewhere in here
Last 4 Ice Age cycles:
400,000 years
Man made
You are here
Ice age CO2 range
Predictions of increased CO2 & Temperature
Emissions
High
Medium
Low
Constant 2000 CO2
Multi-model global averages of surface warming (relative to 1980-99) for
the scenarios A2, A1B and B1, as continuations of the 20th century
simulations. Shading is plus/minus one standard deviation range of
individual model annual averages.
Trenberth/IPCC
Missing
Carbon
Sink
Woods Hole web page
• CO2 is accumulating in the atmosphere more slowly
than expected (believe it or not)
• Based on our understanding of CO2 emissions and
ocean and atmosphere uptake, there is a missing
sink/uptake of about 25% NASA OCO mission
Ocean Carbon Uptake
QuickTime™ and a
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are needed to see this picture.
Ocean Uptake of CO2
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SciAm article
The Oceans & Global Change
• Much of this material is courtesy of
– Julia Cole, here in Geosciences at UA
and
– Kevin Trenberth at the National Center
for Atmospheric Research [NCAR]
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TIFF (LZW) decompressor
are needed to see this picture.
Ocean Transport of Heat
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3D “Conveyor Belt” Concept
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Potential Changes Related to the Ocean
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Change in Thermohaline Circulation
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Change in Ocean Chemistry
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Ocean Acidification
(SciAm article)
• Currently ~1/3 of CO2 released by burning fossil fuels
ends up in the ocean.
• Absorbed CO2 forms carbonic acid in seawater, lowering
the slightly alkaline pH level, changing the balance of
carbonate & bicarbonate ions.
• Shift toward acidity & ensuing changes in ocean chemistry,
make it more difficult for creatures to build hard parts out
of calcium carbonate.
• Decline in pH thus threatens a variety of organisms,
including corals, which provide one of the richest habitats
on earth.
• Within a century, Southern Ocean surface will be corrosive
to shells of tiny snails key in the marine food chain within
this highly productive zone.
Sea level is rising:
from ocean expansion and melting glaciers
Since 1993
Global sea level
has risen 43 mm
(1.7 inches)
• 60% from
expansion as ocean
temperatures rise,
• 40% from melting
glaciers
from Steve Nerem via Trenberth
Observed
Ocean Warming
• Most oceans are
warming
• Figures from Hansen et
al 2006
Evidence for reality of climate change
Glaciers melting
Muir Glacier, Alaska
1909
Toboggan
Glacier
Alaska
2000
1900
2003
Alpine glacier, Austria
Research indicates that less than 8°F of Arctic
warming caused Greenland to lose enough water
to raise sea level by up to 12 feet during the
Last Interglacial Period
Today
125,000 years ago
QuickTime™ and a
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Image from Bette Otto-Bliesner, National Center for Atmospheric Research
BUT, sea level rise during the Last
Interglacial Period appears to have been
more… it was likely up to 21 feet.
A reduced Greenland Ice Sheet could only
have contributed up to 12 feet…
Where did the rest of the water come from?
Today
Most likely
Antarctica…
East Antarctic
QuickTime™
a
Ice and
Sheet
TIFF (Uncompressed) decompressor
are needed to see this picture.
West Antarctic
Ice Sheet
http://svs.gsfc.nasa.gov
125,000 years
ago - the West
Antarctic Ice
Sheet may have
been gone
Late Quaternary
diatoms and
anomalously high
10Be found in
sediments under the
ice sheet
East Antarctic
Ice Sheet
1 meter
2 meters
www.gfdl.noaa.gov
4 meters
8 meters
Surface melt on Greenland
Increasing melt zones.
Melt descending into a
moulin: a vertical shaft
carrying water to the base
of the ice sheet.
NSIDC (above)
Braithwaite: Univ. Manchester
Greenland ice mass budget
A great deal of effort is going into
estimating how the Greenland ice
sheet is changing
Researchers
Mass Change Method
Time Span
(GT/year)
Krabill et al. 2000
-47
Aircraft Surveys 1994-1999
Velicogna et al. 2006 -200 to -260
GRACE
2002-2006
Luthcke et al. 2007* -145 to -175
GRACE 2003-2006
Zwally et al. 2007*
-80 to -100
ICESat
2003-2005
GRACE is a gravity recovery mission
ICESat is a lidar topographymission
NASA website on Greenland ice sheet
100 GT/yr ~ 0.3 mm/yr sea level rise
Snow cover and Arctic sea ice are decreasing
Arctic sea ice
area decreased by
2.7% per decade
(Summer:
-7.4%/decade)
2007: 22% (106 km2)
lower than 2005
Spring snow cover
shows 5% stepwise
drop during 1980s
Trenberth/IPCC
Arctic sea ice disappears in summer by 2050
Already 2007 lowest on record by 22%
Abrupt Transitions in Summer Sea Ice
2007
x
• Gradual forcing results in abrupt Sept ice
decrease
• Extent decreases from 80 to 20%
coverage in 10 years.
• Relevant factors:
• Ice thinning
• Arctic heat transport
• Albedo feedback
Trenberth from Holland et al., GRL, 2006
Land surface temperatures are rising faster than SSTs
SST
Land
Annual anomalies of global average SST and land surface air temperature
Land increased 0.4oC vs ocean suggesting 3% decrease in RH over land
Trenberth/IPCC
Human body: sweats
Homes: Evaporative coolers (swamp coolers)
Planet Earth: Evaporation (if moisture available)
e.g., When sun comes out after
showers,
the first thing that happens is that
the puddles dry up: before
temperature increases.
Trenberth
Water vapor increase at higher temperatures
Water holding capacity of atmosphere increases about 7% per oC (4%
per F) increase in temperature.
Observations show that water vapor in LOWER troposphere is indeed
increasing. Surface temperature increase: 0.6 C since 1970 over global
OCEANS and 4% more water vapor.
Total water vapor
Since late 1970’s, ocean surface has been warming at
~0.14 C/decade => ~1% WV increase/decade. Observed WV
trend since 1988 is ~1.2% per decade
From Trenberth/IPCC
Land precipitation is changing significantly over broad areas
Increases
Decreases
Smoothed annual anomalies for precipitation (%) over land from
1900 to 2005; other regions are dominated by variability.
Trenberth/IPCC
Proportion of heavy rainfalls: increasing in most land areas
Regions of disproportionate changes in heavy
(95th) and very heavy (99th) precipitation
Trenberth/IPCC
Declining Snow Pack in many mountain and continental areas
contributes to drought
• more precipitation falls as rain rather than snow,
especially in the fall and spring.
• snow melt occurs faster and sooner in the spring
• snow pack is therefore less
• soil moisture is less as summer arrives
• the risk of drought
increases substantially in
summer
•Along with wild fire
Trenberth
Drought is increasing most places
The most
important
Mainly decrease
in rain
over
spatial
(top)
land in tropics
and pattern
subtropics,
of the
but enhanced
by monthly
increased
Palmer
Drought
atmospheric
demand
with
Severity Index
warming
(PDSI) for 1900 to
2002.
The time series
(below) accounts for
most of the trend in
PDSI.
Trenberth/IPCC
Rising greenhouse gases are causing climate
change, and arid areas are becoming drier
while wet areas are becoming wetter.
Water management:dealing with how to save in times of excess
for times of drought –
will be a major challenge in the future.
Trenberth
Heat waves and wild fires
Impacts on human
health and mortality,
economic impacts,
ecosystem and
wildlife impacts
Trenberth
Extremes of
temperature
are changing!
Observed trends
(days) per
decade for 1951
to 2003:
5th or 95th
percentiles
From Alexander et
al. (2006)
Trenberth/IPCC
Global Atmo Energy Imbalance
Increasing GHG concentrations decrease Energy out
So Energy IN > Energy OUT and the Earth warms
IR Out
is reduced
Ahrens, Fig. 2.14
Solar in
Atmosphere
Heat waves are increasing: an example
Extreme Heat Wave
Summer 2003
Europe
30,000 deaths
Trend plus variability?
Trenberth/IPCC
Trenberth
CO2 emissions in different regions in 2000 in terms of emissions per
capita (height of each block); population (width of each block); and
total emissions (product of population and emissions per capita =
area of block).
Source: M. Grubb, http://www.eia.doe.gov/iea/
Trenberth
Trenberth