Download lecture 34

NATS 101
Lecture 34
Anthropogenic
Climate Change
Anthropogenic Climate Change
The data indicate that global-mean land and
sea-surface temperatures have warmed
about ~0.6oC during the last century. Is this
the start of a man-made global warming?
Two main anthropogenic forcing mechanisms:
Greenhouse gas concentrations => rising.
Aerosol concentrations => also increasing.
We will focus attention on CO2 increases.
CO2 and the Greenhouse Effect
If the atmosphere were
dry, we could predict
with high confidence
that a doubling of CO2
(likely before 2100)
would increase the
global mean surface
temperature by ~2C.
Ahrens, Fig 2.10
The presence of oceans,
ice, water vapor and
clouds complicates the
analysis significantly.
Global Temperatures and CO2
There is a very strong
relationship between
CO2 levels and past
global temperatures.
CO2 levels are now higher
than during any period
of the past 450,000 years.
Will global temperatures
responding accordingly?
• Currently, 7 gigatons per year of CO2 are injected into
the air by burning fossil fuels (80%) and forests (20%).
• Half accumulates in atmosphere, where it resides for
50+ years.
• If the burning fossil fuels and forests totally ceased, it
would still take 50 years for CO2 levels to return to
50% above pre-industrial levels.
CO2 makes the biggest
contribution to the
climate forcing
US (5% of world population) now causes 20-25% of total pollution.
Projections of Global Warming
• Coupled Atmo-Ocean models are run for
hundreds of years to get future climates
• We assume continued increases in the levels of
greenhouse gasses in the atmosphere.
• The models have sophisticated physics…
But they have coarse grid separations!
Atmosphere: 250 km horizontal, 30 levels vertical
Ocean: 125-250 km horizontal, 200-400 m vertical
How Well Do Models Capture
Current Observed Climate?
• Performance Varies by
Weather Element
In general…
Excellent for Surface
Temperature
Skillful for Sea-Level
Pressure (SFC Winds)
Marginal Skill for
Precipitation
Fig. 8.4 IPCC Report
Global Temperature Outlook
Fig. 9.3 IPCC Report
Assume CO2 levels rise at
current rate of 1% per
year until 2070.
• Good agreement for past
climate and CO2 levels
leads to high confidence.
• Rather close agreement
among models.
Consensus of several
model runs indicates an
average warming of 2oC
Global Precipitation Outlook
Fig. 9.3 IPCC Report
• Marginal performance
for past climate and
CO2 levels means low
confidence in outlook.
• Large differences exist
among models.
Consensus of several
model runs indicates an
average increase of 2%
in global precipitation
Regional Consistency: Warming
Fig. 10.1.1 IPCC Report
A + or - symbol denotes 7 out of 9 models agree.
A2: no sulphate aerosols; B2: has sulphate aerosols
Regional Consistency: Rainfall
Fig. 10.1.2 IPCC Report
A + or - symbol denotes 7 out of 9 models agree.
A2: no sulphate aerosols; B2: has sulphate aerosols
GDFL Model
Lets look at some details from a 500-year
simulation by a specific climate model.
Examine Two Scenarios:
1% CO2 increase per year for 70 years
2X Total Increase in CO2
1% CO2 increase per year for 140 years
4X Total Increase in CO2
Good agreement for CO2
levels of the past 150 yrs
Mandatory before use as
global warming model
www.gfdl.noaa.gov
CO2 Increases
1% per Year
Average Global Surface
Temperatures…
Warm 2oC for 2X CO2
Warm 4o C for 4X CO2
Sea Level Rises…
Equilibrium Not Reached
until after 500 years
North Atlantic Ocean…
Circulation Weakens
www.gfdl.noaa.gov
CO2 Increases 1% per Year
• Surface Temperatures for GFDL Model
2X CO2 Temperature Animation Remote
2X CO2 Temperature Animation Local Disk
BIG File (8.2 MB)!!!
www.gfdl.noaa.gov
4X CO2 Sea Ice Animation
4X CO2 Sea Ice Local Link
CO2 Increases
1% per Year
July Temperature over
Southeastern U.S.
• Warms 5-9oC
July Heat Index over
Southeastern U.S.
• Rises 7-14oC due to
increase H2O vapor
Consistent Signal
Warmer Southern U.S.
www.gfdl.noaa.gov
CO2 Increases
1% per Year
Soil Moisture
• Much Drier over U.S.
60% Soil Moisture Decrease
Higher Evapo-Transpiration
Altered Balance between
Evaporation-Precipitation
• Agricultural Implications
How do we feed ourselves?
www.gfdl.noaa.gov
(Excludes Melting of Ice)
Sea Level Rises:
Consistent Model Signal
h=.000210  T  Depth
=.000210  1C  4000m
=0.8m
www.gfdl.noaa.gov
1 meter
2 meters
www.gfdl.noaa.gov
4 meters
8 meters
Increases in the frequency and/or the intensity of
extreme weather events is a likely consequence of
global warming.
GFDL Super Typhoon
Hurricane Intensities
Increase by 10%
Reason: Warmer Sea
Surface Temps
www.gfdl.noaa.gov
Key Points: CO2 Warming
• CO2 levels are rising and will likely double by 2070.
• The greenhouse relationship between higher CO2
levels and warmer temperatures is indisputable.
• Even with perfect knowledge of future CO2 levels,
there is significant uncertainty about how much
warming would occur and how fast it would occur.
• Model results suggest a 2oC global warming, with
strongest warming in polar regions, and an overall
increase in global precipitation.
• Shifts in precipitation are much more uncertain.
What Might We Do?
• Common sense precautionary measures suggest
that we begin to reduce emissions before enormous
changes to the climate and ecosystems could occur.
• Greenhouse warming is internationally recognized
as a serious problem.
• Kyoto Protocol is a good start, but the Congress
and Administrations have refused to ratify it or to
support attempts to curb greenhouse emissions.
• Consider supporting leaders and organizations who
provide vision and can make tough decisions.
What Can YOU Do?
• Nothing, after all you might be gone by 2070! Or…
• Insist on Energy Efficient Appliances-Merchandize
• Limit Heating and Air Conditioning
Programmable Thermostats
• Think Alternative Transportation
Bicycles, Walking, Public Transportation
• Practice Smart Use of Personal Automobiles
Carpool, Combine Errands, Lighter Loads, Slow
Down
Consider Fuel Efficient or Hybrid Vehicles
Assignment for Next Lecture
• NOVA: “What’s Up with the Weather?”