Download Document

We are now acting because the risks of inaction would be far
greater.
G.W. Bush’s Speech on Iraq March 16 2003
To me the question of the environment is more ominous than
that of peace and war. We shall have regional conflicts and use
of force, but world conflicts I do not believe will happen any
longer. But the environment, that is a creeping danger. I’m
more worried about global warming than I am of any major
military conflict.”
Hans Blix in an interview on MTV News,
Reported in New York Times, Sunday March 15 2003 “Hans Blix’s Greatest Fear”
Energy Balance
Since 1800: Atmospheric CO2 has increased by 30%
Increase in temperature // increase in greenhouse gases
Climate Forcing:
expressed as a change in radiative heating (W/m2) at surface for a
given change in trace gas composition or other change external to
the climate system
Cumulative climate forcing since 1800
Hansen PNAS 2001
Forced Cloud Changes:
anthropogenic aerosols may act as cloud
condensation nuclei
Jan 26 2001
Typical day: 700-800 planes
Sep 11 2001:
Air Force One +
9 military jets
Jet contrails
stimulated
growth of
cirrus
clouds 5 hrs
later
Decreasing area of
snow and ice
•Signal of warming
•Climate feedback:
• Increase surface
albedo
• Increase absorption of
solar irradiance
• Increase temperature
1500
2000
“Forced” vs “Natural” climate change
Temperature Trends
Glacial-interglacial
10 K /10,000 yr
= 1 K/1,000 yr
AD 1000-1600:
0.9K / 600 yr
= 0.15K /100 yr
Cannot be ruled out
AD 1980-2000:
Instrumental
0.5 K / 20 years
No evidence of abrupt
“natural” climate change
Uncertainty: natural climate variability on 102 - 103 years; abrupt climate change
For the next 100 years, natural variability unlikely to exceed 0.5K
Anthropogenically-forced climate change is real
Climate Forcing and Climate Feedbacks:
A given change in “external” climate forcing (e.g. 2xCO2) will trigger changes in the hydrologic system, atm circulation.
DT_realized = feedback factor x
DT_forcing
Change in surface air temperature
These “internal” changes will act to amplify or damp the initial forcing.
CO2: 300  600 ppmv
2
1.5
1
grd
albedo
cld
cover
cld
height
lapse
rate
water
vapor
(z)
-0.5
water
vapor
0
CO2
• feedback factor ~ 3.5
0.5
-1
-1.5
veg cover
sea ice
water vapor + clouds
-1.5
land ice
-0.5
-1
•Without CO2 decrease, cannot
explain cooling during the Last
Glacial Maximum
CO2: 300  200 ppmv
0
CO2
•Smaller feedback factor cannot
explain cooling during the Last
Glacial Maximum
-2
-2.5
Last Glacial Maximum
Energy Balance
Climate Change Signal
Climate Response
• Warming not globally uniform
• High-latitude amplification 
Albedo feedback
Global Climate Models used to project climate change from different CO2 scenarios:
Business as
usual CO2
emission
Stabilization of
CO2
Control
Holdridge Bio-Climate Classification
Climate change will alter the distribution of biomes
UN Framework Convention on Climate Change
• Ultimate objective: stabilizing greenhouse gas
concentrations in the atmosphere that would
prevent dangerous anthropogenic (humaninduced) interference with the climate system
• Such a level should be achieved within a time
frame to allow ecosystems to adapt naturally to
climate change, to ensure that food production is
not threatened, and to enable economic
development to proceed in a sustainable manner
1988
Intergovernmental Panel on Climate Change (IPCC) estab.
1990
IPCC 1st Assessment Report  real threat that by mid 21st century
human actions will have changed the basic conditions that permit life
Intergov Negotiating Ctte (INC) estab.
1992
UN Framework Convention on Climate Change (UNFCCC) estab;
“Earth Summit in Rio de Janeiro; Convention open for signatures
1994
UNFCCC came into force: recognition that climate change is a real
problem
1995
IPCC 2nd Assessment Report  evidence for human-induced climate
change; estimate “permissible emissions” to stabilize CO2 at 450
ppmv, 600 ppmv, ...; assessment of impacts of climate change
1997
COP3: Kyoto Protocol; developed countries to reduce their collective
emissions of 6 GHG’s (from 1990 levels) by at least 5% by 2008-2012
1998
Kyoto Protocol open for signatures; 84 obtained in one year
2001
IPCC 3rd Assessment Report  more evidence for human-induced
climate change
2002
World Summit on Sustainable Development; Johannesburg