Transcript Links between ozone and climate (John Pyle, Co-Chair, SAP)

Links between ozone and climate
J. A. Pyle
Centre for Atmospheric Science, Dept of Chemistry
University of Cambridge
Co-chair, SAP
7th ORM, Geneva, 19 May 2008
Historical reminder - a coupled chemistry/climate
system
GHGs, climate change and ozone
Ozone recovery
Ozone change and the climate system
Benefits of Montreal Protocol
Clx
T
Haigh and Pyle, 1982
Approx.
observed
T
Observed
T
consistent
with
changed
ozone,
CO2, etc
WMO/UNEP 1998, based on Hansen et al, 1997
GHGs climateO3
• GHGs will cool the stratosphere. This will influence
ozone loss by gas phase (make slower) and polar
heterogeneous (make faster) chemistry.
• GHGs - speed up the stratospheric circulation.
Impacts on stratospheric and tropospheric chemistry.
• Changed convection in a future climate - could
change delivery of (natural, short-lived) halocarbons to
the stratosphere.
• Other biosphere feedbacks could impact
stratosphere.
Ultraviolet
radiation change
Global
ozone
change
Ozone-depleting
chlorine and
bromine in the
stratosphere
ODS
production
Scientific Findings
(a)
ODS production
(b)
ODS in the atmosphere
Ozone levelsmeasured and
predicted
(c)
(d)
1980
Now
2100
UV levelsmeasured and
predicted
“There is even stronger evidence since the 2002
Assessment that the Montreal Protocol is working”
Return of ozone to pre-1980 levels
ODS are decreasing & the ozone layer is starting its recovery
Climate change and ODSs will affect the future of ozone layer
Decreases in ODS emissions already achieved by MP is the
dominant factor in return to pre-1980 values
Global ozone layer (60oS-60oN) is
expected to recover to pre-1980
values around 2050
But failure to continue compliance with the MP could
delay or even prevent the recovery of the ozone layer
O3/ODS  climate
Changed stratospheric ozone will change
tropospheric UV and IR.
ODS are GHGs - their change has a climate
forcing impact
• Impact on surface temperature
• Impact on tropospheric chemistry,
including through changed stratospheretroposphere transport
• Geo-engineering?
Radiative Forcing
• Positive direct forcing due to
all halocarbons:
0.34 ± 0.03 W/m2
• Positive direct forcing due to
ODSs only:
0.33 ± 0.03 W/m2
• Negative indirect forcing due
to ozone depletion:
-0.15 ± 0.10 W/m2
• Different types of gases
make different contributions
to positive and negative
forcing
IPCC/TEAP 2005
The Montreal Protocol net reduction
in ODS radiative forcing in 2010 will
be equivalent to about 7-12 years of
growth in radiative forcing of CO2
from human activities.
The Montreal Protocol will
have reduced net radiative
forcing from ODSs in 2010 by
about 0.23 Wm-2, which is
about 13% of that due to the
accumulated emissions of
CO2 from human activities.
G. Velders et al., PNAS, 2007
Antarctica
Hadley Center model
Observed temperature trend
• Cooling due to ozone depletion and warming due
to greenhouse effects of ODSs may not occur in
the same places and times
IPCC/TEAP 2005
The world avoided explored in the UKCA
chemistry/climate model
Chlorine
abundance under
different scenarios
Effective Cl could
have reached 9
ppbv at ~2030.
Surface temperature due to O3 in the
‘world avoided’ - a 9 ppbv Clx world
Simulated temperature change in
DJF (Gillett and Thompson, 2003)
Temperature change in 9 ppbv
simulation in SON.
Surface climate impacts
Without MP there would have been significant surface changes
Backup material
O3 (9ppb Clx - 3.5ppb)
These changes lead to a radiative forcing of
approximately -0.4Wm-2
Morgenstern et al, submitted, 2008
Radiative Forcing
• Positive direct forcing due to
all halocarbons:
0.34±0.03 W/m2
• Positive direct forcing due to
ODSs only:
0.33±0.03 W/m2
• Negative indirect forcing due
to ozone depletion:
-0.15±0.10 W/m2
• Different types of gases
make different contributions
to positive and negative
forcing
IPCC/TEAP 2005
Impact of Brx change
Zonal mean ozone change
ΔO3 (ppm)
ppm
Change in Brx increase ozone
destruction
Reduction of ozone concentration
below 30km
►-90 ppb high lat. / -50 tropics
►-8% UTLS / -2% 20-25 km
Olivier Dessens, Cambridge
Stratospheric Dynamics:
Circulation and Waves
Austin and Li, GRL, 2006
Climate models show a
strengthening of the
stratospheric circulation &
decrease in ‘age of air’ with
increasing GHG
concentrations
T (9ppb Clx - 3.5ppb)
Morgenstern et al, submitted, 2008
Change in modelled vortex strength between UM runs using 1980 and 2000
background ozone climatologies (20 years each).
1xCO2
Warmer, weaker vortex in “2000”.
2xCO2
Colder, stronger vortex in “2000”.
Ozone column
Percentage
change in
mean
annual
cycle of
ozone
column
Tropospheric climate
Geopotential height trend at 500
hPa (m) in DJFMAM from 1979 to
2000 (Thompson and Solomon,
2002)
Geopotential height difference vs
reference at 500 hPa in DJF.
Southern Annular Mode is strengthened by additional
chlorine.
Geopotential height in NH
Arctic oscillation pattern, derived
from 500 hPa geop. height in
winter (Thompson and Wallace,
1998)
Difference in geop. height
versus reference at 500 m
Arctic Oscillation is weakened by additional chlorine
 Brx (2100-2000) due to circulation changes