Links between ozone and climate J. A. Pyle Centre for Atmospheric Science, Dept of Chemistry...
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Transcript of Links between ozone and climate J. A. Pyle Centre for Atmospheric Science, Dept of Chemistry...
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
Approx. observed
T
Observed T
consistent with
changed ozone,
CO2, etc
WMO/UNEP 1998, based on Hansen et al, 1997
GHGs climateO3
• 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.
Scientific Findings
1980 Now 2100
OD
S
pro
du
ctio
n
Glo
bal
o
zon
e ch
ang
eU
ltra
vio
let
rad
iati
on
ch
ang
e
(a)
(b)
(c)
(d)
ODS production
ODS in the atmosphere
Ozone levels-measured and predicted
UV levels-measured and predicted
Ozo
ne-
dep
leti
ng
ch
lori
ne
and
b
rom
ine
in t
he
stra
tosp
her
e
“There is even stronger evidence since the 2002 Assessment that the Montreal Protocol is working”
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
But failure to continue compliance with the MP could delay or even prevent the recovery of the ozone layer
Global ozone layer (60oS-60oN) is expected to recover to pre-1980 values around 2050
Return of ozone to pre-1980 levels
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 stratosphere-troposphere 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
G. Velders et al., PNAS, 2007
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.
Antarctica
• Cooling due to ozone depletion and warming due to greenhouse effects of ODSs may not occur in the same places and times
Hadley Center model Observed temperature trend
IPCC/TEAP 2005
The world avoided explored in the UKCA chemistry/climate model
Chlorine Chlorine abundance under abundance under different scenariosdifferent scenarios
Effective Cl could Effective Cl could have reached 9 have reached 9 ppbv at ~2030.ppbv at ~2030.
Surface temperature due to O3 in the ‘world avoided’ - a 9 ppbv Clx world
Simulated temperature change in Simulated temperature change in DJF (Gillett and Thompson, 2003)DJF (Gillett and Thompson, 2003)
Temperature change in 9 ppbv Temperature change in 9 ppbv
simulation in SON. simulation in SON.
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
ppm
ΔO3 (ppm)
Zonal mean ozone change
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
Austin and Li, GRL, 2006
Climate models show a strengthening of the stratospheric circulation & decrease in ‘age of air’ with increasing GHG concentrations
Change in modelled vortex strength between UM runs using 1980 and 2000 background ozone climatologies (20 years each).
1xCO2 2xCO2
Warmer, weaker vortex in “2000”. Colder, stronger vortex in “2000”.
Ozone column
Percentage Percentage change in change in
mean mean annual annual
cycle of cycle of ozone ozone columncolumn
Tropospheric climate
Geopotential height trend at 500 Geopotential height trend at 500 hPa (m) in DJFMAM from 1979 to hPa (m) in DJFMAM from 1979 to 2000 (Thompson and Solomon, 2000 (Thompson and Solomon,
2002)2002)
Geopotential height difference vs Geopotential height difference vs
reference at 500 hPa in DJF.reference at 500 hPa in DJF.
Southern Annular Mode is strengthened by additional Southern Annular Mode is strengthened by additional chlorine.chlorine.
Geopotential height in NH
Arctic oscillation pattern, derived Arctic oscillation pattern, derived from 500 hPa geop. height in from 500 hPa geop. height in
winter (Thompson and Wallace, winter (Thompson and Wallace, 1998)1998)
Difference in geop. height Difference in geop. height versus reference at 500 mversus reference at 500 m
Arctic Oscillation is weakened by additional chlorineArctic Oscillation is weakened by additional chlorine