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 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

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ODS production

ODS in the atmosphere

Ozone levels-measured and predicted

UV levels-measured and predicted

Ozo

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“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.

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

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

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 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

Brx (2100-2000) due to circulation changes