What are the best temperature data to use in estimating climate sensitivity? Lennart Bengtsson University of Reading, UK

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1 What are the best temperature data to use in estimating climate sensitivity? Lennart Bengtsson University of Reading, UK Ringberg Lennart Bengtsson 1

2 What we reasonably well know During the last 150 years CO 2 (equivalent) has increased from ca 280 ppmv to ca 480 ppmv or by ca 70% The increased forcing by the well mixed greenhouse gases amounts to ca 2.9 W/m 2 The corresponding 2m temperature (globally average) has increased by ca 0.8 C The correlason between forcing and temperature over the the last 100 years has been ca 80% We have no firm knowledge of ant. aerosol forcing but at the very first approxima>on it might be propor>onal to the emission. Ringberg Lennart Bengtsson 2

3 HadCrut3 temperature and NOAA/RCP forcing dt = C df = Watt/m 2 Ringberg Lennart Bengtsson 3

4 Surface temperature change Ringberg Lennart Bengtsson 4

5 Surface temperature change Ringberg Lennart Bengtsson 5

6 Surface temperature change Ringberg Lennart Bengtsson 6

7 What is the most suitable temperature to use in essmasng climate sensisvity? Surface temperature over land is exposed to a number of changes that are not related to large scale forcing. Examples are a number of other anthropogenic factors including agriculture, forestry, building and industry. There are general difficulses to adjust for UHI ( urban heat island) effects that are considerable also for smaller cises. External large scale forcing affects the whole troposphere at short >mescales due to rapid atmospheric processes. For this reason a greenhouse warming signal must also be detectable in the free atmosphere. Ringberg Lennart Bengtsson 7

8 At the Almeria region below the temperature has decreased by 0.3 C/decade due to increased albedo by 9% (Modis Terra) at the same Sme as other parts of southern Spain has been warming with a similar amount. Ringberg Lennart Bengtsson 8

9 The area with greenhouses covers some 260 km 2 Ringberg Lennart Bengtsson 9

10 ObjecSves of the study covering the period To compare different surface and upper air data sets. To compare temperature changes over land and ocean. To explore to what extent we can use re- analysis data from ECMWF Paper submiced to Tellus (Cederlöf, Bengtsson, Hodges) Ringberg Lennart Bengtsson 10

11 Area ECMWF re- analysis GISS HAD Global land 0.26 ± ± ± 0.06 Global ocean 0.06 ± ± ± 0.02 Global total 0.12 ± ± ± 0.02 NH land 0.34 ± ± ± 0.07 NH ocean 0.13 ± ± ± 0.03 NH total 0.21 ± ± ± 0.04 Surface temperature trends in C/decade for the period Ringberg Lennart Bengtsson 11

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16 AREA Trop ECMWF mb UAH TLT RSS TLT Glob land 0.10 ± ± ± 0.06 Glob ocean 0.11 ± ± ± 0.04 Glob total 0.11 ± ± ± 0.05 NH land 0.12 ± ± ± 0.07 NH ocean 0.13 ± ± ± 0.05 NH total 0.12 ± ± ± 0.06 Tropospheric temperature trends in C/decade Ringberg Lennart Bengtsson 16

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22 Area ECMWF re- analysis GISS HAD Global land 0.26 ± ± ± 0.06 Global ocean 0.06 ± ± ± 0.02 Global total 0.12 ± ± ± 0.02 NH land 0.34 ± ± ± 0.07 NH ocean 0.13 ± ± ± 0.03 NH total 0.21 ± ± ± 0.04 Surface temperature trends in C/decade for the period Ringberg Lennart Bengtsson 22

23 AREA Trop ECMWF mb UAH TLT RSS TLT Glob land 0.10 ± ± ± 0.06 Glob ocean 0.11 ± ± ± 0.04 Glob total 0.11 ± ± ± 0.05 NH land 0.12 ± ± ± 0.07 NH ocean 0.13 ± ± ± 0.05 NH total 0.12 ± ± ± 0.06 Tropospheric temperature trends in C/decade Ringberg Lennart Bengtsson 23

24 Summary of results Some of the available temperature datasets have limited geographical coverage but do not seem to affect global trends Warming trends over land are more than twice the warming over ocean. Re- analysis data can be used but care must be taken to changes in analysis methods over the period. ( Will be corrected in future versions). TLT from MSU cannot be compared to free atmospheric data due to land surface emissivity. Using tropospheric temperature data will imply a minor reducson (10-20%) in essmated climate sensisvity. Ringberg Lennart Bengtsson 24

25 Forecast , 00h+48h ICM Warsaw ( Schloss Ringberg( N 47 42, E ) END Thanks for your acenson Ringberg Lennart Bengtsson 25

26 Temperature change due to radiation perturbation(δf) including feedbacks. δt = λ o δf + f net δt f net = f a ( surf albedo) + f c (cloud) + f v water vapor) Ringberg Lennart Bengtsson 26

27 GCM Feedback components after Huybers (J. of Clim. 2010) Model/ feedback factor NCAR US MRI Japan GFDL US UKMO UK MPI Germany Ringberg Planck radiation λ o Albedo f a Cloud f c Lennart Bengtsson Water vapour Lapse rate f v Sum. av feedbacks f net

28 A numerical example. Cloud feedback dominates. δt = λ o δf + f net δt λ o is the Planck radiation effect δf radiation perturbation in W/m 2 f net is the sum of the feedback factors δf = 3.7 W/m 2 ( doubling of CO 2 ) δt for MPI 4.25 C but with cloud forcing from NCAR gives 1.92 C! Ringberg Lennart Bengtsson 28

29 Some remarks by Huybers (2010) The variance in cloud feedback, f c is almost twice at large as the net feedback f net. This suggests that the other feedbacks compensate for the variability in f c. The variance in f c and the covariance between f c and other feedbacks appear to be leading order terms in determining f net. Tuning climate sensitivity to lie within the observed spread across models is a sufficient explanation for the origin of compensation between f c and the other feedbacks Ringberg Lennart Bengtsson 29

30 Some Key problems Results from both empirical essmates and from models do vary considerably A key problem is that we do not know the forcing accurately enough. This is parscularly due to the effect of aerosols and interacson of clouds and aerosols There is no reason to assume that climate sensisvity is a constant of nature as it depends fully on the physical behavior of the climate system and changes in feedback structure. Ringberg Lennart Bengtsson 30

31 Global surface temperature 40 - year trends Time period Surface temperature trend , generally warming trend over extra-tropical land areas Marked Arctic warming , minor warming over oceans. Cooling over land by 0.20 C. Marked Arctic cooling , warming everywhere. Warming over land 3x as high as over oceans. Strong Arctic warming Ringberg Lennart Bengtsson 31

32 Ocean temperature trend ( C/year) Nov Oct 2013 (16 years) Ringberg Lennart Bengtsson 32

33 Cloud images Superstorm Sandy October day forecast Satellite Image IR Ringberg Lennart Bengtsson 33