Observed Global Warming and Climate Change

Transcription

1 Observed Global Warming and Climate Change

2 First Dice Activity

3

4 natural state human activity

5 measured global warming of Earth s surface primarily caused by anthropogenic increase in greenhouse gases

6 Ozone, CO 2, not much H 2 O weather From Hartmann

7 Radiative Balance of the Stratosphere solar flux top of atmosphere stratosphere solar flux aborbed by ozone tropospheric flux absorbed by CO 2 stratospheric flux emitted by CO 2 troposphere upwelling flux from troposphere and surface

8 Radiative Balance of the Stratosphere ε O3 F solar + ε CO2 F trop = 2 ε CO2 T strat 4 ε O3 is fraction absorbed by ozone ε CO2 is fraction absorbed/emitted by CO 2 F solar is downwelling solar flux F trop is upwelling thermal flux from troposphere T strat is stratospheric temperature

9 Divide into Four Teams

10 Radiative Balance of the Stratosphere ε O3 F solar + ε CO2 F trop = 2 ε CO2 T strat 4 How will stratospheric temperature T strat change if solar flux F solar increases? ozone decreases? CO 2 increases? How will surface temperature T sfc change if solar flux increases? ozone decreases? CO 2 increases?

11 What Caused Recent Global Warming? Natural Increase in solar flux Not natural Increase in CO 2 by burning fossil fuels Decrease in ozone from CFCs

12 Theoretical Prediction Solar flux increases Surface and troposphere warm Stratosphere warms CO 2 increases Surface and troposphere warm Stratosphere cools Ozone decreases Surface and troposphere warm Stratosphere cools

13

14 Observational Confirmation Temperature changes are in the directions that theory predicts But what if the observed temperature changes are merely the results of weather fluctuations?

15 Hypothesis Testing Was the effect produced by a real cause, or did it happen by coincidence or chance? Null hypothesis: effect by chance Alternative hypothesis: a real cause What is the probability that the observed effect could have occurred by chance? Low probability by chance: reject null hypothesis High probability by chance: reject alternative hypothesis

16 Recent Temperature Increase

17 Recent Temperature Increase Is the recent temperature increase produced by an external cause or by natural temperature fluctuations? Null hypothesis:? Alternative hypothesis:?

18 Recent Temperature Increase Is the recent temperature increase produced by an external cause or by natural temperature fluctuations? Null hypothesis: natural random temperature fluctuations Alternative hypothesis: a systematic change/trend What is the probability that the temperature increase could have occurred by chance? Low probability by chance: reject null hypothesis High probability by chance: reject alternative hypothesis

19 Recent Temperature Increase

20 Create Statistical Model Focus on last 60 years 6 Average temperature over each decade

21 Calculate the increase from the first three decades to the last three decades C 0.35 C 0.20 C 0.05 C 0.00 C What is the probability that an increase as large as the observed increase could have occurred in a random sequence of decadal temperature values?

22 Random sequence C 0.35 C 0.20 C 0.05 C 0.00 C

23 Random sequence C 0.35 C 0.20 C 0.05 C 0.00 C

24 Monte Carlo Method Create 100 random sequences What fraction of sequences have a temperature increase smaller than the observed temperature increase? If 95% or more sequences have a smaller temperature increase, reject null hypothesis (observed increase is only random) Instead, observed increase is systematic

25 Second Dice Activity

26 Formal Test: Are Two Sums Different? z-score = (actual diff expected diff) / (N standard dev) actual diff = 1.05 C expected diff = 0.0 C N = 3 standard dev = sqrt(var 1 + var 2 ) = C var 1 = variance of {0.00, 0.00, 0.05} var 2 = variance of {0.20, 0.35, 0.55} z-score = ( ) / (3 0.18) = +1.96

27

28

29 Formal Test: Are Two Sums Different? z-score = (actual diff expected diff) / (N standard dev) z-score = ( ) / (3 0.18) = 1.96 one-sided p-value = 0.975

30 Student s t-distribution z-score = (actual diff expected diff) / (N standard dev) z-score = ( ) / (3 0.18) = 1.96 degrees of freedom = 2N 2 = 4

31

32 Student s t-distribution z-score = (actual diff expected diff) / (N standard dev) z-score = ( ) / (3 0.18) = 1.96 degrees of freedom = 2N 2 = 4 one-sided p-value = between 0.90 and 0.95