Climate Past, Climate Present, Climate Future

Transcription

1 Climate Past, Climate Present, Climate Future Duglas Nychka, What is Weather? Climate? Climate knwns and climate mdels Uncertainty and climate Past Climate: Nrthern Hemisphere temperature Present Climate: Extreme rainfall Future Climate: Prjectins fr winter. Supprted by US NSF 7 th Wrld Cngress Prb. and Stat., Singapre July 2008

2 What is climate? Climate is what yu expect... weather is what yu get. Weather: Climate: Fr example, the 30 year average rainfall fr this area.

3 Why are we here? A changing climate.

4 Changes t ur atmsphere

5 The climate change tripd: In the last century 1. Glbal warming ver the last century 2. Increased greenhuse gases (e.g. carbn dixide) 3. Scientific evidence that greenhuse gases are the cause fr part f the warming.

6 Scientific basis: United Natins Intergvernmental Panel n Climate Change, Physical Science Basis, Summary fr plicymakers Cntributins f > 600 scientists and reviewed by 118 natinal representatives. 1. Glbal warming Warming f the climate system is unequivcal, as is nw evident frm bservatins f increases in glbal average air and cean temperatures, widespread melting f snw and ice, and rising glbal average sea level

7 2. Increases in greenhuse gases Glbal atmspheric cncentratins f carbn dixide, methane and nitrus xide have increased markedly as a result f human activities since 1750 and nw far exceed pre-industrial values determined frm ice cres spanning many thusands f years

8 3. Human activities as a cause Mst f the bserved increase in glbal average temperatures since the mid-20th century is very likely due t the bserved increase in anthrpgenic greenhuse gas cncentratins. Observatins with human greenhuse gases withut

9 Mre n Climate mdels The third leg f the climate change tri. A climate mdel is a cmputer cde based n physical principles that simulates the cmplex interactins between the many parts f the Earth system. It can be used t simulate current climate and make prjectins abut future climate.

10 Climate system mdel cmpnents:

11 Big Irn t run the mdels 1 day f supertime 5 years simulatin Snapsht f a high reslutin NCAR simulatin

12 Uncertainty Dnald Rumsfeld There are knwn knwns. These are things we knw that we knw. There are knwn unknwns. That is t say, there are things that we knw we dn t knw. But there are als unknwn unknwns. There are things we dn t knw we dn t knw.

13 We will use statistics t talk abut the knwn unknwns fr the Earth s climate Statistics uses a prbability distributin t describe uncertainty 50 years f daily rainfall >.25(mm) fr Bulder, CO. Density mm Mean is abut 1.6 (mm) Quite a bit f variability abut this value!

14 100 Weddings and the average cuple wedding J. Salavn Cabinet 15

15 Climate Past Nrthern Hemisphere Annual Temperatures B Li Caspar Ammann

16 Paleclimate temperature recnstructins Hw d we knw temperatures befre thermmeters? Surface temperatures are related t ther measurements: e.g. tree ring width, pllen, ice cres and brehles.

17 1000 years f Nrthern Hemisphere temperatures A summary f different recnstructins. Natinal Academy f Sciences Reprt: Surface Temperature Recnstructins fr the past 2000 years.

18 A statistical analysis three Mnte Carl samples shwing uncertainty 14 different annual prxy series and an energy balance mdel. Degree C Year Observed tempertures Mnte Carl samples 1 2 3

19 Nrthern Hemisphere temperatures with statistical uncertainty. Degree C Year Observed temperture 1000 samples Average, Standard deviatin

20 Climate Present Rainfall in Bulder Dan Cley Philippe Naveau

21 Extremes Smetimes the rare, but extreme, events are imprtant.

22 Extremes in current climate What is the size f a daily rainfall event that happens abut nce every 25 years? 100 years?

23 Observed precipitatin fr Bulder, CO Daily precipitatin amunts mm years This is nly 50 years f data!

24 Distributin fit t the Bulder exceedances... and the estimated 25 year event ( 9cm) with its statistical uncertainty. Density CM

25 Statistical analysis fr the Frnt Range Average sample Average frm 1000 Mnte Carl Samples

26 A map fr daily rainfall extremes fr the Clrad Frnt Range

27 Climate Future Winter cnditins fr Denver Stephan Sain Ruby Leung

28 Climate in the future Mdel Prjectin A climate simulatin fr the future based n a specific scenari f future human activities. e.g. Business as usual Reginal climate mdel (RCM) Cuples a weather mdel fr a specific regin t a glbal mdel t simulate finer reslutin. Reginal climate simulatin fr Western US. Ruby Leung (PNNL) 1% increase in CO 2

29 Prjected future changes under 1 % increases Difference: Prjectin minus Present sample Average Temp... Precip... Hw d we make sense f all this!

30 Values fr Denver, Clrad Temperature Change (C) Precipitatin Change (C) + Cntur cntains 50 % f the pssible changes... fr this climate mdel

31 My cities Difference: Mdel Prjectin minus Present Climate Precipitatin Change (C) Temperature Change (C)

32 Chices under uncertainty We have used statistical samples t characterize the uncertainty in sme climate prblems. The brad magnitudes f climate change and its cause at a glbal scale are largely knwn. Statistics can quantify the size f the knwn unknwns as we cnsider past climate, assessing present bservatins and future prjectins. The unknwn unknwns while beynd statistics are risks we may all share.

33 Thank Yu!