Through  this  talk,  I  will  provide  an  overview  of  how  the  climate  change  research  community  aims  to  be  a  sen;nel,  or  a  party  that  keeps  watch,  over  the  economic  and  environmental  health  of  people  and  other  species.  They  do  this  through  a  variety  of  epistemological  tools,  such  as  observa;ons,  scien;fic  theories,  and  computer  models.  The  use  of  models  is  especially  important,  as  they  provide  the  ability  to  explore  uncertain;es  in  systema;c  ways.  Through  this  overview,  you  will  get  a  sense  of  how  my  research  interests,  which  are  around  socio-­‐economic  and  technological  choices,  are  related  to  Chris’  research  interests,  which  are  around  the  physical  climate.  Addi;onally,  you  will  see  how  the  rela;onships  between  these  communi;es  of  scholars  has  evolved  and  are  entering  a  new  phase.      

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Very  quickly,  before  I  get  into  my  presenta;on,  I  would  like  to  acknowledge  Naomi  Oreskes  for  providing  the  inspira;on  for  the  sub;tle  of  this  talk.  For  one  of  her  presenta;ons  at  the  Fall  2013  mee;ng  of  the  American  Geophysical  Union  this  past  December,  she  had  the  provoca;ve  ;tle,  “The  scien;st  as  sen;nel.”  Just  so  there’s  no  confusion,  my  views  of  “science  as  sen;nel”  are  different  from  hers,  but  there  is  a  nice  post  about  her  main  arguments  online  in  Limn  magazine.  Folks  should  check  it  out  if  they’re  curious.  

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For  my  presenta;on,  I’d  like  to  begin  by  poin;ng  out  that  scien;fic  work  around  climate  change  has  been  happening  for  a  long  ;me,  and  there  are  many  things  that  are  well  established.    The  fundamental  theore;cal  insight  of  earth’s  GH  effect  dates  to  work  in  1896  by  the  Swedish  physical  chemist  Svante  Arrhenius.  CO2  &  H2O  vapor:  gases  in  atmosphere  that  trap  heat.  This  suggested  changes  in  atm  concentra;ons  could  impact  avg  T  of  the  planet.    1930s,  engineer  Guy  Callendar  (with  some  Canadian  origins  by  the  way)  argued  that  fossil  fuel  burning  added  CO2  to  the  atm,  leading  to  an  observable  amount  of  warming.  He  assembled  T  records  from  1880-­‐1934  from  sta;ons  around  the  world  to  arrive  at  this  conclusion.    Late  1950s,  American  geochemist  Dave  Keeling  was  driven  to  produce  accurate  measurements  of  atmospheric  CO2.  In  just  2  years  (1958-­‐1960),  he  had  sufficient  data  to  conclude  the  atm  concentra;on  of  CO2  was  rising.  These  measurements  have  con;nued  ever  since.                

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Physical  climate  scien;sts  have  been  the  first  sen;nels  of  this  phenomenon.  Once  this  scien;fic  community  realized  that  enhancement  of  the  earth’s  natural  greenhouse  effect  was  real,  they  developed  detailed  computer  models  of  the  earth  system  to  inves;gate  how  surface  temperature,  precipita;on,  ice  melt,  sea  level,  and  a  variety  of  other  factors  could  be  affected  by  different  levels  of  greenhouse  gas  emissions.    Shown  here  is  the  observed  change  in  GAST  from  1950-­‐2010  as  a  black  line.  The  gray  shading  around  that  is  the  spread  of  42  climate  models  over  the  same  ;me  period.  As  you  can  see,  the  models  track  observed  T  quite  well,  which  gives  us  confidence  that  the  models  are  useful  representa;ons  of  reality.  (Normal  is  based  on  1986-­‐2005)    Now  that  we  have  that  confidence,  we  can  run  the  models  forward,  into  the  future,  to  see  what  may  be  in  store  under  different  levels  of  greenhouse  gas  emissions.  

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Here  we  see  the  comparison  of  two  cases  for  temperature  change  over  this  century:    -­‐A  red  case  analyzed  by  39  models  called  RCP8.5  -­‐A  blue  case  analyzed  by  32  models  called  RCP2.6    By  2100,  these  levels  of  climate  change,  which  are  based  on  equally  plausible  emissions  scenarios,  are  quite  different.    -­‐In  the  red  case,  T  change  averages  4degC  -­‐In  the  blue  case,  T  change  averages  1degC      As  you  can  see,  there  are  confidence  intervals  around  these  average  projec;ons,  and  Chris’  work  is  related  to  why  these  kinds  of  models,  when  projec;ng  future  changes  in  climate,  exhibit  this  kind  of  spread.    So what does the difference between 4deg and 1deg of climate change mean?

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A different community of researchers, those who focus on economic and environmental impacts, use the temperature projections produced by physical scientists to articulate the risks of different levels of climate change. The way to read this table is that each row describes impacts of climate change for a particular sector, such as water, ecosystems, or public health. The vertical white lines are like finish lines; as different lines are crossed, consequences of different severity become more likely. (READ EXAMPLES FOR FOLKS IN BACK) It’s pretty clear that all else being equal, more climate change is more dangerous. It would seem that our policy choices around climate change are quite simple: To avoid worse impacts from climate change, set lower global targets for greenhouse gas emissions. The lower the targets, the better. Things couldn’t be simpler, right?

Schweizer  Disserta;on  Defense,  May  4,  2010  

(2011  NAS-­‐NRC  report)    The  problem  is  that  this  brand  of  policy  advice  may  be  too  simple.  It  is  certainly  pervasive  –  this  is  the  cover  of  a  report  produced  3  years  ago  by  The  Na;onal  Academies  in  the  US.  The  clear  message  from  the  scien;fic  community  has  been  that  if  we  want  to  choose  a  future  climate  with  lower  risks,  we  should  choose  to  decrease  our  greenhouse  gas  emissions  as  much  as  possible  as  soon  as  possible.    However,  this  perspec;ve  speaks  to  only  one  element  of  the  complex  and  dynamic  system  of  human-­‐environment  interac;ons.  Just  as  the  average  global  temperature  could  change  by  1  deg  or  4  deg  by  the  end  of  the  century,  a  lot  of  other  things  will  change.    This  ques;on  is  not  simply  an  intellectual  one;  it  has  deeper  implica;ons  for  the  very  way  that  climate  change  research  is  done.  

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Returning  to  this  figure  from  the  latest  IPCC  report,  I  glossed  over  an  important  assump;on  frequently  employed  in  these  temperature  change  projec;ons.    I  said  previously  that  two  cases  were  being  compared,  one  called  RCP8.5  and  another  called  RCP2.6.  These  cases  refer  to  alterna;ve  hypothe;cal  outcomes  for  greenhouse  gas  concentra;ons.    [ANIMATE]  The  tradi;onal  paradigm  for  thinking  about  where  these  hypothe;cal  concentra;ons  come  from  is  to  see  them  as  the  result  of  a  par;cular  emissions  profile.  [ANIMATE]    In  turn,  the  emissions  profile  is  due  to  human  ac;vi;es,  which  are  subject  to  par;cular  socio-­‐economic  condi;ons.  [ANIMATE]    Under  this  paradigm,  socio-­‐economic  condi;ons  drive,  or  determine,  the  shape  of  the  temperature  projec;on.  

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An  alterna;ve  view  is  that  things  aren’t  that  simple.    We’re  shining  gears  in  this  figure,  because  what  you’re  looking  at  is  no  longer  some  temperature  projec;ons  but  some  global  CO2  emissions  projec;ons.  Here  the  amount  of  emissions  is  indexed  to  what  was  observed  in  1990.      The  light  blue  shading  summarizes  [LIT  REVIEW]  The  rainbow  lines  correspond  to  emissions  projec;ons  that  were  commissioned  by  the  IPCC  for  a  special  report.  What  I  would  like  to  call  your  aoen;on  to  are  the  ranges  on  the  far-­‐right  side  of  the  figure.  These  6  cases  of  A1FI,  A1B,  A1T,  A2,  B1,  B2  refer  to  6  hypothe;cal  sets  of  socio-­‐economic  condi;ons,  or  6  hypothe;cal  worlds.    [ANIMATE]  What’s  striking  is  that  there  is  substan;al  overlap  in  emissions  profiles  for  these  6  worlds.  The  socio-­‐economic  condi;ons  reflect  assump;ons  about  things  such  as  [ANIMATE].  A1  is  similar  to  B1  except  that  sustainable  development  is  not  a  priority,  so  economies  are  less  energy  efficient  and  don’t  necessarily  switch  away  from  fossil  fuels.      A  conclusion  that  has  been  drawn  from  this  overlap  is  that  human  choices  may  NOT    

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Revisi;ng  the  tradi;onal  paradigm  for  the  relevant  rela;onships  between  human  choices  and  climate  change,  there  is  nothing  incorrect,  per  se,  with  this  causal  view.    However,  the  climate  change  research  community  recognizes  that  there  are  shortcomings  with  the  tradi;onal  paradigm,  namely  that  …  [ANIMATE]    …the  conceptual  scaffolding  of  this  paradigm  is  incomplete.        

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Bearing  that  caveat  in  mind,  the  SRES  (that  is,  the  image  in  the  background  here  with  the  big  light-­‐blue  fan  and  overlapping  ranges  for  emissions)  pointed  out  that  a  different  conceptual  rela;onship  between  human  choices  and  climate  may  be  important  for  the  scien;fic  community  to  inves;gate.  Under  the  new  model,  some  aspects  of  the  tradi;onal  causal  model  are  retained,  for  instance  the  causal  rela;onship  between  greenhouse  gas  concentra;ons  and  changes  in  surface  temperature.    However,  mul;ple  socioeconomic  condi;ons  can  be  consistent  with  any  par;cular  mix  of  greenhouse  gases.  This  means  that  the  scien;fic  community  should  be  systema;cally  inves;ga;ng  two  “fans  of  uncertainty”:  Alterna;ve  levels  of  climate  change  AND  alterna;ve  socioeconomic  condi;ons.  

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Exploring  both  types  of  uncertainty  simultaneously  means  thinking  beyond  pegging  par;cular  socio-­‐economic  condi;ons  to  par;cular  levels  of  climate  change.  Instead,  to  have  a  beoer  calibrated  sense  of  the  risks  of  climate  change,  we  must  consider  alterna;ve  socio-­‐economic  condi;ons  in  the  face  of  any  par;cular  level  of  climate  change.  Because  mul;ple  socio-­‐economic  condi;ons  can  be  consistent  with  a  par;cular  amount  of  climate  change,  the  scien;fic  community  is  moving  beyond  thinking  about  individual  socio-­‐economic  scenarios  to  thinking  about  an  array  of  scenarios,  presented  here  as  a  matrix.        

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Currently  there  are  studies  underway  to  bound  the  uniqueness  of  human  choices  on  climate.    When  I  described  the  light  blue  fan  of  emissions  scenarios  with  ranges  of  overlap  between  some  socioeconomic  condi;ons,  not  all  of  them  overlapped  all  of  the  ;me.  Similarly,  it  is  expected  that  for  the  new  socio-­‐economic  scenarios,  some  levels  of  climate  change  will  be  “out  of  bounds”  for  par;cular  sets  of  socio-­‐economic  condi;ons.    However,  for  me  as  an  analyst  with  interests  in  socio-­‐economic  condi;ons,  the  parts  of  this  matrix  that  are  most  interes;ng  are  the  rows  where  mul;ple  socio-­‐economic  condi;ons  would  be  consistent  with  some  level  of  climate  change.    

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For  the  sake  of  argument,  let’s  pick  the  forcing  level  of  4.5  W/m2  by  the  year  2100.  Under  the  new  scenario  matrix  framework,  scien;fic  studies  that  consider  the  intersec;on  of  this  forcing  level  with  different  socio-­‐economic  condi;ons  in  slightly  different  contexts  can  be  compared.  -­‐Perhaps  one  global  study  of  policies  to  mi;gate,  or  decrease  greenhouse  gas  emissions,  considers  4  alterna;ve  socioeconomic  scenarios    

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For  the  sake  of  argument,  let’s  pick  the  forcing  level  of  4.5  W/m2  by  the  year  2100.  Under  the  new  scenario  matrix  framework,  scien;fic  studies  that  consider  the  intersec;on  of  this  forcing  level  with  different  socio-­‐economic  condi;ons  in  slightly  different  contexts  can  be  compared.  -­‐Perhaps  one  global  study  of  policies  to  mi;gate,  or  decrease  greenhouse  gas  emissions,  considers  4  alterna;ve  socioeconomic  scenarios    -­‐While  another  considers  2  alterna;ve  socioeconomic  scenarios  

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For  the  sake  of  argument,  let’s  pick  the  forcing  level  of  4.5  W/m2  by  the  year  2100.  Under  the  new  scenario  matrix  framework,  scien;fic  studies  that  consider  the  intersec;on  of  this  forcing  level  with  different  socio-­‐economic  condi;ons  in  slightly  different  contexts  can  be  compared.  -­‐Perhaps  one  global  study  of  policies  to  mi;gate,  or  decrease  greenhouse  gas  emissions,  considers  4  alterna;ve  socioeconomic  scenarios    -­‐While  another  considers  2  alterna;ve  socioeconomic  scenarios  -­‐And  maybe  a  mi;ga;on  policy  study  at  the  level  of  con;nental  regions  also  considers  2  other  socioeconomic  scenarios  

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For  the  sake  of  argument,  let’s  pick  the  forcing  level  of  4.5  W/m2  by  the  year  2100.  Under  the  new  scenario  matrix  framework,  scien;fic  studies  that  consider  the  intersec;on  of  this  forcing  level  with  different  socio-­‐economic  condi;ons  in  slightly  different  contexts  can  be  compared.  -­‐Perhaps  one  global  study  of  policies  to  mi;gate,  or  decrease  greenhouse  gas  emissions,  considers  4  alterna;ve  socioeconomic  scenarios    -­‐While  another  considers  2  alterna;ve  socioeconomic  scenarios  -­‐And  maybe  a  mi;ga;on  policy  study  at  the  level  of  con;nental  regions  also  considers  2  other  socioeconomic  scenarios  -­‐One  could  also  imagine  sector-­‐specific  studies,  such  as  for  transporta;on.    The  same  could  be  said  of  studies  that  focus  on  policies  to  adapt  to  climate  change,  or  that  es;mate  the  impacts  of  a  changing  climate  on  human  ac;vi;es  like  agriculture.  (green  shapes)    

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As  the  matrix  is  populated  with  the  findings  of  these  various  studies,  it  may  be  possible  to  look  across  the  constella;on  to  obtain  a  sense  of  the    -­‐Range  of  effort  to  mi;gate  greenhouse  gas  emissions  -­‐Range  of  adapta;on  possibili;es  -­‐Range  of  unavoidable,  or  residual  impacts  from  climate  change  as  a  func;on  of  the  COMBINED  clima;c  and  socioeconomic  condi;ons.    

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In  summary,  this  presenta;on  has  focused  on  how  the  scien;fic  community  has  explored  uncertain;es  around  climate  in  systema;c  ways.  I  did  not  focus  on  any  new  research  findings,  but  one  thing  that  is  always  important  to  tell  a  general  audience  is  [THERE  IS  NO  CONTROVERSY].    Through  this  presenta;on,  I  aimed  to  provide  you  a  sense  of  how  my  research  interests,  which  are  around  socio-­‐economic  and  technological  choices,  are  related  to  Chris’  research  interests,  which  are  around  the  physical  climate.  Addi;onally,  I  described  how  the  rela;onships  between  our  communi;es  of  scholars  have  evolved  and  are  entering  a  new  phase.        One  way  to  compare  and  contrast  the  priori;es  of  different  scien;sts  doing  climate  change  research  is  what  kind  of  sen;nels  they  are…  To  address  a  problem  as  big  as  climate  change,  we  need  both!        

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