New Analysis of Old Ship Temperature Data Finds Ocean Warming Signature

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Here's the paper abstract: http://onlinelibrary.wiley.com/doi/10.1002/grl.50370/abstract

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New Analysis of Old Ship Temperature Data Finds Ocean Warming Signature

  1. 1. Can  we  detect  long-­‐term,  global  change  from  sparse,  135-­‐year-­‐old  ocean  data?  Will  Hobbs:  University  of  Tasmania,  IMAS  Josh  Willis  :Caltech/NASA  Jet  Propulsion  Laboratory  
  2. 2. Ar#st:  John  Steven  Dews  1.  Does  the  HMS  Challenger  data  provide  a  reasonable  esNmate  of  global  ocean  temperature?  2.  Is  the  esNmated  change  significantly  different  from  natural  variability,  parNcularly  prior  to  IGY?  3.  ImplicaNons  for  historical  esNmates  of  sea-­‐level  rise  
  3. 3. SpaNal  sampling  error  Trend  implies  bias  in  ΔT  st.  deviaNon  indicates  random  error    Total  uncertainty=  bias  +  √  (2  x  rand.  error2)    ±0.17oC  ±0.13oC  
  4. 4. Sounding  line  error  StaNons  prone  to  bias  are  clustered  in  the  Pacific  Equatorial  Counter  Current,  and  tend  to  show  cooling.    EliminaNon  of  these  staNons  increases  0-­‐730m  ΔT  by  0.06oC  (~  17  %)  
  5. 5. Summary  of  uncertainNes  StaNons  prone  to  bias  are  clustered  in  the  Pacific  Equatorial  Counter  Current,  and  tend  to  show  cooling.    EliminaNon  of  these  staNons  increases  0-­‐730m  ΔT  by  0.06oC  (~  17  %)  0-­‐730m  (0-­‐400  fm)   0-­‐1822m  (0-­‐1000  fm)    Precision    ±  0.014  oC   ±  0.014  oC  Sampling  error    ±  0.17  oC   ±  0.13  oC  Total    ±  0.17  oC   ±  0.13  oC  Sounding  line  bias    -­‐  0.06  oC  ?   -­‐  0.03  oC  ?  
  6. 6. Significance  of  temperature  change  –  natural  variability  PDFs  are  based  on  1000  random  temperature  differences  for  each  model,  between  Challenger  staNon  sub-­‐sampled  four  year  esNmates    99%  confidence  level  shown  by  red  line  Global  AtlanNc  Pacific  
  7. 7. Temperature  change  over  Nme  ’historical’  simulaNons  show  ΔT  consistent  with  Argo-­‐Challenger  esNmates  No  simulated  warming  in  ’historicalNat’  experiments  ’historical’  –  ‘historicalNat’  improves  agreement  between  models,  and  with  obs.  Argo-­‐Challenger  Levitus  et  al,2012  
  8. 8. 3)  Thermosteric  sea  level  rise  0.54  mmyr-­‐1  (Levitus  et  al,  2012)  0.50  mmyr-­‐1  0.74  ±  0.3  mmyr-­‐1  1.3  mmyr-­‐1  
  9. 9. 3)  Thermosteric  sea  level  rise  0.74  ±  0.3  mmyr-­‐1  Component   Early  20th  Century    Source  Sub-­‐2000m  thermosteric   O(10-­‐10  mmyr-­‐1)   CMIP5  historical    Glaciers  &  ice  caps   0.59-­‐0.68  mmyr-­‐1   Gregory  et  al,  2013  (1900-­‐1970)  Ice  sheets  -­‐  Greenland   -­‐0.33  to  0.31mmyr-­‐1    Gregory  et  al,  2013  (1900-­‐1970)  Terrestrial  storage   -­‐0.16  to  -­‐0.11  mmyr-­‐1  Gregory  et  al,  2013  (1900-­‐1970)  Total   0.49  (±  0.3)  mmyr-­‐1   Big  pinch  of  salt!  ‘Missing’  component   0.25  ±  0.4  mmyr-­‐1  
  10. 10. Conclusions  •  The  HMS  Challenger  observaNons  provide  a  reasonable  proxy  of  global-­‐mean  ocean  temperature,  albeit  with  large  uncertainty  •  Even  accounNng  for  this  uncertainty,  the  implied  early  20th  century  warming  is  highly  likely  to  due  to  an  anthropogenic  forcing  •  The  Challenger-­‐1955  ΔT  esNmate  implies  a  non-­‐thermosteric  contribuNon  of  0.50  ±  0.3  mmyr-­‐1  for  the  early  20th  century  
  11. 11. Profile  of  temperature  change  

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