Global&hydrological&cycle&response&...

Global  hydrological  cycle  response  to  rapid  and  slow  global  warming    

Larissa  Back,  Kuniaki  Inoue,  Karen  Russ,  Zhengyu  Liu  

*Simulations implemented by Feng He and Jiaxu Zhang

•  Anthropogenic  global  warming  causes  “robust”  changes  in  the  global  hydrological  cycle  

•  “Robust”  changes  (in  this  context)  means  changes  are  directly  related  to  global  mean  temperature  change*  

•  QuesFon:  Are  hydrological  cycle  changes  in  the  paleoclimate  (last  22ky)  similarly  “robust?”  – Answer:  Only  sort  of.    We’ll  examine  why  this  is.      

Outline:  

*e.g.  Held  &  Soden  2006  

“Robust”  changes  in  the  global  hydrological  cycle  due  to  anthropogenic  

global  warming  

Atmospheric radiative cooling constraints (surface energy

balance)

Held & Soden, 2006

“Robust”  rainfall  changes:  wet  get  weTer  and  the  dry  get  drier  

S  

Fig. 6b From Held & Soden (2006) Latitude

SRES A1B scenario

Zhengyu Liu (UW-Madison), B. Otto-Blienser (NCAR)

Realistic Forcing

Insolation GHGs Meltwater Icesheet

Model: NCAR-CCSM3 – fully coupled ocean-atmosphere GCM

Liu et al., 2009, Science

Greenland Temperature Obs (grey), Model (red)

Unexpected  TRACE  paleoclimate  results:    q  (global  water  vapor)  versus  surface  T  

Surface Temperature (C)

“surface-CC scaling:” 6.7%

shows  4.2  %  q  increase  per  unit  T  change.      

At apparent odds with: Consistent with

Boos 2012 results

Unexpected  TRACE  paleoclimate  results:    q  (global  water  vapor)  versus  surface  T  

Surface Temperature (C)

“surface-CC scaling:” 6.7%

shows  4.2  %  q  increase  per  unit  T  change.      

At apparent odds with:

Slope increases during anthropogenic warming era to 7.2 %

Possible  explanaFons  for  4.2%  water  vapor  increase  per  unit  K  warming    

•  Rela%ve  humidity  is  not  constant  over  climate-­‐change  %me  scales?  

•  Clausius-­‐Clapeyron  rela%onship  non-­‐lineari%es?    

•  Tropical  upper  troposphere  warms  more  than  surface  at  warmer  temperatures?  

•  Rapid  CO2-­‐induced  warming  affects  global  water  vapor  differently  than  slow  CO2-­‐induced  warming?  

56%

57%

8 C

12 C Total water vapor in atmosphere

Total water vapor atmosphere would have if saturated

Blue shows:

Column relative humidity changes small

Rela%ve  humidity  is  not  constant  over  climate-­‐change  %me  scales?  

Try  changing  CO2  rapidly  by  running  branch  simulaFons  where  CO2  doubles  instantaneously  

Time (ka BP)

CO2 doubling

CO2 doubling

CO2 doubling

Anthro- pogenic

Try  changing  CO2  rapidly  by  running  branch  simulaFons  where  CO2  doubles  instantaneously  

CO2 doubling

CO2 doubling

CO2 doubling

Anthro- pogenic

‘s = “Rapid” warming

Time (ka BP)

Rapid  CO2-­‐induced  warming  affects  global  water  vapor  differently  than  slower  warming  

Surface Temperature (C)

“surface-CC scaling:” 6.7%

Rapid warming d(lnq)/dT greater than slow warming d(lnq)/dT

 Slow  CO2  increases    symmetric  warming  

Rapid  CO2  increases    N.H.  warms  more  

dominates  response  

 response.    

“Slow”  

“Rapid”  

Latitude

Figure shows amount of surface warming by latitude normalized for a global surface T increase of 1K

S. Ocean thermal inertia

 Slow  CO2  increases    symmetric  warming  

Rapid  CO2  increases    N.H.  warms  more  

dominates  response  

 response.    

“Slow”  

“Rapid”  

Latitude

Figure shows amount of surface warming by latitude normalized for a global surface T increase of 1K

 Slow  CO2  increases    symmetric  warming  

Rapid  CO2  increases    N.H.  warms  more  

dominates  response  

 response.    

“Slow”  

“Rapid”  

Latitude

More  tropical  warming  per  global  T  increase  

Figure shows amount of warming by latitude normalized for a global T increase of 1K Figure shows amount of surface warming by latitude normalized for a global surface T increase of 1K

Consider  a  hypotheFcal  3-­‐box  model  of  warming  paTerns  

•  Assume  most  water  vapor  is  in  tropics  due  to  warmest  temperatures  there    – Water  vapor  increases  exponenFally  with  T  

•  Assume  warming  paTern  in  3  equal-­‐area  boxes:  

•  “Slow”  has  less  global  d(lnq)/dT  than  “rapid”  case  

S. H. N. H. Tropics

Rapid

Slow

0

1 0 1

1 1

Real  3-­‐box  model  numbers,  where  each  box  has  equal  area,  support  

interpretaFon  •  For  1  degree  global  temperature  change:  

S. H. N. H. Tropics

Rapid

Slow

0.75

1.4 0.42 1.2

0.71 1.5

Why  does  global  water  vapor  increase  more  (%  per  K  global  T  change)  in  response  to  rapid  (anthropogenic-­‐like)  CO2  change?  

•  Most  water  vapor  is  in  the  tropics    -­‐-­‐>  amount  of  tropical  warming  strongly  influences  global  water  vapor  change  

•  Tropics  warm  more  (per  unit  global  T  change)  if  warming  is  concentrated  in  one  hemisphere  

•  Therefore,  one-­‐hemisphere  warming  -­‐-­‐>  larger  global  water  vapor  increase  (%)  per  K  global  warming  

€

q = q0eαδT

Global water vapor

Function of initial water vapor & delta T

Local mixing ratio increases at

Clausius-Clapeyron

AlternaFve  predicFon  of  global  water  vapor  increases:  

€

δT = δT +δT ' = Mean surface T change + perturbation T change

Correction due to inhomogeneous temperature increases

Slow

Rapid

4.3 %

6.2 % 6.6 %

6.7%

-0.3 %

-2.6 %

AlternaFve  theoreFcal  predicFon  of  water  vapor  increases  matches  

simulated  increases  

TRACE  Paleoclimate  results:  Global  precipitaFon  vs.  surface  T  

“Slow”  and  “Rapid”  cases  behave  similarly  

P  increases  at  1.9%  per  unit  surface  T  warming  

Global Temperature (Celsius)

TRACE  paleoclimate  warming:  Wet  [mostly]  get  weTer  &  dry  [mostly]  get  drier  

Latitude

For a 1 degree global surface T change:

“thermodynamic” scaling

Mean Δ(P-E) and +/- a standard deviation

Rapid  CO2  doubling:  Wet  [mostly]  get  weTer  &  dry  [mostly]  get  drier  

Latitude

For a 1 degree global surface T change:

“thermodynamic” scaling

Mean Δ(P-E) and +/- range (for CO2 doubling cases, anthropogenic)

“Rapid”  &  “Slow”  T  changes  lead  to  somewhat  different  precipitaFon  changes  

Latitude

For a 1 degree global surface T change:

Rapid Slow Thermodynamic

scaling (dashed lines) is similar for rapid and slow changes.

Modeled changes significantly different

Hydrological  cycle  changes  in  TRACE  paleoclimate  (last  22ky)  compared  to  rapid  (anthropogenic-­‐like)  CO2-­‐induced  changes:  •  Global  water  vapor  increases  less  (per  unit  warming)  in  TRACE  paleoclimate  – Longer  Fmescale  of  S.  Ocean  adjustment    different  spaFal  paTern  of  warming  for  rapid  vs.  slow  warming  

– most  q  in  tropics  (Clausius-­‐Clapeyron  non-­‐linearity)    global  dlnq/dT  dependent  on  tropical  warming  amount  

•  Global  mean  precipitaFon  changes  comparable  

•  Zonal  precipitaFon  paTern  changes  somewhat  different  due  to  circulaFon  paTern  changes    

“Local”  d(ln  q)/dT  by  la%tude  and  height    

•  Is  a  range  of  dq/dT  (%  change  water  vapor  per  unit  warming)  

“Rapid”  warming  

“Slow”  warming  

Latitude

“Local”  temperature  change  paHerns:  

•  Put  Karen’s  figure  in  showing  T  change  here  

•  Or  show  my  figure  from  my  idealized  model…