It’s not just the heat, it’s the . Downscaled Wet-Bulb Temperature Projections and Implication for Future Summer Experiences from the American Climate Prospectus

D.J. RasmussenPROJECT DESCRIPTION RhodiumAn Group American Climate Risk Assessment

Next Generation, in collaboration with Bloomberg Philanthropies and the Economic Risks of Climate Change: An American Prospectus Paulson Institute, has asked Rhodium Group (RHG) to convene a team of climate scientists and economists to assess the risk to the US economy of global climate Trevor Houser Solomon Hsiang Robert Kopp change. ThisKate assessment, Larsen to conclude in late spring 2014,will combine a review Rhodium Group UC Berkeley Rutgers Universityof existing literatureRhodium Group on the current and potential impacts of climate change in Michael Delgado Amir Jina Michael Mastrandreathe United StatesShashank with Mohan original research quantifying the potential economic Rhodium Group Columbia University Stanford Universitycosts of the rangeRhodium of Group possible climate futures Americans now face. The report Robert Muir-Wood DJ Rasmussen James Rising will inform thePaul work Wilson of a high-level and bipartisan climate risk committee co- RMS Rhodium Group Columbia Universitychaired by MayorRMS Bloomberg, Secretary Paulson and Tom Steyer.

Supported by the Risky Business Project • Forthcoming from ColumbiaBACKGROUND University Press, AND SpringCONTEXT 2015

See abstracts: U13A-01, GC23F-03, PA24A-02, U31A-01, GC32A-07,From Superstorm GC41B-0549, Sandy to Midwest droughts to wildfires in the Rocky Mountains, our GC44A-05, PA54A-05 weather is becoming more extreme and more expensive. In 2012, climate and weather www.climateprospectus.org disasters cost Americans more than $110 billion. Not only was it the hottest year on record, but precipitation was 2.6 inches lower than last century’s average, leading to th massive10 East 40 crop Street, losses Suite 3601,across New the York, Heartland NY 10016 and wildfires covering more than 9 million Tel: +1.212.532.1158 | Fax: +1.212.532.1162 | Web: www.rhgroup.net ResourcesAGU forFall the FutureMeeting | American 2014 Climate • Prospectus:GC32A-07 Economic Risks in the United States acresMW in the3001 west. • 17 And December while Sandy 2014 was‹#› the most destructive storm of the year, it wasn’t the only one with a multi-billion dollar economic price tag.

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Both the US National Academies of Science and the Intergovernmental Panel on Climate 5 Columbus Circle Change (IPCC) have suggested that this kind of “iterative risk management” is also the right way to approach climate change. Using this framework, the scientific community is New York, NY 10019 preparing two major assessments of the risks to human and natural systems under a Tel: +1.212.532.1157 range of possible climate futures. The IPCC’s Fifth Assessment Report (AR5) will provide Fax: +1.212.532.1162 a global outlook, while the US government’s National Climate Assessment (NCA) will www.rhg.com

Humid heat extremes • The combination of high temperatures with high humidity is more uncomfortable, and potentially more dangerous, than high temperatures under drier conditions.

Increasing danger

• Humidity and high temperatures are leading cause of death from extreme weather events (e.g. 1995 heatwave)

2 Assessing humid heat stress with wet-bulb temperature • Wet-bulb temperature is the temperature measured by a fully ventilated thermometer with its bulb wrapped in a soaked cloth

• It reflects the ability of mammals to cool themselves by sweating Wet-bulb temperature records US: 33°C in Appleton,WI, on July 13, 1995 at 5pm (temperature of 38°C, of 32°C) 1995 Chicago heat wave experienced peak wet-bulb temperatures close to 32°C for consecutive days

An hour of vigorous, shaded activity at a wet- bulb temperature of 33°C raises core body temperature to the limit of 40°C.

3 Previous wet-bulb temperature studies using one GCM Sherwood & Huber (2010)

• With 11-12 ˚C of global mean warming much of southeastern U.S., areas of India and China uninhabitable during portions of the year Tw(max)(˚C) • Areas of uninhabitability could dwarf Community Atmosphere Model v3.1 that affected by rising sea level

Dunne et al. (2013) NOAA/GFDL - Earth System Model (ESM2M) • Global capacity to perform heavy labor reduces to less than 40% by 2200 in hottest months

• Eastern U.S. exposed to humid heat stress only present in hottest

regions of the present day RCP 8.5 WBGT≈0.7 x Tw + 0.3 x Td (˚C) (WBGT) Temperature Globe Wet-bulb

4 Compiling high-resolution projections of wet-bulb temperature

Challenges: • Multiple models used (probabilisitic approach; see Technical Appendix I of ACP) • County-level spatial scales

• No available humidity downscaling methods (obs. reliability?) Wet-bulb projection approach: Combine historical wet-bulb and dry-bulb temperature relationships from the North American Regional Reanalysis (NARR) with the probability distribution of local temperature change. Step 1: Estimate the conditional wet- and dry-bulb distribution Step 2: Use a linear model to shi! the conditional distribution

American Climate Prospectus: Economic Risks in the United States 5 Step 1: Estimate conditional distribution

Pittsburgh, PA Houston, TX NARR summer 1981-2010 NARR summer 1981-2010 ∆Tw /∆Td = 0.07 ˚C/˚C break point at ~28 ˚C Max. wet-bulb temperature (˚C) Max. wet-bulb temperature (˚C) ∆Tw /∆Td = 0.8 ˚C/˚C ∆Tw /∆Td = 0.8 ˚C/˚C

Dry-bulb temperature (˚C) Dry-bulb temperature (˚C) Depending on the Bayesian Information Criterion (BIC), fit a linear model or piece-wise linear model: Tw = wet-bulb temp. b0, b1= y-intercepts

Td = dry-bulb temp. T0 = break point

β0, β1, β2 = linear slopes

American Climate Prospectus: Economic Risks in the United States 6 Step 2. Use linear model to shift conditional distribution

• To account for the effects of climate change, we shift the conditional distribution upwards by a linear function of local forced temperature change:

= slope of standard linear regression

= local forced temperature change wet bulb temperature

dry bulb temperature

American Climate Prospectus: Economic Risks in the United States 7 Comparing empirical projections with a CMIP5 model (CNRM-CM5) 95th (2080-2099) 99th (2080-2099) Downscaled temperature & empirical relationships )

12.0 C ˚

10.5

9.0 Raw temperature & empirical relationships 7.5

6.0

4.5

3.0

Raw wet-bulb 1.5

0.0 anomaly ( - bulb temperature wet Max. RCP 8.5

Rasmussen et al. (in prep.) 8 Comparing empirical projections with a CMIP5 model (CNRM-CM5)

99th (2080-2099) ) 95th (2080-2099) C ˚ Downscaled temperature & empirical relationships vs. raw wet-bulb 4.0

3.2

2.4

1.6 0.8

0.0

Raw temperature & empirical relationships vs. raw wet-bulb -0.8 -1.6

-2.4

-3.2 -4.0 bulb temperature anomaly ( - bulb temperature wet in max. ifference D

Rasmussen et al. (in prep.) 9 American Climate Prospectus Humid Heat Stroke Index “It’s not just the heat, it’s the humidity.”

Peak Wet Bulb ACP HHSI Description (hottest part of day) Temperature

74°F-80°F I Uncomfortable. Typical of much of summer in the Southeast. (23.3°C-26.7°C) Dangerous. Typical of most humid parts of Texas and Louisiana 80°F-86°F II in hottest summer month, and most humid summer days in (26.7°C-30.0°C) Washington and Chicago. 86°F-92°F Extremely dangerous. Comparable to Midwest during peak III (30.0°C-33.3°C) days of 1995 heat wave.

Extraordinarily dangerous. Exceeds all U.S. historical records. >92°F IV Heat stroke likely for fit individuals after less than one hour of (>33.3°C) moderate activity in the shade.

American Climate Prospectus: Economic Risks in the United States 10 Projections from the American Climate Prospectus Dangerously Humid Summer Days Dangerously Humid Summer Days Expected number of Category III+ ACP Humid Historical Projected (RCP 8.5) 100 100 Heat Stroke Index days in a typical summer LA days MS FL AR AL MO SC KY IL DC TN IN DE HI OH NC VA NJ CT IA MD NY WV PA GA MN MA WI MI NE TX KS NH ME RI LA OK VT

10 days10 MS OR SD FL TX AR WA DC MO IL AZ SC ND TN KY AL IA OK IN KS VA NC DE NJ CT NE MD NY WI MN PA MA 1 day 1 GA OH

MI WV ME HI NH RI

NV Category II+ ACP HHSI days per summer

VT d

e CA

t SD c e p x

E 1 day/1 day/ decade OR decade MT

ND

ID 1 day/ AZ WA century1 day/ CA century 1981-2010 2080-2099 Expected Category II+ ACP Humid Heat Stroke Index days per summer, 2080-2099 American Climate Prospectus: Economic Risks in the United States 11 Key takeaways • Under RCP 8.5: • By late 21st century, dangerously humid Cat. II+ days are expected to characterize most of summertime in the eastern U.S., with > 50% of U.S. population expected to experience > 1 week of extremely dangerous Cat. III+ days year -1 • By late 22nd century, extremely dangerous Cat. III+ days are expected to characterize most of summertime in the eastern U.S., with > 30 extraordinarily dangerous Cat. IV days year -1

• Mitigation can greatly reduce risk. By late 21st century: • Under RCP 4.5, only 1/3 U.S. population expected to experience 1 Cat. III day year -1 • Under RCP 2.6, only ~4% of U.S. population expected to experience 1 Cat. III day year -1

12 Extra Slides Laboratory studies: reductions in labor productivity

240"

240"240

180" • Participants assembled

180"180 hardware under varying 34°C"34˚C 120" 34°C" 120"120 • Vitals signs (pulse, blood 36°C"36˚C 36°C" pressure, ect.) were 38°C"38˚C38°C" 60" 60"60 taken through out the 40°C"40˚C40°C" experiment safe%working%-me,%moderate%work%(minutes)%

safe%working%-me,%moderate%work%(minutes)% 00"

0" (minutes) work time, moderate working Safe 22"22 2626" 3030" 3434" 3838" 22" 26" Wet-bulbWet%bulb%temperature%(°C)% temperature30" (˚C) 34" 38" Wet%bulb%temperature%(°C)% • Safe working times decline as wet-bulb temperature increases at constant dry-bulb temperature

Liang et al. (2011) 14 Relative humidity is not expected to be stationary with global warming

Ensemble average of 27 CMIP5 models

2100 RCP 8.5 % Change in RH

• Reflected in slopes above the breakpoint, smaller ∆T_wet for ∆T_dry

Sherwood and Fu (2014) 15