1. WEATHER, CLIMATE
AND
HUMAN COMFORT

2. ACCLIMATIZATION Relative conditions more important than absolute
An organism’s adjustment to environmental changes
(e.g., temperature, humidity, day length, etc.)
Relative conditions more important than absolute
Ex. 65˚F day in January vs. July
Ex. Few excess heat deaths in Phoenix in summer
Ex. Low absenteeism from snow in Minneapolis
Debate on time required to adapt

3. HUMAN ENERGY BALANCE Q S M M = Metabolism (Heat - Work) IR
Q = Shortwave solar IR
IR = Infrared (in and out) M
M = Metabolism
(Heat - Work) S
S = Storage
SEN
SEN = Sensible (in and out) E
E = Evaporation (out only)
Processes that convert food to energy to sustain body’s functioning

4. HUMAN ENERGY BALANCE Q S Goal: Keep “S” close to zero MIR
SEN E S
Goal: Keep “S”
close to zero
M + Q ± IR ± SEN – E= ±S

5. COLD CONDITIONS – SEN insulating layer of air skin
Rapid sensible heat loss can result
– SEN
insulating layer of air
skin
Wind reduces insulating layer

6. WIND CHILL INDEX Combination of air temperature and wind speed
Assumes walking speed (3 kts)
Person not wearing clothing

8. HEALTH AND SEVERE COLD Wet clothing raises sensible heat loss
FROSTBITE: freezing of skin, extremities first
HYPOTHERMIA: rapid loss of body heat
Exhaustion
Loss of reasoning power
Stupor
Death
Often occurs above freezing!

9. HOT CONDITIONS Tw = 70˚F Tskin = 88˚F Strong Evaporation Rapid Cooling

10. HOT CONDITIONS Tw = 86˚F Tskin = 88˚F Reduced Evaporation
Slight Cooling
Tw = 86˚F
skin
Tskin = 88˚F

11. RAPID RISE IN BODY CORE TEMPERATURE!
HOT CONDITIONS
No evaporation—
body gains heat
from atmosphere
Tw = 90˚F
skin
Tskin = 88˚F
RAPID RISE IN BODY CORE TEMPERATURE!

12. HEALTH AND EXCESSIVE HEAT
Heat Cramps
Exercise in heat
Cramping of specific muscles
Fluid loss or electrolyte imbalance from excessive sweating and salt loss
Heat Exhaustion
Dizziness, weakness, fatigue
Slight elevation of body core temperature
Often related to fluid loss to replace perspiration
Heat Stroke
Body core temperature exceeds 105˚F
Sweating response shuts down, evap.cooling stops
Person becomes delirious or comatose
15% of those affected die

13. APPARENT TEMPERATURE (“Heat Index”)
Temperature a person “feels”
Summer equivalent of wind chill index
Depends on temperature and humidity
Some versions include wind speed

14. Apparent Temperature (Heat Index)
Page: 108
FIGURE 4.21 Air temperature (°F) and relative humidity are combined to determine an apparent temperature or heat index (HI). An air temperature of 96°F with a relative humidity of 55 percent produces an apparent temperature (HI) of 112°F.