WEEK 8: Impacts of Climate Change
Climate Change and Heatwaves
• Denial 101 video
o Why heat waves are happening more often
o Can cause droughts, wildfires, crop failures
o Human-induced GHG emissions made it approx. x4 more likely that a summer
like Europe 2003 would occur
o Bell curve of getting cold, average, hot weather
▪ In normal climate, good odds for average weather but if global average
temperature goes up, whole bell curve will be shifted toward hot end
o Global warming = earth on steroids
▪ Equating extreme temperatures to hitting homeruns in baseball
o Combine effects of increase in average temperature and increase in “weirdness”,
expect heatwaves to be both hotter and frequency
o Night warming faster than days = fingerprint of global warming
▪ If nights hot, one more ingredient for extreme heat wave
o Will put more heat stress on people in some regions because heat index depends
on how humid the air is -> Hotter = more humid = more uncomfortable
o Myth that heat waves happened before so can’t say global warming causes them
now -> Non-sequitur fallacy
• Representation of 90th percentile of warm days
o Comparing historical amount of days we were above 90th percentile threshold was
around 10% early on, but moving forward to current times is now at 20% of days
exceeding the threshold
o Clear evidence of more warmer days associated with climate change
o Extending into future, see pretty big range in potential alternatives in the future
• Similar trend looking at cold days
o Early on in the record we have more cold days than the 10%, and have seen
coldest days decline approaching current times and for future projections
• Used to be that cold extreme vs warm extreme ratio was around 1:1
o But warm extremes occurring x4 (4:1 ratio) starting into the 200s
o Could find itself approaching even 10:1 in the future
o Will always be cold records in the future, but becomes exceedingly unlikely as
century moves on and as we look at really extreme scenarios
• Heat waves: period of marked unusual hot weather (maximum, minimum, daily average
temperature) over region persisting at least 3 consecutive days during warm
period of year based on local (station-based) climatological conditions, with
thermal conditions recorded above given thresholds
o Thresholds vary between regions
o ^World Meteorological Association definition requires it occur during the warm
part of the year i.e. not considered heat wave if occurring in mid-winter
o Matters for cardiovascular, respiratory, mental health perspective
o People most vulnerable are those with least resources to cool selves, considering
how climate change disproportionately significant on night temperatures
• Clear anthropogenic signal, studies demonstrating where signal emerged from the noise
o European summer heatwave had such a low probability of occurring,
wouldn’t have happened without anthropogenic influence
o 2010 summer averaged a lot above other anomalies, even 2003 summer
o France 2003 summer had 15,000 excess deaths due to event
• Important to recognize not all risks are distributed evenly spatially
• Global risk of deadly heat study (Mora et al., 2017)
o Series of more recent events that lead to large counts of excess mortality
o Looked at types of conditions present across the globe
o As you get to higher temperatures (upper 30s), if you combine with higher
relative humidity, more likely to have deadly heat event
o On annual basis, occur mostly in areas of lower latitude
o Using RCP 4.5, by end of century, projections of significant portion of year above
deadly threshold in key parts of world
▪ Northwest Africa, South America, southeastern Asia
▪ But also see some events in the United States, which hasn’t occurred in the
historical data
• Prairie Climate Center – Heat Waves and Health (special report on climate change)
o Definition of heat wave still using at least 3 days threshold, but using 30°C cut-off
o 2051-2080, admittedly with high carbon scenario (close to 8.5)
o Average number of heat waves per year across Canada
o Moving to the south (southeastern Ontario) see clusters that show lots of risk, also
moving into prairie regions
o If we look into northwestern Canada, see enhanced heat wave risk start to creep
up into territorial regions
o Shows that this risk not exclusive to southern Canada – although higher risk along
the interior – but can spread across the country
▪ Even coastal regions like Halifax; expected to increase to maybe 10/year
▪ Toronto and Ottawa; expected to not only increase in number of
heatwaves, but those that traditionally last 4/5 days may last 15-17 days
▪ Prairie region important agricultural zone, so heat waves will impact
ecosystems and food systems
• Lower water levels and flow -> Dry, dusty conditions -> Economic
losses -> Interrupted hydroelectricity
▪ Northwestern Canada also at risk of forest fires; expect longer, drier fire
seasons from more evaporation, also potentially more storms/lightning
o Still some atmospheric components we don’t completely understand how they
will impact heat waves
▪ Expecting increase in atmospheric blocking events -> Circulation patterns
that get stuck i.e. heat wave doesn’t break up
Climate Extremes
• Definition of heat waves i.e. Meteorological one -> Doesn’t mean we don’t get extreme
events outside of warmer seasons
o February 2010 arctic winter heat extreme; more common last few decades
o Huge swath of eastern Canadian arctic was +10°C above normal for February
o Extreme event but wouldn’t be called heat wave since it didn’t occur in summer
▪ Doesn’t mean impacts weren’t extreme for residents
▪ Mean temperature getting closer to 0°C which could lead to ice melt,
which can have profound impacts on remote communities
o Occurred during relatively cool conditions over Europe and the US
o Since major areas dominate the media outlet, people assume conditions were cold
• How a warmer arctic could intensify winter – Vox video
o Temperatures rising across world, with warming x2 fast in arctic
o Lost 3/4 of sea ice, covers 1/3 less of the ocean than it did 20 years ago
o Ice melts, turning reflective surface dark to absorb solar energy, warming up
▪ Without ice, more water evaporates, contributing to GHGs
o Earth’s air tends to move from warm middle of the planet to the poles
▪ Warm air takes more space so gravity pulls it toward Arctic, creating wind
▪ Earth spinning, creating polar jet stream (river of air) moving west to east
• Serves as boundary between cold air from Arctic and warm air
from tropics
• Arctic atmosphere changing as temperatures rise there faster than
further south
• Less gravitational pull on air towards North Pole, jet stream slows
o Less of flow, jet stream loses steam
• When curvy, weather sticks around longer, causing bigger storms,
droughts, cold spells
• Some think it’s supercharging extreme weather across world
▪ How polar jet stream affected US past winter (Jennifer Francis)
• Huge northward swing in jet stream over west coast, bringing lots
of warm air to Alaska -> Hottest December on record, with most
temperatures 20°F/30°F above average
• Took southward dive over Rockies and dipped into Florida
o Hadn’t seen measurable snow in over 30 years, but
happened; alligators got frozen into swamps
• Meteorologists called it a “bomb cycle”
• Then resulted in 20°F increase above average, before it brought
cold temperatures to Asia
o Extreme weather in North America occurring more often
▪ When Arctic very warm, very cold temperatures in eastern side of US
likely (“warm arctic, cold continents”)
• Areas in world where signal of Arctic impact on mid-latitude sometimes very robust,
while other studies find minimal impacts
• National security
o Hurricane Michael tore up hangars and buildings across Tyndall Air Force Base
in 2018; caused $5B in damage
o Series of reports from US context to assess potential risks/vulnerabilities across
bases, especially with sea level rise along coastal military installations
o Potential instabilities can impact intergovernmental interactions, and international
states with vulnerable groups
• Climate Wars – Syria video (Thomas Friedman)
o Link between climate change and immigration pattern of Syrians