The Effect of Climate Change on Human Health

The Effect of Climate Change on
Human Health
Spring 2012, Lecture 13
Overview of Effects
• Climate change is expected to have a major influence
on certain types of disease
• Changes in both temperature and humidity will play
an important role
• Some of the effects are already being seen
• Some increased health risk will be due to extreme
weather events, like the 2010 heat wave in Russia, but
many problems will involve continual climate
Increased Risk and Benefit
• Some climate changes may produce health
benefits, but most will increase risk
• The following slides outline a few examples
Increased Heat
• Risk - More deaths and increased disease risk
due to very hot days
• Benefit – Fewer winter deaths and disease
Heat-wave Effects
• According to the IPCC Fourth Assessment
(2007), by 2100:
o Chicago is projected to experience 25% more
frequent heat waves
o Los Angeles is expected to experience a four to
eight-fold increase in heat-wave days
• Those with heart problems, asthma, the
elderly, the very young and the homeless can
be especially vulnerable to extreme heat
Heat Stress
Schematic representation of how an increase in average annual temperature
would affect annual total of temperature-related deaths, by shifting distribution
of daily temperatures to the right
Additional heat-related deaths in summer would outweigh the extra winter deaths
averted (as may happen in some northern European countries)
Average daily temperature range in temperate countries would be about 5–30ºC.
Food Poisoning
• Risk increases due to higher temperatures
• Salmonellosis is especially likely to be a
Aero-allergen Production
• Risk – Increased allergic disorders, including
hay fever and asthma due to longer pollen
• Benefit – Reduced exposure to aero-allergrens
in some places due to lower productions or
shorter seasons of pollen circulation
o Higher temperatures and changed humidity may
make the growing seasons shorten for some plants
Effects of Extreme Temperatures
• A European study of hospital admission data for a
dozen major cities found that for every 1ºC rise in
temperature, hospital admissions for respiratory and
asthma-related illness increase up to 4.5% among the
• The Russian heat wave of 2010 doubled the death rate
in Moscow to 700 people per day during the heat
• During the summer 1995 heat wave in Chicago, it is
estimated there were 700 excess deaths due to heat
Water-borne Infection
• Risk - Cholera risk will increase in coastal or
estuarine regions, due to a warming of water
• Benefit – risk will diminish in areas where
heavy rainfalls decrease
Vector-borne Infections
• Risk – Both mosquito and tick borne infections
are likely to increase
• Benefit – In areas of diminished rainfall,
mosquitoes, ticks, and snails may become less
prevalent, and regions of very high
temperatures may also decrease these vectors
Vector-borne Disease and Climate
• Vector-borne diseases have been shown to be
associated with changing climate conditions,
especially El Nino-Southern Oscillation
(ENSO ) events
o Malaria – South Africa, Columbia, Venezuela
o Dengue fever – Asia-Pacific
o Ross river virus – Australia
o West Nile – Numerous places, including the U.S.
Vector-borne Disease
• In epidemiology, a vector is an insect or any living
carrier that transmits an infectious agent
• A vector serves two functions:
o It is required for part of the parasite's developmental cycle
o It also transmits the parasite directly to subsequent hosts
• Most commonly known vectors consist of arthropods,
domestic animals, or mammals that assist in
transmitting parasitic organisms to humans or other
Common Vectors
• Mosquitoes serve as
vectors for Malaria,
Dengue fever, Yellow
fever, and Chikungunya
• Ticks can serve as vectors for
Lyme disease, Rickettsia, and
Climate Effects on Disease Vectors
• High temperatures affect both vector and
• Rainfall effects are more complex
o Heavy rainfall and flooding may trigger outbreaks
of diarrhea in areas where crowding and poverty
are present
o Very high rainfall can reduce mosquito populations
by flushing larvae from their habitat in pooled
Increased Malaria Risk
• The IPCC has noted that the global population
at risk from vector-borne malaria will increase
by between 220 million and 400 million in the
next century
• While most of the increase is predicted to
occur in Africa, some increased risk is
projected in Britain, Australia, India and
The Effect of Increased Heat
• Hotter, more humid weather shortens mosquito
breeding cycles
• The incubation of dengue virus is speeded up
by increased temperatures
• Milder winters also allow the survival of many
disease related organisms
o Mosquitos, tics and mice
o Lyme disease, Rocky Mountain spotted fever,
equine encephalitis, anaplasmosis, and bebesiosis
Pesticides and Health
• In the decades of the 1950’s and 60’s, DDT was
widely used to curtail mosquito breeding grounds
• In her 1962 book Silent Spring, the late Rachel
Carson pointed out the tremendous environmental
havoc being wrought by DDT and related compounds
• Current opinion is that curtailing DDT may have
contributed to the current problem, but today’s
problems go well beyond the use of pesticide
Public Health Opinion
• John Balbus, senior adviser for Public Health at the
National Institute for Environmental Health Sciences
siad in an article in the December, 2010 Discover
o “Climate change will cause a worsening of the common
health problems we already see. There will be incremental
changes in the next 5 or 10 years, but that might not
compare to what we’re going to see in a matter of decades.
In trying not to be alarmist, scientists have systematically
underestimated the threat.”
West Nile Virus
• Another vector borne disease is West Nile virus
• It first occurred in Uganda in 1937, with later
outbreaks in Israel in the late 1950’s, and
Romania in 1996
• It has since spread to the U.S., appearing in
New York in 1999
• The vector is Culex pupiens, a common house
Conditions for Spreading West Nile
• West Nile becomes a threat after periods of
hot, dry weather
• In New York in 1999, there was a period of ten
days with temperatures over 100ºF, followed
by heavy rains
• The resulting floods created mosquito breeding
grounds, and populations increased rapidly
• Birds drinking in stagnant pools of water were
Bronx Zoo
• Birds at the Bronx Zoo became infected, with
deaths of several species
o Crows
o Flamingoes
o Bald Eagles
• More than 30,000 West Niles cases have
occurred in the U.S. since 2002, with over
1000 deaths
Infectious Diseases
• Many infectious agents, vector organisms, nonhuman reservoir species, and rate of pathogen
replication are sensitive to climatic conditions
• Salmonella and cholera bacteria, for example,
proliferate more rapidly at higher temperatures,
salmonella in animal gut and food, cholera in water
• In regions where low temperature, low rainfall, or
absence of vector habitat restrict transmission of
vector-borne disease, climatic changes could tip the
ecological balance and trigger epidemics
Dengue Fever in the United States
• Dengue fever was thought to be eradicated in
the U.S., but has been making a comeback
• There are two forms
o Classic dengue fever has been present in northern
Mexico (Matamoros) and is occurring in
Brownsville, Texas
o Dengue Hemorrhagic Fever was seen in
Brownsville, for a resident who contracted the
disease in the U.S., in 2005, and has been
Dengue Hemorrhagic Fever
• The appearance of Dengue Hemorrhagic Fever
in the United States was of great concern
o There is no vaccine to protect against it
o There is no medicine to cure it
• The patient in Brownsville recovered, but
those people who have other health problems
would probably not be so lucky
• Floods are classified as low-probability, high
impact events
• For the decade 1992-2001, there were nearly
100,000 flood related deaths, and 1 to billion
people were affected by flooding
Increased Risk of Floods
• More injuries and deaths due to flooding
• Increased risk of infectious disease due to
flooding, and mental health disease brought on
by flood-related stress
Short Term Flood Effects
• Some health consequences arise during or soon
after the flooding
• These include injuries, communicable
diseases, or exposure to toxic pollutants
• Excessive rainfall facilitates entry of human
sewage and animal wastes into waterways and
drinking water supplies, increasing the risk of
water-borne diseases
Longer Term Flood Effects
• Other effects of flooding may appear later
• These include malnutrition, caused by crop
loss, and mental health disorders resulting
from the stress of flood-related problems
• Droughts represent the other extreme of weather
related precipitation problems
• Globally, disaster effects are greatest for droughts
(and associated famines) because of their regional
extent, which are usually much larger than floodrelated regions
• Another pollutant of concern is "particulate matter,"
also known as particle pollution or PM
• Climate change may indirectly affect the
concentration of PM pollution in the air by affecting
natural or “biogenic” sources of PM such as wildfires
and dust from dry soils
Particulate Matter
• PM is a complex mixture of extremely small particles
and liquid droplets
• When inhaled, these particles can reach the deepest
regions of the lungs
• Exposure to particle pollution is linked to a variety of
significant health problems
• Particle pollution also is the main cause of visibility
impairment (haze) in the nation’s cities and national
Poverty and Disease
• Susan Fisher-Hoch, an epidemiologist at the
University of Texas School of Public Health said,
o “If dengue moves into a population that hasn’t experienced
it and has no natural immunity, we are going to see more
severe disease”
o “The way we live hermetically sealed in our houses – with
screens on the windows and air-conditioning – protects us
enormously. But what about those who don’t live well – the
people in trailer parks sitting on their porches surrounded
by mosquitoes?”
Additional Problems
• According to a paper by McMichael et al.
(2006) in The Lancet, IPCC modeling
indicates a future increase of 5-10% in the
number of malnourished people
• Conflicts over food, together with migrant and
refugee flows likely to result from these widerranging effects would create additional
Anticipated Consequences
• These additional effects include:
o Increase in infectious disease cases
o Malnutrition
o Mental health problems
o Injury and violent death from conflict
The Effects of Climate Change
• The video shows a report that resulted from a
collaboration between the British medical journal,
The Lancet, and University College London

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