Transcript How has Toronto`s climate changed in the last 150 years?

Evidence for Climate Change
Key Ideas – Climate Change Evidence
• No single study or observation is proof of climate
change (natural or human-caused);
• A large body of evidence supports the hypothesis
that the earth’s climate is changing, and that human
activities are contributing to climate change;
Key Sources of Physical Evidence
•
Evidence: direct weather and climate observations,
computer simulation, observations of ecological
systems and biological species (i.e. plants and animals)
1. Rising Temperatures
• Weather stations have recorded daily temperatures
since the late 1800s, average global temperature
calculated from these records. As of 2006, 11 of the
previous 12 years were the warmest ever recorded.
• Warming is not even over the globe:
• Canada’s average temperatures have increased by 1 °C
in the last 55 years, but by as much as 2.5 °C in some
parts of the Yukon.
Intergovernmental
Panel on Climate
Change (IPCC): a
scientific intergovernmental body that
shared the 2007 Nobel
Peace Prize with Al
Gore.
People from over 130
countries – more than
2500 scientific expert
reviewers - contributed
to the IPCC Fourth
Assessment Report
(2007).
2. Melting Glaciers, Ice Sheets and Sea Ice
• The average size of glaciers has begun to decrease.
Glaciers are important because they:
are sources of drinking water for nearly half the people
around the world. Melting could cause serious
freshwater shortages.
• Ice sheets in Greenland and Antarctica are disappearing.
Arctic sea ice also disappearing.
• Ice sheets: ice on land, melting causes larger increase in
sea level
• Sea ice: ice floating on water
3. Rising Sea Level
Small increases can result in floods for low-lying countries
(e.g. the Maldives)
Sea level rises are caused by:
• Glacier and ice sheet melting leads to water running into
the ocean
• Thermal expansion: water expands slightly when it
warms up
4. Changes in Severe Weather
Increased frequency and intensity of severe weather
events:
Heat waves, hurricanes (the # of category 4 or 5 hurricanes
have doubled over the last 40 years)
5. Changes in Precipitation Patterns
More heavy precipitation events
More drought in other areas (southern Africa, southern
Asia)
Bangkok, Thailand - 2011
Texas - 2011
5. Changes in Ecosystems
Plants and animals respond to changes in temperature and
precipitation –
Earlier flowering and breeding;
Undesirable insects and plants moving north into new
regions
Ecosystem Impacts: Coral Reef Bleaching
Ecosystem Impacts: Migration of Species
“Warming of the climate system is
unequivocal.”
(Intergovernmental Panel on Climate Change, Fourth
Assessment Report, 2007)
“Most of the observed increase in global
average temperatures since the mid-20th
century is very likely (>90% certain) due
to the observed increase in
anthropogenic greenhouse gas
concentrations.”
(Intergovernmental Panel on Climate Change, Fourth
Assessment Report, 2007)