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 inter-governmental 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)