Climate Variability
You are taught that "climate is what you expect and weather is what you get". This implies that climate does not change.
However, Earth's history tells us that global climate has always changed. Using a variety of proxy records that help us infer global temperature and moisture. These records include ice-cores, deep ocean sediments and geologic records. These records are far more limited than observations of temperature and precipitation as taken today. However, when viewed collectively they help paint a depiction of climate variability through time.
http://environment.nationalgeographic.com/environment/global-warming/gw-impacts-interactive/
Global Temperature of the past 500+ million years
A chronology of global temperature reconstructed from a variety of records shows us several things
(1) The Earth has generally been warmer than present for the past 500 million years, with some periods being up to 6-8 degree Celsius warmer.
(2) Long-term climate variability operates on very long time scales, with millions of years passing as temperature rises and falls
(3) Long term global cooling has been observed generally for the past 55 million years.
(4) For the past 3 million years or so, more frequent variability has been observed featuring cool periods (called glacial period) and warm periods (called interglacial periods, such as today).
(5) For the past 1 million years, a 100,000 year cycle between glacial periods.
(6) The last glacial period ended around 18,000 years ago, during which the Earth was around 6C cooler than present.
(1) The Earth has generally been warmer than present for the past 500 million years, with some periods being up to 6-8 degree Celsius warmer.
(2) Long-term climate variability operates on very long time scales, with millions of years passing as temperature rises and falls
(3) Long term global cooling has been observed generally for the past 55 million years.
(4) For the past 3 million years or so, more frequent variability has been observed featuring cool periods (called glacial period) and warm periods (called interglacial periods, such as today).
(5) For the past 1 million years, a 100,000 year cycle between glacial periods.
(6) The last glacial period ended around 18,000 years ago, during which the Earth was around 6C cooler than present.
What do we know about the causes of changes we have observed over the geologic record?
Long-term changes in global climate that occur on timescales of millions of years are associated with geologic and tectonic factors. Warm periods in the planet's past have been linked to active periods of tectonic activity featuring seafloor spreading and long term outgassing of carbon from the solid Earth. Atmospheric carbon dioxide levels during some of these periods were extremely high, likely in excess of 1000 parts per million, compared to 280 parts per million CO2 in 1850 and nearly 400 parts per million in 2013. How do you think such high levels of atmospheric CO2 would have influenced climate directly, and indirectly? For indirect effects you will have to consider feedback processes.
Changes in climate observed over the last three million years are tied to changes in orbital cycles as discussed in Module 3. Glacial periods correspond to favorable orbits for glacial growth featuring low amount of solar radiation in the northern hemisphere summer near the periphery of the ice sheets (~ 65-degrees North latitude). Positive feedback processes including the ice-albedo feedback, water-vapor feedback and others facilitate the 6-degree change in global temperature between glacial and interglacial periods. Without these feedbacks the magnitude of the change would be quite small.
Log in to BBLearn, and under Module 8, go to the Mastering Assignments. Complete "Assignment 8.1: Measuring Climate Change."
Long-term changes in global climate that occur on timescales of millions of years are associated with geologic and tectonic factors. Warm periods in the planet's past have been linked to active periods of tectonic activity featuring seafloor spreading and long term outgassing of carbon from the solid Earth. Atmospheric carbon dioxide levels during some of these periods were extremely high, likely in excess of 1000 parts per million, compared to 280 parts per million CO2 in 1850 and nearly 400 parts per million in 2013. How do you think such high levels of atmospheric CO2 would have influenced climate directly, and indirectly? For indirect effects you will have to consider feedback processes.
Changes in climate observed over the last three million years are tied to changes in orbital cycles as discussed in Module 3. Glacial periods correspond to favorable orbits for glacial growth featuring low amount of solar radiation in the northern hemisphere summer near the periphery of the ice sheets (~ 65-degrees North latitude). Positive feedback processes including the ice-albedo feedback, water-vapor feedback and others facilitate the 6-degree change in global temperature between glacial and interglacial periods. Without these feedbacks the magnitude of the change would be quite small.
Log in to BBLearn, and under Module 8, go to the Mastering Assignments. Complete "Assignment 8.1: Measuring Climate Change."