Metzger_Ice Ages

1 WHAT CAUSES ICE AGES? What is an ice age? An ice age is a period in Earth's history when the ice on the polar caps significantly expands due to a lowering of the Earth's global temperatures. Over the course of millions of years, scientists believe that the Earth has experienced at least five major ice ages. During these periods land in North America and Northern Europe were covered by giant ice sheets and glaciers. Earth is currently in an ice age called the Quaternary Ice Age which began around 2.5 million years ago and is still going on. We are currently in an interglacial stage of this ice age. The periods within ice ages are defined as: INTERGLACIAL PERIOD GLACIAL PERIOD Glacial - A glacial period is a cold period when the glaciers are expanding Interglacial - A warming period when the glaciers and ice sheets are receding

2 What causes an ice age? The Earth is constantly undergoing changes. These changes can impact the global climate. Some of the changes that can influence an ice age include: Earth's orbit - Changes in the Earth's orbit (called Milankovitch cycles) can cause the Earth to be closer to the Sun (warmer) or further from the Sun(colder). Ice ages can occur when we are further from the Sun. There really is no simple answer to the question of why ice ages occur; there are many different and interconnected causes. In general, it is felt that ice ages are caused by a chain reaction of positive feedbacks triggered by periodic changes in the Earth’s orbit around the Sun. These feedbacks, involving the spread of ice and the release of greenhouse gases, work in reverse to warm the Earth up again when the orbital cycle shifts back. The last ice age ended about 12,000 years ago. The next cooling cycle would be expected to start about 30,000 years or more into the future. Many theories have been proposed to explain the causes of ice ages. Any credible theory must explain what caused the ice to build up, how and why the ice advanced and retreated at different times during a glaciation and why the ice eventually disappeared. One theory that tries to explain these phenomena is the Ocean–Control Theory . The diagram on the next page illustrates this theory. of energy output by the Sun also changes . Low cycles of energy output Solar Energy-hosity help in producing an ice age . Atmospheric composition - Low levels of greenhouse gasses such as carbon dioxide can cause the Earth to cool leading to an ice age . can have a great impact on the Earth's climate . Changes in currents can carse Ocean currents - ice sheets to build up . introduce huge amounts of carbon dioxide into the atmosphere . The lack of volcanoes can Volcanoes - cause an ice age . Increased volcanic activity can put an end to an ice age as well .

4 Questions for discussion 1. Could the ice age formation process be considered a cycle? Explain why. 2. What is the major controlling factor for the Earth’s heating and cooling system according to this theory? 3. How is it possible for a major warming trend rather than a cooling trend to bring about an ice age? 4. Why would cold runoff be considered a negative feedback in the glacial formation process? res the ice age inte Page a fan been consider spac Because ene interglacial The earth's major factor in controlling heating and cooling is the oceans it has sunlight in more quantity causing evaporation in the ocean . A major warming trend rather than cooling trend brings about an ice h age because the temperature is so hig carsing the earth to need to cool down causing glaciers to form and when they melt it will start an ice age . Cold runoff is considered a negative feedback in the glacial formation and this is because it is not a major climatic change the cold runoff makes the oceans colder and as a result less evaporation and less precipitation occur .

5 CO2 Does Not Drive Glacial Cycles Anthony Watts / February 21, 2009 Guest post by Steven Goddard There are still people who insist that changes in CO2 can explain the pattern of glacial and interglacial periods. This article will present several arguments demonstrating that is incorrect, based on the ice core data below. The most obvious reason is that CO2 lags temperature. Changes in ocean temperature have driven the changes in atmospheric CO2, as explained here. CO2 is not the driver. Now consider the earth 20,000 years ago. Temperatures were low – about 8C cooler than the present. Due to the cold ocean temperatures, levels of atmospheric H20 (the primary greenhouse gas) were low. CO2 levels were also low, at about one half current levels. The earth’s albedo was very high due to extensive ice cover which had much of North America and Europe buried in ice. Using the popular “CO2 and feedbacks explain everything” theory, all of these negative feedbacks should have driven earth further and further into an irrecoverable ice age. Cold ocean water should have continued to absorb more CO2 from the atmosphere. Atmospheric H2O should have continued to decline due to lower vapor pressures over the cooling oceans. Albedo should have continued to increase due to expanding glaciers further from the poles. All of these negative feedbacks should have caused temperatures to decrease further, and the death spiral should have continued. But none of these things happened. Instead, the earth warmed very quickly. CO2 was absolutely not the driver, and positive/negative feedbacks had to be in balance. Consider the earth 14,000 years ago. CO2 levels were around 200 ppm and temperatures, at 6C below present values, were rising fast. Now consider 30,000 years ago. CO2 levels were also around 200 ppm and temperatures were also about 6C below current levels, yet at that time the earth was cooling. Exactly the same CO2 and temperature levels as 14,000 years ago, but the opposite direction of temperature change. CO2 was not the driver. Now consider 120,000 years ago. Temperatures were higher than today and CO2 levels were relatively high at 290 ppm. Atmospheric H20 was high, and albedo was low. According to the theorists, earth should have been warming quickly. But it wasn’t – quite the opposite with temperatures cooling very quickly at that time. CO2 was not the driver. If CO2 levels and the claimed lockstep feedbacks controlled the climate, the climate would be unstable. We would either move to a permanent ice age or turn into Venus. Warmer temperatures generate more CO2. Increased CO2 raises temperatures. Warmer temperatures generate more CO2 …… etc. It would be