Climate Change

Causes Several factors affect global climate: 1.Changes in solar output 2.Changes in Earth's orbit 3.Changes in the distribution of continents 4.Changes in atmospheric greenhouse gases.

1. Change in Solar Output The amount of energy the sun emits changes Major changes occur in 11-year cycles CONCLUSION: The impact from variations in solar output is minimal (~1%) See movie

2. Changes in Earth’s orbit Over long periods of time, Earth’s orbit around the sun changes. Eccentricity: shape of Earth's orbit around the sun changes Obliquity: Earth's axial tilt changes Precession: direction of Earth’s rotational axis wobbles. These changes impact how and when sunlight hits the Earth. See animation

Milankovitch Cycle

3. Changes in distribution of landmasses Lots of evidence suggests that Earth’s continents move over millions of years. Consequences: 1.Changes in distribution of landmasses change ocean and wind currents 2.When landmasses are closer to polar regions, snow and ice accumulate. ?v=uGcDed4xVD4

Changes in distribution of landmasses

4. Changes in Atmospheric Content The Earth is wrapped in a layer of different gases held in place by Earth’s gravity. Some of those gases allow visible light from sun through, but prevent infrared radiation from Earth from reflecting back into space. –Greenhouse gases Without greenhouse gases, the Earth’s average temperature would be -18  C

Greenhouse Effect -103 W / m W / m W / m 2 Some of the radiation from the sun is reflected off atmosphere and surface; the rest is absorbed by the Earth. The Earth emits some of the radiation back into space. Some of this radiation is reflected back to Earth by greenhouse gases.

Changes in Atmospheric Content Water vapor is the most abundant greenhouse gas on Earth. Carbon dioxide is another.

Past climate? How do we know about past atmospheric data if no one was there? How do we know about past climate?

Climate proxies Historical records Ice cores Bore holes Lake sediment Ocean sediment Caves Fossils Plankton Distribution of animals Pollen Tree rings Distribution of plants

What’s the fuss about? Earth has and will continue to have variable climates. The Earth is not fragile; the zone of habitability for humans is. Science & Politics Do something! Humans play a role in climate change. We need to find a way to minimize greenhouse gas emissions. If we do nothing now, it may be too late to fix it later. Do nothing! Climate change is complex Minimizing greenhouse gas emissions will be prohibitively expensive. If we do something, it may cripple the economy.

Questions?

Ice Cores Deep ice cores are analyzed to infer past climate. Different layers contain different types and amounts of trapped gas ratios of stable isotopes pollen

Rate of sedimentation through time. + = warmer summers  = cooler summers Charcoal indicate past fire events. Remains of microorganisms indicate changes in past climate each species has a limited range of habitable conditions. Sediment Cores