Natural Causes of Climate Change

• Ice Core - The level of carbon dioxide has naturally risen and fallen in cycles over time.  Cores removed from ice sheets show different layers of time. Good accuracy but limited to local areas. Hard to know how much change was due to temperature rather than rain/ sunlight. Shows how ice melts and how ice melted due to global warming. 
• Tree Rings - The thickness of rings in trees depends on the climate. In warm years trees have wide rings. Shows climate conditions have changed over times and how tree work. Reliable as CO2 levels and isotopes correlate with each other. However there could be slight dating errors. It is reliable as it shows CO2 over the years and can be used to trace how life and the earth was. 
• Historical Records - Pictures and written accounts from different locations through history. Show’s evidence of cooler periods in time and warmer periods (Greenland accessible and lived in)s. They are usually just looking at one place in time, not the whole world. Pictures can be misleading.  Physical records showing how the world was and how it changed overtime. 
• Greenhouse effect – natural process by which the earth’s atmosphere warms and keeps the planet habitable