The phrase “global warming” hasn’t been around long, but climate change, as it’s also known, is nothing new. In fact, it has been a constant throughout history. Earth’s climate today is very different from what it was 2 million years ago, let alone 10,000 years ago. Here are the key terms that are crucial to understanding global warming:

  • Carbon cycle: The natural system that, ideally, creates a balance between carbon emitters (such as humans) and carbon absorbers (such as trees), so the atmosphere doesn’t contain an increasing concentration of carbon dioxide. (Concentrations of carbon dioxide in the atmosphere are expressed as parts per million, or ppm.)

  • Carbon sinks: Anything that absorbs carbon dioxide from the atmosphere and stores carbon. The ocean, trees, and soil are all carbon sinks.

  • Fossil fuels: Fuels, such as oil and coal, that are made from the fossils of old plants, which have taken hundreds of thousands of years to form underground.

  • Intergovernmental Panel on Climate Change (IPCC): An international body of the United Nations, composed of over 2,000 scientific experts. The IPCC compiles peer-reviewed climate science to create an objective source of climate information.

  • Kyoto Protocol: The international agreement under the United Nations to reduce global greenhouse gas emissions from industrialized countries by 5.2 percent below 1990 levels by the year 2012. The Protocol is ratified by 177 countries.

  • Renewable energy: A continual source of energy, such as energy from the sun, wind, flowing water, heat from the Earth, or movement of the tides.