Earth (Image Source: NASA)

Climate change can occur naturally. Our climate is controlled by a balance between energy received from the sun and radiation the Earth loses to space. Any changes in our environment, either natural or human-induced, that alters this balance can affect our climate.

Natural factors:

• changes in solar activity
• changes in Earth's orbit
• natural greenhouse effect
• natural atmospheric aerosols
• volcanic emissions

Human-induced factors:

• enhanced greenhouse effect
• land use change
• enhanced atmospheric aerosols

The Earth's natural thermostat...

The Earth's temperature is regulated by a natural system known as the 'greenhouse effect'. Naturally occurring greenhouse gases, such as water vapour, CO₂, methane, nitrous oxide, and ozone, trap radiation in the atmosphere which helps to keep the Earth warm enough to support life. Problems can arise when the concentrations of these naturally occurring gases are increased and new greenhouse gases like chlorofluorocarbons (CFCs) are added to the system.

Radiation and the atmosphere (Data from Environment Canada, 1994)

Did you know?
Without the Earth's natural greenhouse effect the average temperature of the Earth would be -18°C.

Carbon is a part of the Earth's natural system. Within the Earth, it is present as fossil fuels and in sedimentary rocks. It is also stored at the Earth's surface in vegetation and soil, and in the oceans as inorganic carbon dissolved in the sea water. In the atmosphere, carbon occurs mainly as carbon dioxide (CO₂). Before the Industrial Revolution, CO₂ and other greenhouse gases such as methane (CH₄),that were put into the atmosphere were balanced by processes of natural removal, so atmospheric concentrations of these gases did not vary much.

Did you know?
Greenhouse gases accumulate in the atmosphere because their molecules have life spans of decades or even centuries.

Since the start of the Industrial Revolution in the 1700s, atmospheric concentrations of CO₂ have increased by 30%. Climate scientists predict that over the next 40 to 60 years these concentrations will double from their pre-industrial levels. The primary cause of the expected buildup of CO₂ is from human activities.

Trends in methane and CO2 concentrations (Environment Canada, 1999a)

Did you know?
Human activity is currently responsible for emitting 30 million tons of CO₂ each year, 12 million tons of which accumulate in the atmosphere.