Natural vs anthropogenic climate change

Climate change is any change occurring to the planet's climate either permanently or lasting for long periods of time. It is the cumulative total of two related sources: anthropogenic climate change and natural climate change. Anthropogenic climate change is defined by the human impact on Earth's climate; while natural climate change are the natural climate cycles that have been and continue to occur throughout Earth's history.

Natural Climate Change

Earth’s climate has always been driven by the amount of incoming and outgoing energy. Without the influence of humans, the Earth has natural cycles that drive the climate. The major factors contributing to Earth’s natural climate change are determined by:

• the Earth's orbit around the sun,
• the output of energy from our sun,
• the ocean’s natural cooling and warming cycles, and
• the constant variability in volcanic activity.

Another factor to consider are the glacial advances and retreats that occur throughout Earth’s history. In the last 650,000 years, there have been around seven ice ages, the most recent ending around 12,000 years ago. Since then, the Earth has experienced a glacial advance known as the little ice age, which occurred from the 16th century through to the 19th century. However, Earth is still in the natural warming process from this glacial advance and many climate change deniers erroneously claim that this is the cause for the current dramatic climate changes. Although natural climate factors have some effect on the current global warming, they are not as pronounced as human induced factors.

Anthropogenic Climate Change

Human induced climate change is directly linked to the amount of fossil fuels burned, aerosol releases, and land alteration (from agriculture and deforestation). The beginning of the Industrial Revolution shows a major spike in temperature levels and climate influences. The product of fossil fuel burning is the emission of a greenhouse gas: carbon dioxide, which traps heat. Climate change is generally associated with global warming. However, some small areas (such as the tropical Pacific) show that the release of aerosols into the atmosphere the area has actually cooled the region, or at least slowed the warming.

Figure 1 below is a video that shows how carbon dioxide levels over the last 400,000 years have stayed below 300 ppm, and skyrocketed in the 1950's.

Figure 1. Before the Industrial Revolution, the climate change was caused by natural factors. But, the current climate change is largely due to anthropogenic causes.

Video credit: NASA. Data source: NOAA/WDS.

Some noticeable evidence occurring from anthropogenic climate change include:

• the overall sea level rise,
• temperature rise,
• melting ice sheets and glaciers,
• increased extreme events, such as hurricanes getting stronger, and
• ocean acidification.

The oceans naturally rise as glaciers and snow covers melt, however compared to the last century, the rate of rise in the last decade is approaching twice as much. Figure 2 below is a video showing how the Earth has been warming past few decades, and warming is expected to continue for the rest of the 21st century.

Figure 2. Global temperature changes since 1880, relative to 1951-1980.

Video credit: NASA/Scientific Visualization Studio.

For Further Reading

• Anthropogenic climate change
• Natural climate change
• Axial tilt
• Solar energy to the Earth
• Modes of climate variability
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