Geological records of the past millions of years show some large changes in the climate. The Earth’s climate can be influenced by natural causes that are outside of the climate system, which include changes in solar output, volcanic activity, and our planet’s orbit around the Sun.
Changes in our climate have been occurring for millions of years, for many different natural factors that scientists are just starting to understand better. The dilemma climate specialists face in the short-term is to separate natural climate variability from anthropogenic climate change.
Natural causes of climate change
- Volcanic Activity
Volcanic activity is well known to change the climate. Climate data from volcanic events indicate that just one large eruption is enough to cause global cooling of around 0.3°C and between 1 and 2 years.
Volcanic eruptions can release large quantities of dust and other gases (such as sulphur dioxide) into the atmosphere. Particles from the eruption spread gradually over the globe blocking 5-10% of the sun’s energy.
Such a cooling event has been noticed in the global temperature record after of the eruption of Mount Pinatubo in June 1991 that released 20 million tones of sulphur dioxide into the atmosphere. The climate change related to individual eruptions is, however, short-termed compared to other natural influences. The temperature anomaly caused by a single volcanic eruption is unlikely to persist and lead to significant long-term climatic changes.
- Solar Output
The main source of Earth’s heat is the Sun, so even small variations in solar output can have an impact on the climate. Researchers monitor these changes by observing sunspots and (more recently) satellite measurements.
When there is an increase in sunspots, solar output also increases. Scientists at the University of Washington have determined that at the peak of the 11-year solar cycle, increased solar output causes a sudden warming of the atmosphere of 0.16 °C.
- Orbital Changes
Changes in the Earth’s orbit mean that the distance between the Earth and Sun varies over a long period of time, causing frequent variations in the total amount of solar energy reaching our planet. These variations affect terrestrial climate change and the characteristic frequencies are known as Milankovitch cycles.