Page 14 - SGG_220316_Teachers_Handbook_Module_7

4.1. Natural changes to the climate

The leading cause of climate change is human activity -including release of greenhouse gases.
However, there are lots of natural causes that also lead to changes in the climate system. Some of
these natural cycles include:

Milankovitch cycles

As Earth travels around the sun, its path and the tilt of its axis can change slightly. These changes, called
Milankovitch cycles, affect the amount of sunlight that falls on Earth. This can cause the temperature
of Earth to change. However, these cycles take place over tens or hundreds of thousands of years and
are unlikely to be causing the changes to the climate that we are seeing today.

El Niño Southern Oscillation (ENSO)

ENSO is a phenomenon of changing water temperatures in the Pacific Ocean. In an 'El Niño' year, the
global temperature warms up, and in a 'La Niña' year, it cools down. These patterns can affect the
global temperature for a short amount of time (months or years) but cannot explain the persistent
warming that we see today.

Natural forcings that can contribute to climate change include:

Solar irradiance

Changing energy from the sun has affected the temperature of Earth in the past. However, we have
not seen anything strong enough to change our climate. Any increase in solar energy would make the
entire atmosphere of Earth warm, but we can only see warming in the bottom layer.

Volcanic eruptions

Volcanoes have a mixed effect on our climate. Eruptions produce aerosol particles that cool Earth, but
they also release carbon dioxide, which warms it. Volcanoes produce 50 times less carbon dioxide than
humans do, so we know they are not the leading cause of global warming. On top of this, cooling is the
dominant effect of volcanic eruptions, not warming.

Natural climate cycles can change the temperature of Earth, but the changes we are seeing are
happening at a scale and speed that natural cycles cannot explain.

4.2. Human causes of climate change

Greenhouse gases trap the Sun's heat in Earth's atmosphere. It's normal for there to be some
greenhouse gases in our atmosphere. They help keep Earth warm enough to live on. But too many
greenhouse gases can cause too much warming.

When looking at all the evidence, there is a large scientific consensus that humans are the leading
cause of climate change. In their latest report, the Intergovernmental Panel on Climate Change stated

This project has been funded with support from the European Commission. This communication reflects the
views only of the author, and the Commission cannot be held responsible for any use which may be made of the

information contained therein.