Why Does Climate Change?

Why Does Climate Change?

The Sun has a major impact on Earth's climate.
Credit: UCAR

Some factors that have the power to change global climate are natural, like volcanic eruptions and changes in the amount of solar energy. Other factors that are changing climate today are caused by humans, like the addition of greenhouse gases to the atmosphere.

The Sun: Since almost all the energy on Earth comes from the Sun, changes in the cycle of solar activity, called the 11-year sunspot cycle, can cause small changes in Earth’s climate. These changes in the Sun are too small to be the cause of recent climate change. There are also large slow changes to the amount of solar energy that gets to Earth. Over tens to hundreds of thousands of years, changes in the way Earth orbits the Sun have caused large changes in climate such as the Ice Ages.

Volcanic Eruptions: Erupting volcanoes spew red-hot lava and ash into the air. The lava falls to the ground immediately and the ash settles to the ground in a few days. Neither of those have much impact on climate, but there are also tiny particles of sulfur dioxide that spew from volcanic eruptions. They get into the atmosphere and reflect solar radiation back out to space, shading the Earth - causes cooling. The cooling is temporary, lasting usually a year or two. Eventually the particles fall out of the atmosphere to the ground.

Greenhouse Gases: Even though greenhouse gases make up less than 1% of the atmosphere they have a major effect. Greenhouse gases trap heat in the atmosphere through a process called the greenhouse effect. Having some greenhouse gases in the atmosphere is natural. Their heat-trapping abilities keep Earth from being uncomfortably cold. However, the amount of greenhouse gases in our atmosphere has increased over the past 150 years as people burned fossil fuels and changed landscapes, decreasing the amount of forests, which naturally take the greenhouse gas carbon dioxide our of the air as the plants photosynthesize.

Snow and Ice: Because snow and ice are light in color, they have the ability to reflect most of the sunlight that hits them out to space. When snow and ice melt as Earth’s climate warms, less energy is reflected out to space so more lingers around Earth, which causes even more warming.

Other Impacts: There are also other aspects of our planet that have an impact on climate too. Scientists are studying the impact of clouds and tiny particles in the atmosphere called aerosols on climate in hopes of adding more detail to models used to predict future climate. Scientists are also keeping track of how water moves through the world’s ocean. As the amount of sea ice in the Arctic melts, the flow of ocean water could change. Since the water transports heat from place to place this could have a large effect on climate in different regions of the world.

© 2011 NESTA with modifications by UCAR