What is climate change?

Dr Kyle Clem from Te Kura Tātai Aro Whenua—School of Geography, Environment and Earth Sciences answers:

"One of the most useful parameters we use to understand the global climate is the global average temperature, and there’s only two things that cause changes in the global average temperature, and that’s the brightness of the sun and the composition of gases in our atmosphere.

"Over the past couple hundred years, Earth’s global average temperature has been warming but we have not been seeing an increase in energy from the sun, and this points to changes in the composition of gases in our atmosphere.

"A very, very small percentage of Earth’s atmosphere is comprised of potent gases called greenhouse gases. Now as Earth’s average temperature has warmed over the past couple hundred years, we’ve also seen an increase in these greenhouse gases such as carbon dioxide and methane, and the amount of added heat to Earth’s climate system from this increase in greenhouse gases is consistent with the warming that we’ve seen in Earth’s climate.

"So, we know that we’re not getting more energy from the sun, and the concentration of greenhouse gases are increasing, so the last remaining question is where are these greenhouse gases coming from? While we’ve seen an increase in carbon dioxide, we’ve also seen a steady decline in oxygen in the atmosphere. That tells us that we are burning carbon-rich substances which takes in oxygen. The carbon in the atmosphere that’s increasing is non-radioactive which also tells us that it’s been stored away underground away from the sun for millions of years, and therefore recent climate change is actually caused by human activity—and that’s called anthropogenic climate change."

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