What causes climate change?
Greenhouse Gases & the Greenhouse Effect
Greenhouse gases (GHGs) are gases in Earth's atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere.3 The greenhouse gas with the greatest impact on warming is water vapor. But it remains in the atmosphere for only a few days. Carbon dioxide (CO2), however, persists for much longer. It would take hundreds of years for a return to pre-industrial levels. Other greenhouse gases such as methane and nitrous oxide are also released through human activities but they are less abundant than carbon dioxide.1
The following video below shows the impacts of greenhouse gases on Earth and how the greenhouse effect works.
As the video states, CO2 occurs naturally in the atmosphere and is a vital part of life on Earth. Humans and most animals breathe in air to receive oxygen and breathe out CO2. Plants then use CO2 to help them grow through photosynthesis, keeping the carbon and releasing the oxygen.
This is why you hear about the important of trees in addressing climate change. Trees store, or sequester, carbon from the atmosphere. Deforestation, or the permanent removal of trees for use other than a forest, and the subsequent burning of trees releases their stored carbon back into the atmosphere.8 This vast amount of carbon storage without releasing it back into the atmosphere for a given time makes forests what is a called a ‘carbon sink.’ A carbon sink is anything that absorbs more carbon than it releases as carbon dioxide.5
Trees aren’t the only natural method of carbon sequestration, though. Similar to the plants in forests, the plant life in the ocean also creates oxygen while sequestering carbon from the atmosphere. Oceans produce roughly 50% of the oxygen we breathe on Earth while sequestering about 30% of the carbon emitted by human activity.10,11 Although helpful in addressing a portion of the challenge of excess CO2 in the air, as the ocean tries to pick up the slack from humans, it is leading to ocean acidification, explained further in section entitled “What are the impacts of climate change?” below.
The video also covers the concentration of CO2 in the atmosphere, mentioning 400 parts per million, or 400ppm. As of the end of 2020, NASA scientists and other climate scientists measure the current concentration of CO2 in the atmosphere to be 415ppm, seen in the graph below.
This graph only shows the CO2 concentrations in the atmosphere after 2004, with the average seasonal cycle removed to better help display the concentration increase. The graph below zooms out from the one above to show the CO2 concentration in atmosphere for the past 800,000 years, as studied in the bubbles of air captured in the layers of ice from Antarctica. This graph shows the huge spike in CO2 concentration after 1950 and was one of the first alarming visuals to help prove to the world the impacts humans are having on the climate systems on Earth. It’s aptly known as the ‘hockey stick’ graph for how the spike in CO2 concentrations in recent years sticks up like the blade of a hockey stick after thousands of years of relatively stable concentrations.9
The NASA video above also briefly mentions the misconception that the Earth being only a few degrees warming won’t have a big impact on the planet. Going back to the determination of weather vs. climate, a few degrees of temperature difference in a day may not mean much, but a few degrees of average temperature difference across the entire globe leads to massive consequences. The following video and illustration help explain the impacts just a few degrees can have on the world.