In short: it is the natural process that warms the Earth’s surface.
The process is called the greenhouse effect because the exchange of incoming and outgoing radiation that warms the planet works in a similar way to a greenhouse.
Picture this: a greenhouse is so successful at growing plants year-round, even when it’s too cold outside for some plants to typically thrive. How? Because the air inside the greenhouse naturally stays warmer than the air outside.
A greenhouse is constructed of glass, allowing sunlight to penetrate the exterior and warm the air and plants inside. The heat that isn’t absorbed by plants is trapped by the glass and can’t escape. Throughout daylight hours, sunlight keeps coming through the glass, adding more and more heat energy so the inside gets warmer and warmer (and continues to stay warm after the sun sets).
The Earth and the Sun work in a similar fashion (on a much more massive scale and a different physical process). The sun shines through the Earth’s atmosphere and the earth’s surface warms up. Some of the Sun’s energy is reflected directly back to space, the rest is absorbed by land, ocean, and the atmosphere. The greenhouse gases in the atmosphere trap heat radiating from Earth toward space.
What is Global Warming? feat. Katharine Hayhoe
So, what is global warming? This adorable animation makes it super simple.Posted by Climate Reality on Saturday, June 4, 2016
But here’s where this process presents a problem:
Carbon dioxide, methane, and other “greenhouse gases” trap heat that would otherwise escape Earth’s atmosphere. In the right proportion, these gases do a critical job ensuring the atmosphere holds onto enough heat to support every kind of life on the planet. Without them, the Earth would lose so much heat that life as we know it would be impossible.
The problem arises when greenhouse gas levels get too high because of human activities, trapping too much of the sun’s energy as heat and upset the natural systems that regulate our climate. Things keep getting hotter and hotter and we start seeing more and more extreme weather and other impacts.
Even small changes in the global average temperature can cause major and dangerous shifts in climate and weather. Just consider the difference between 0 and 1 degrees Celsius (or 32 and 33 degrees Fahrenheit) – that one degree means the difference between ice and water.
Now imagine that difference happening regularly for months. Imagine it happening in a region that depends on a natural cycle of winter snow building up and precipitation in the spring, feeding streams and rivers and supplying farms and communities with the water they need for everyday life. And that’s just one example.
Plus, burning fossil fuels aren’t the only thing contributing to rising levels of carbon dioxide. Trees are often called the Earth’s lungs, thanks to their incredible ability to absorb and store carbon dioxide from the atmosphere. Deforestation – cutting down trees on a large scale for fuel, land, or other purposes – leads to more greenhouse gases in the atmosphere as more trees are burned and fewer are in the ground to absorb excess carbon dioxide.
How big of a deal is this?
We are seeing our world transformed by climate change and if we do nothing, that transformation will be profound. We call this transformation – the process of climate change and its many effects on our world – “the climate crisis.”
The Earth has experienced cycles of warming and cooling in the past, but experts believe the current warming trend is "proceeding at a rate that is unprecedented in the past 1,300 years."
What can we do?
Start by burning less fossil fuels. Ultimately, we need to work to stop burning fossil fuels altogether, which means a global shift to clean energy technologies like solar and wind. Learn more about renewable energy with our fact sheet and learn how you can take action against the climate crisis.