Earth's changing climate | Earth and society | Middle school Earth and space science | Khan Academy
Have you ever tried to imagine what the world was like in the distant past? Maybe you'd like to explore the age of the dinosaurs, when the Earth was much hotter than it was today. Perhaps you'd prefer when temperatures dropped to much colder than today. You could track a mammoth alongside our early ancestors, who evolved around the end of the last ice age.
We know about all of these ancient climate trends because scientists learned how to estimate them using evidence from ice cores, tree rings, and other natural phenomena. We now know that for most of human history, people could expect a pattern that looks something like this graph from the National Aeronautics and Space Administration, which shows how temperatures changed each year in comparison to this line, which represents the average global annual temperature from 1880 to 1899.
When we look at the time period between 1880 and 1940, we can see that some years temperatures would be higher than this average, some years they would be lower, but they generally swing back to a pretty comfortable state. Around the 1950s, though, the global average temperature began to climb to unprecedented levels. Our ancient temperature records never showed such a sudden increase.
When we look at the time period from 1950 to today, we can see that while temperatures still swing back down some years, these colder years are still much hotter than the average temperatures in the past. Researchers noticed a change in the concentration of greenhouse gases in the Earth's atmosphere. These greenhouse gases trap heat from the sun in our atmosphere, similar to how a greenhouse allows sunlight to pass through its glass walls but prevents the heat it creates from leaving.
This greenhouse effect is what keeps our planet warm and habitable enough for life. However, the amount of one particular greenhouse gas was rising: carbon dioxide, or CO2. CO2 is naturally one of the most notable greenhouse gases besides water vapor, but we can also release CO2 by burning wood or fossil fuels like coal and oil. Over time, humans have increasingly relied on these fuels to power things like planes, cars, and trains, as well as to generate electricity.
As a result of these human activities, more CO2 is being released into the atmosphere than ever before—much more than is normally released by the Earth and at a much faster rate. The increasingly heavy blanket of greenhouse gases is trapping excess heat in our atmosphere rather than allowing more of it to radiate into space as normal. This is what's causing Earth's average temperature to rise beyond what scientists would expect based on historical patterns.
While scientists once referred to this process as global warming, most now prefer the more general term climate change. A world that's a little bit warmer on average might not seem like such a big deal, but we've learned that even a small shift in the planet's natural processes can have drastic consequences.
When studying the early signs of climate change, scientists predicted that as cold places like the North and South Pole got warmer, the ice would begin to melt. All of that frozen water suddenly flowing into the oceans would cause sea levels to rise, which would affect the planet's weather system. Have you heard all the news about weird weather in the past few years? Snow in places that are usually warm and dry, or drought in places that are usually cold and rainy? Huge fires during extremely hot summers, severe storms battering coastlines, and flooding cities.
Many of these natural hazards used to be somewhat rare, but now they're becoming more common, exactly as climate scientists predicted. People have relied on relatively consistent weather patterns for generations, so they aren't prepared to adapt to these changes in their local environment. Communities that are already feeling the effects of climate change are worried that they're going to lose their homes, their livelihoods, or their sources of food and water.
Scientists are working on technologies that can help us remove some of the excess CO2 from the atmosphere, but in the meantime, they recommend that we emit less CO2 in the first place. This would allow us to limit how much the global average temperature increases, giving communities time to adapt to changes in their surroundings.
Of course, it's complicated to change the way our societies work to help reduce CO2 emissions. You may see some people advocating for tweaking individual behaviors like eating plant-based diets or using low-carbon transportation methods. You may see others saying that since large organizations and highly populated countries emit the most CO2, we need to push them to make more wide-ranging institutional changes.
As someone who works in environmental science, I know that sorting through all of these different facts and opinions on climate change can be overwhelming. It's difficult to think about living in a world that may be very different from what I've always known. In the past, I've found it helpful to both adopt simple sustainable habits in my own life while also seeking out community groups that work on bigger initiatives.
It's easier to imagine the future when you help others to shape it. Now that we've taken some time to think about Earth's past and what's happening to it in the present, try looking towards the future of our planet. What is your ideal future, and how can you help to make it happen?