How Do We Know The Earth Is Getting Warmer ?




The sky is still blue. Trees are still green. Wind still blows. Clouds are still white and fluffy. Rain still pours from the sky. Snow falls and it still gets really cold sometimes in some places. Earth is still beautiful.
So what is the problem? What is the fuss about climate change and global warming?
Well, after observing and making lots of measurements, using lots of NASA satellites and special instruments, scientists see some alarming changes. These changes are happening fast—much faster than these kinds of changes have happened in Earth's long past.

Global air temperatures near Earth's surface rose almost one and one-half degrees Fahrenheit in the last century. Eleven of the last 12 years have been the warmest on record. Earth has warmed twice as fast in the last 50 years as in the 50 years before that.
One and one-half degrees may not seem like much. But when we are talking about the average over the whole Earth, lots of things start to change.


Why is Earth getting warmer?

Why is Earth getting warmer? Here's one clue: As the temperature goes up, the amount of carbon dioxide, or CO2, in the air goes up. And as the carbon dioxide goes up, the temperature goes up even more.
Carbon dioxide is a greenhouse gas. That means it traps heat from Earth's surface and holds the heat in the atmosphere. Scientists have learned that, throughout Earth's history, temperature and CO2levels in the air are closely tied.

Line graph show carbon dioxide levels over the past 400,000 years. Shows sharp increase starting around 1950.
This graph shows carbon dioxide levels over the past 450,000 years. Notice the sharp increase starting around 1950.
This graph shows CO2 levels over the past 450,000 years. As you can see, for 450,000 years, CO2 went up and down. But CO2 levels never rose over 280 parts per million until 1950. But then something different happens and CO2 increases very fast. At the end of 2012, it is 394 parts per million*. Why?
Because of us and our fossil fuels.
Now, let's look at that graph again, but adding the temperatures for that same period of Earth's history.
See caption.
This graph shows how carbon dioxide and temperature have risen and fallen together in Antarctica over the past 400,000 years.
You can see how CO2 levels change with temperature. Look at what it is doing now.
Yipes!

How do we know what Earth was like long ago?

A big part of the answer is ice cores.
In Antarctica, scientists have drilled down two miles below the surface and brought up samples of the ice. These samples are called ice cores. It's like what you get if you plunge a drinking straw into a slushy drink and pull it out with your finger over the end of the straw. What you will have inside the straw is an ice core—although a very slushy one.
The layers in an Arctic ice core are frozen solid. They give clues about every year of Earth's history back to the time the deepest layer was formed. The ice contains bubbles of the air from each year. Scientists analyze the bubbles in each layer to see how much CO2 they contain. Scientists can also learn about the temperatures for each year by measuring relative amounts of different types of oxygen atoms in the water. (Remember, water is H2O: two hydrogen atoms, and one oxygen.)


Other scientists study cores of sediment from the bottom of the ocean or lakes. Or they study tree rings and layers of rocks to give them clues about climate change throughout history. They compare all their findings to see if they agree. If they do, then their findings are accepted as most likely true. If they don't agree, they go back and figure out what is wrong with their methods.
In the case of Earth's climate history, the facts agree from a lot of different kinds of studies.

source. nasa

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