AIR: What does carbon dioxide "parts per million" mean? And why is it important?

Carbon dioxide is a greenhouse gas. Too much carbon dioxide in the air makes Earth get warmer and warmer. When humans burn fossil fuels, like gasoline and coal, carbon dioxide is produced.

This number tells how many parts of carbon dioxide there are in one million parts of air. So, if carbon dioxide is at 388 parts per million (or ppm), that means in one million pounds of air there are 388 pounds of carbon dioxide.

We need to keep a close watch on this number. Carbon dioxide levels have gone sky-high in the past 100 years. Many scientists think that 350 ppm is a much healthier number and that we should try to reduce our use of fossil fuels to get that number back.

Carbon dioxide levels have shot up since the beginning of the Industrial Age. Many scientists think we need to get the level of carbon dioxide in our atmosphere down to 350 parts per million or less. Ref. http://www.ncdc.noaa.gov/paleo/globalwarming/temperature-change.html.

TEMPERATURE: Why is Earth's global average temperature a big deal?

The global average temperature combines the temperatures of all the hot places, all the cold places, and all the places in between. It is a very important measure of changes going on in Earth's machinery. A rise of just one degree Fahrenheit (°F) on a sunny day where you live has little effect. But over the whole Earth, a rise of 1°F makes a big difference. Just think, normally, water at 32°F is solid ice. But water at 33°F is liquid water.

Even a small rise in Earth's global temperature means melting ice at the North and South Poles. It means rising seas. It means flooding in some places and drought in others. It means that some plants and animals thrive while others die. It can mean big changes for humans too.

And that's why this number is a very big deal.

SEA ICE: What is happening to the ice?

During the winter, the top layer of the ocean near the North Pole freezes solid. Every summer some of this ice melts. But not all of it melts. Some of the ice is so thick it stays frozen all the time, even throughout the summer. However, since 1979, when Earth-observing satellites began watching, the ice remaining at the end of summer has been getting smaller and smaller. At the end of summer 2009, the ice was only two-thirds as large as at the end of the summer of 1979.

The image on the left shows the average ice cover at the end of the summers of 1979 - 1981. The image on the right shows the ice cover at the end of summer in 2007. Ref: http://www.nasa.gov/topics/earth/sea_ice_nsidc.html.

So what? The sea ice is an important part of how ocean currents move heat from the equator to the poles and move the cold water from the poles back to the equator. All life in the ocean depends on this energy circulation. All life on land also depends on life in the oceans.

Sea ice is an important measure of our planet's health.

SEA LEVEL: What if it keeps rising this fast?

Planet Health Report gives the amount of sea level rise in millimeters (mm for short). A millimeter is pretty small. It takes about 25 millimeters to make 1 inch. So 50 mm equals about 2 inches.

As global temperature goes up, sea ice in the Arctic and Greenland melts, and sea level rises. Every inch of sea level rise covers 50-100 inches of beach. If the ice keeps melting, global sea level could rise more than 20 feet. That would put a lot of coastlines under water. Whole islands could disappear!

If the Arctic sea ice and ice covering Greenland were to melt, sea level would rise 20 feet (6 meters)! Credit: Center for Remote Sensing of Ice Sheets,.

Sea level is another important measure of how fast our planet is changing.