Basic Physical Principles
Climate concepts that are potentially confusing made less so by comparisons to everyday activities.
Melting of the Arctic sea ice does not raise global sea levels because the ice is already in the ocean water, like how melting of ice cubes submerged in a glass of water does not raise the water level of the glass. Melting of the Greenland or Antarctic ice sheets, however, does raise global sea levels because these ice sheets are above ground on solid land surfaces.
Put an ice cube on a small plate with some water, but not so much water that the ice cube floats: it should be resting on the bottom of the bowl surrounded by water. The water will rise and parts of the plate that were not wet will become wet, similar to what happens to low lying coastal areas when ice grounded on land surfaces melts and spills into the ocean.1
Left: The Greenland ice sheet, with elevation lines. Note how the ice sheet is as high as 2,400 meters (7,875 feet).
The Earth’s surface temperature is about 1.4 degrees Fahrenheit warmer than it was in 1900. Is this enough of a change to make a difference? When your sustained body temperature rises from 98.6 to 100 degrees Fahrenheit, it’s a sign that something in your body’s system is changing. Once the temperature rises another degree to 101, you can certainly feel the difference. Like your body, life on Earth is adapted to exist in a narrow temperature range. Earth’s average surface temperature is 57.2 degrees Fahrenheit, a little bit more than half of your average body temperature, and thus a 1.4 degree rise in temperature is proportionally a greater change.2
- Sub-analogy: Health is more than just measuring temperature. The body, like the Earth, is made up of complex, interconnected systems. Measuring temperature alone cannot identify and diagnose potential problems in the system, but it’s a pretty good indicator that something is changing and further investigation is required.3
Why was the 2009-10 winter so cold in the Eastern United States? Turns out, it was warmer than normal in the Arctic at the same time. The Polar Vortex winds that encircle the Arctic keep the frigid air close to the North Pole. These winds strengthen and weaken periodically, as part of a phenomenon known as the Arctic Oscillation (AO). The AO is like a refrigerator door that opens and closes. When the refrigerator door is “closed,” which is designated as a positive AO phase with strong Polar Vortex winds, the Arctic (refrigerator) stays especially cold while the midlatitudes (the rest of the house) stay warm. When the refrigerator door is “open,” which is designated as a negative AO phase with weak Polar Vortex winds and was the case during the 2009-10 winter, the Arctic (refrigerator) warms up, while the midlatitudes (the rest of the house) are colder than normal due to the spillage of the frigid air.4
Left: Temperature anomalies (oranges and reds indicate warm anomalies; blue shades indicate cool anomalies) during a positive “closed refrigerator door” phase of the Arctic Oscillation. This means strong winds and cold air stays inside the Arctic Circle – or “inside the refrigerator.”
1. Analogy from Paquita Zuidema.
2. Analogy from Rear Admiral David Titley and Richard Sommerville.
3. Analogy from Richard Sommerville.
4. Analogy from Jeff Masters.