365 Days of Climate Awareness 4 - Weather vs Climate

365 Days of Climate Awareness  

4 - Weather vs Climate

Weather is the current state of the atmosphere. This involves quite a few basic physical quantities we can measure, known as direct observations, like temperature, pressure, humidity and wind velocity (both speed and direction), precipitation (rain, snow or otherwise), cloud cover. From these direct measurements we derive features of interest like fronts (masses of air colliding with another mass of markedly different temperature, and where storms tend to form).

Climate is the long-term average of weather, but that description is deceptively simple. First, it requires more definition: what extent in space and time? "Long-term" is arbitrary, though 25 years is a commonly agreed-on time scale. 1,000 years is sometimes used, enough time for an ecosystem to stabilize. And the size could range from a small area measured in square meters, to the entire planet.

Beyond defining climate in time and space, it's important to look at some major influences on it. First is the Sun, which has shown with relatively constant brightness during humanity's brief existence of 100,000 years or so. But over the course of the planet's 4.7 billion years, its intensity has increased by nearly 50%. Solar energy is the prime driver of atmospheric events and over the past few million years it can be treated as a constant.

The earth's motion--orbit and rotation on its axis--are by no means constant, and those will be the subject of another post. The arrangement of continents on the planet surface has major, very long-term (on the scale of millions of years) effects on global circulation and climate.

But the ocean is second only to the sun in its dominant role in determining short- and long-term atmospheric patterns, and for that reason plays a huge role in the climate. Seawater is more than 800 times as dense as air, and has more than 4 times the thermal capacity per unit mass. Therefore, by unit volume, the ocean carries 3200 times as much heat as the wind. Ocean water moves far more slowly than wind, but it carries immensely more heat (as evidenced by the Gulf Stream which warms most of Europe). Understanding the dynamics of the ocean is therefore critical to understanding climate change.

Next up: the major greenhouse gases.

Be well!