weather vs climate graphic Weather and climate are different. Think about it this way: climate is what you expect, weather is what you get. Weather is what you see outside on any particular day. It dictates what you grab out of your closet to wear that day. Climate is the average of that weather. For example, you can expect snow in the Northeast in January or for it to be hot in the South in July. It determines your wardrobe - might you need to own snow boots?

When we talk about climate change we have to make sure we don't confuse it with weather. Just because its the hottest day in July on record in a location or the even the coldest winter, that is not necessarily an indicator of climate change. Climate change is indicated by long-term averages (over 30 years) of daily weather. In most places, weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season. Climate, however, is the average of weather over time and space.

Weather

Instructor's Video

Weather is a function of temperature, precipitation, wind and pressure. Temperature is the first building block of weather. It is impacted by your latitude, whether you are far away from or close to the ocean, your elevation and your geographic position (which side of the mountain range are you on?). Latitudes near the equator (the Tropics) diagram showing imbalance of solar radiation by latitude receive more solar energy than anywhere else on Earth. This is primarily because of the tilt of the Earth's axis ( 23.5°) causing these latitudes to receive very intense solar radiation. The polar regions. consistently receive less intense solar radiation. Weather is all about redistributing this energy from the surplus in the Tropics to the deficit at the Poles, and that redistribution takes place right across Sonoma County creating much of our weather. We live at a latitude where we have neither a surplus or a deficit (38°N.)

If you're from the Bay Area, you know the impact on weather that living near the ocean has. How about San Francisco in June vs. Sacramento in June. All those frozen tourists on the Golden Gate Bridge in shorts in July don't realize that we have a very cold current right off shore making the City's summer temperatures very moderate (ok...cold). Sacramento is inland so it heats up. No cool fog to make their nights cooler. Another example of the impacts of the ocean on temperature can be found in Reykjavik, the capitol of Iceland. Reykjavik is located at 64°N, just below the Arctic Circle, yet it doesn't have a single month that averages below freezing. Compare that to Fairbanks, AK also at 64°N. Six months during the year, Fairbanks average high temperature is below freezing! Reykjavik is located right on the ocean and specifically on an ocean warmed by the North Atlantic Drift, a warm current. Fairbanks is far from the moderating impacts of the ocean and is COLD.

Elevation impacts temperature. As we rise in altitude, the temperature drops about 3.5°F per 1000 feet. Why? As you go up in altitude, there is simply less atmosphere above you. The pressure drops and as a result, so does the temperature. In the US. we have very few cities at high elevation but around the world their are major cities and millions of people living at very high altitudes (eg. La Paz, Bolivia"s capitol - 11,942 ft; Quito, Ecuador's Capitol - 9,350 ft.; Bogota, Columbia's capitol - 8,612; Mexico City, Mexico's capitol - 7,382). Why? Cooler temperatures, defensible against enemies, water availability, less insect-borne disease.

map showing annual precipitation globally The yearly precipitation average over the whole world is about 39 inches. This rainfall is distributed very unevenly. Highest rainfall is around the Equator and in the Tropics, the monsoon areas of SE Asia, the west side of continents in the midlatitudes. The driest places are in the sub-tropics, around the poles, in the center of continents far from the ocean, and on the lee side of mountain ranges - rain shadow effect. In order for precipitation to occur, air must rise and cool. Precipitation occurs, therefore, where air is forced to rise - for example when rising over a mountain; because of heating at the Earth's surface; and when cold and warm air collide.

Wind is cause by differences in atmospheric pressure from place to place which is in turn is driven by the unequal heating of the Earth's Surface. There are prevailing winds that are the dominant winds in locations around the World. In North America, we live in the zone of winds called the Westerlies (they blow from west to east). In the Tropics, the winds are easterly - the NE Trade winds in the northern hemisphere and the SE Trade Winds in the southern hemisphere. There are also regionally important winds that occur periodically, for example in So Cal the Santa Ana winds.

Prevailing winds around the world

map of the monsoons south asia The most important regional winds are the monsoons affecting millions of peoples lives. In large areas of Asia, India, Philippines, Indonesia, west Africa, and northern Australia, all are impacted by monsoonal winds. In the summer, air rises over the hot interiors of continents. Warm moist air rushes in from the coasts bringing all of that year's rain. Often it brings with it massive flooding but the monsoons make growing the region's main crop -rice - possible. In the winter, as the interior of cools off, the winds reverse bringing cool dry conditions to these same regions.

There are major atmospheric disturbances that affect regions all over the world. Perhaps the most impressive are tropical cyclones which we call hurricanes. China, Japan, the Philippines, SE Asia, the South Pacific, NW Australia, East Africa, India, Bangladesh, the southern and eastern coast of the US all have to deal with hurricanes.

Climate

Instructor's Video

Climate impacts everything - soil, vegetation, water resources. The study of climate and weather are courses in and of themselves but lets focus on some important facts about climate.

Dry climates (deserts) cover 30% of our planet. They include the desert SW in the U.S.; the Atacama Desert in Chile; the Patagonian desert in Argentina; the Sahara in No. Africa; the Namibian desert in Namibia; the Kalahari Desert in Botswana, Namibia and So. Africa; the steppes of Central Asia and central Australia
They are the result of persistent high pressure; the rain shadow effect of mountain ranges and/or continentality.
Mediterranean climates have dry summers (unlike most places which get most rainfall during summer), mild winters. You and I live in a Mediterranean climate. They are located on the west side of continents centered at about 35° latitude. There are five areas with this climate: Central California, the Mediterranean Basin, Central Chile, Cape Town South Africa, SW and S Australia.
They are the result of the sub-tropical high which moves over these regions in the summer months blocking precipitation. When it the Sub-Tropical High moves south in the winter, storms can move in.

We will be talking about climate change later in the class but to get started:

Instructor's Video.