Climate and Weather

David M. Hassenzahl

ENV 206: Introduction to Climate Change

Overview

• Weather and Climate defined

• Determinants of weather and climate

• Please read NASA’s Meteorology - Weather And Climate: A Condensed Primer

Relevant Course Objective

• Define climate and climate change, and explain how climate changes over time

Weather

• The phenomena (temperature, precipitation, humidity, wind) occurring in the atmosphere at a given time

• The atmosphere consists of gases held close to Earth by gravity

Climate

Climate is the typical pattern of weather in a given place over an extended period of time (30 or so years)

• Temperature

• Precipitation

• Humidity

• Wind

Precipitation

• Type– Rain, snow, fog, other

• Amount

• Distribution / Seasonality

Temperature

• Average temperature

• Daily highs and lows

• Seasonal highs and lows

Humidity and Wind

• Humidity– Percent of saturation

• Wind speed matters

Winds

• Uneven heating and cooling lead to winds– Water – Land– Land – Land– North – South– Altitude

• Earth’s rotation drives winds– Coriolis effect (See video library)

Climate and ecology

• Climate, along with geology, determines what sorts of plants, animals, and other life can live in a given place

• Humans have developed methods for controlling local climate – Heating and cooling– Building shelter

Köppen Classification of Climates

• Tropical

• Dry

• Mild mid-latitude

• Cold mid-latitude

• Polar

Examples of Climates: Desert

• Low rainfall (<250 mm / 10 in) per year

• Low humidity

• Often hot

• Mojave (Las Vegas)

• Sahara, Gobi

Source: United States Geological Survey

Examples of Climates:Tropical Rainforest

• 1750 – 2000 mm rain (68 – 78 inches)

• Year-round or monsoon rain

• High temperatures and humidity

Tropical Rain Forest

Source: NASA

Examples of Climates

• Mediterranean

• Tundra

• Taiga

• Steppe

Determinants of Climate

• Insolation

• Geography

• Ocean

• Atmosphere

Insolation

• Aka sunlight• Intensity (solar flux)

– Watts per square meter

• Variability– Solar cycles– Solar flares and sunspots

• Angle of incidence– Earth’s tilt– Varies over time

Source: NASA

Earth Energy Balance

Source: NASA

Geography

• Land masses– Continents– Mountains

• Water bodies– Oceans– Seas and large lakes

• Altitude and latitude

• Albedo (reflectivity)

North Pole Ice

Source: NASA

Ocean

• Ocean currents move hot and cold water around the globe

• Evaporation precipitation

• Cold air warms up over hot water

• Hot, humid air condenses, rains when cooled

Why Europe is Warm

wind direction

Warm water flow

Source: NASA

The AtmosphereSource: NASA

Atmospheric Gases

• Nitrogen – N2 (~78%)

• Oxygen – O2 (~21%)

• Argon – Ar (~1%)

• Water vapor (variable, averages 1%)

• “Trace gases” (parts per million / ppm)

Parts per million

• Parts per million, or ppm

• As a fraction of volume– (Can also measure by mass)

• 1 ppm means one atom out of every 1,000,000 atoms in the atmosphere

Trace Gases Include

• Carbon Dioxide – CO2

– 0.0390 % = 390 ppm

• Methane – CH4

– 1.79 ppm

• Nitrous oxide (N2O)– 320 ppb

• Chlorofluorocarbons– ~1 ppb

• Neon• Helium• Krypton• Hydrogen• Xenon• Ozone• Others

Summary

• Weather is atmospheric conditions

• Climate is typical pattern of weather

• Climate is determined by– Insolation– Geography– Ocean– Atmosphere

• Next: How Climate Changes