CHAPTER 1 WHAT IS CLIMATE The aggregate long term weather or state of the atmosphere of any place is known as its climate For example a description of weather might be It rained yes terday in Phoenix while Phoenix gets only Io inches of rain per year would be a statement about climate Descriptions of climate include such weather elements as temperature precip itation humidity wind cloudiness and snow cover The study of climate is known as cli matology A variety of statistical measures and classification systems have been introduced over the years to help illuminate how climate impacts different regions across the world CLIMATE STATISTICs A location's climate can be described by vari ous statistical measures of the elements of weather and climate Mean or average val ues are usually computed for a fairly long time period such as 30 years These means are often calculated for each month and for the year as a whole Io
WHAT IS CLIMATE Extreme maximum and minimum figures help convey the degree of climate variabil ity Information on the frequency of various events such as the number of days per year with thunderstorms or the number of frosts in a typical winter is also important Temperature is one of the most important climate elements Daily mean temperatures may be computed as the average of the daily maximum and minimum temperatures or as the average of temperatures from all 24 hours These daily means can then be used to compute the mean value for a given month AVERAGE SEA LEVEL TEMPERATURES IN JANUARY BON 40 N 2O IN Over 80 50 to 80 20 to 50 10 to 20 Under 10 60's A COMPTIONS MAP A map of mean global surface temperatures for January shows the values adjusted to indicate what the temperatures would be if all the locations were at sea level To convert from degrees Fahrenheit to degrees Celsius subtract 32 and then divide by 1 8 II
INVESTIGATING THE GLOBAL CLIMATE or for the entire year Normal daily maxi mum and minimum temperatures for a given date or month are also frequently cited The average difference between nighttime low temperatures and afternoon highs may be less than 10 °F 6 °C in cloudy climates or at sea but over 30 °F 17°C in deserts The high est and lowest temperatures ever recorded at a site give an idea of the range of tempera tures one might experience living a lifetime in that location Precipitation data are also very impor tant in describing a location s climate Mean AVERAGE SEA LEVEL TEMPERATURES IN JULY Over 80 50 to 80 20 to 50 EOS 10 to 20 Under 10 A coPTONS MN A map of mean global surface temperatures for July shows the values adjusted to indicate what the temperatures would be if all the loca tions were at sea level To convert from degrees Fahrenheit to degrees Celsius subtract 32 and then divide by 1 8 I2
WHAT IS CLIMATE and extreme monthly amounts are often cited with snow often included as liquid equivalent precipitation Snow cover and evaporation data are also important Mean wind speed and prevailing direction humidity and daily hours of sunshine help complete the climate picture BON AVERAGE ANNUAL PRECIPITATION 40 N 20 2G s Inches Over 80 40 to 80 40s 20 to 40 Bos 10 to 20 Under 10 to s A coNPTONS MAP A map shows the mean global distribution of annual precipitation One inch equals 2 54 cm CLASSIFICATION OF CLIMATES No two locations have precisely the same cli mate but there are many useful schemes for classifying climates The ancient Greeks devised a simple scheme Noting the relationship 13
