climate of an area. These controls, acting in different combinations  and  with  varying  intensities,  act  upon temperature, precipitation, humidity, air pressure, and wind to produce many types of weather and therefore climate. Four    climatic    controls    largely    determine    the climate of every ocean and continental region. These controls   are   latitude,   land   and   water   distribution, topography, and ocean currents. Another factor, which is now significant in determining a region's climate, is man.  Man’s  influence  on  climate  through  pollution, deforestation,   and   irrigation,   is   now   considered   a climatic factor. LATITUDE Perhaps   no   other   climatic   control   has   such   a marked effect on climatic elements as does the latitude, or the position of Earth relative to the Sun. The angle at which rays of sunlight reach Earth and the number of Sun  hours  each  day  depends  upon  the  distance  of  the Sun  from  the  equator.  (See  fig.  6-3.)  Therefore,  the latitude  directly  influences  the  extent  to  which  an  air mass  is  heated.  Latitude  influences  the  sources  and direction of air masses and the weather they bring with them into a region. Comparing  an  equatorial  area  to  a  polar  area  can show the importance of latitude as a climatic control. In the former, the Sun is close to being directly overhead during the day throughout the year. Therefore, there is little  difference  between  mean  temperatures  for  the coldest   and   warmest   months.   In   the   polar   area, however, the Sun never rises far above the horizon; that is,  the  angle  of  the  Sun  to  Earth’s  surface  is  always acute.  The  radiant  energy  received  per  unit  area  is therefore slight, and the warming effects of the Sun are relatively weak. 6-9 6   MONTHS  NIGHT AT N. POLE TANGENT SUN RAY SUN RAY SUN RAY SUN RAY SUN RAY SUN RAY SUN RAY SUN RAY SUN RAY TANGENT TANGENT TANGENT TANGENT TANGENT PERPENDICULAR PERPENDICULAR PERPENDICULAR 12  H S  P N  P ARCTIC  CIRCLE TROPIC  OF   CANCER EQUATOR TROPIC   OF   CAPRICORN ANTARCTIC CIRCLE 12  H 12  H 12  H 12  H 12  H 6  MONTHS DAY AT  N. POLE 6   MONTHS NIGHT  AT  S.  POLE 6   MONTHS DAY  AT  S.  POLE 22   DECEMBER - WINTER  SOLSTICE 21 - JUNE -  SUMMER SOLSTICE 22  SEPTEMBER -  AUTUMN EQUINOX 21 -  SPRING EQUINOX POSITION  OF  PERPENDICULAR AND TANGENT SUN RAYS DETERMINES TROPICS OF CANCER AND CAPRICORN AND ARCTIC AND ANTARCTIC CIRCLES POSITION OF DAYLIGHT CIRCLE  DETER- MINES LENGTH OF DAY AND NIGHT. AG5f 0603 Figure 6-3.—Latitude differences in amount of insolation.