MORE ON CLIMATE

WEATHER IS NATURE’S MECHANISM TO BLANCE TEMPORARY DIFFERENCES IN PRESSURE WITHIN OVERALL ATMOSPHERIC CIRCULATION. WHEN THE DIFFERENCES IN PRESSURE (RESULTING FROM UNEVEN HEATING BY THE SUN) GROW TOO GREAT, STORMS DEVELOP, AND THE “PURPOSE” OF STORMS IS TO VENT EXCESS ENERGY AND RETURN A FRESH BALANCE. - From “To Follow the Water” by Dallas Murphy -

DURING THE PAST ONE BILLION YEARS, THE EARTH HAS ALTERNATED BETWEEN WARM PERIODS WHEN THE EARTH WAS COMPLETELY ICE FREE AND COLD PERIODS WHEN ICE SHEETS COVERED MUCH OF THE LAND SURFACE. DURING AN ICE AGE, THERE IS A LARGE TEMPERATURE DIFFERENCE BETWEEN THE POLAR REGIONS AND THE EQUATOR.

THE HEIGHT OF THE LAST ICE AGE WAS ABOUT 20,000 YEARS AGO.

WHAT CAUSES ICE AGES? SCIENTISTS ARE NOT TOTALLY SURE. THEY SUSPECT THE FOLLOWING: 1.SOLAR OUTPUT 2.SHAPE OF EARTH’S ORBIT 3.TILT OF THE EARTH ON ITS AXIS 4.ARRANGEMENT OF THE CONTINENTS 5.OCEAN CIRCULATION 6.COMPOSITION OF THE ATMOSPHERE 7.COMBINATIONS OF THE ABOVE

LET’S TAKE A LOOK AT THE LAST 60 MILLION YEARS. BETWEEN 57 AND 52 MILLION YEARS AGO, THE EARTH WAS RELATIVELY WARM. TROPICAL CLIMATES EXTENDED TO THE CENTRAL U.S. TREES GREW IN THE ARCTIC AND ANTARCTICA. ALLIGATORS LIVED ON ELLSEMERE ISLAND (78 DEGREES NORTH). THIS WARM PERIOD IS CALLED THE EOCENE.

ABOUT 52 MILLION YEARS AGO, THE EARTH STARTED TO COOL. BETWEEN 52 AND 36 MILLION YEARS AGO, ICE SHEETS DEVELOPED OVER EASTERN ANTARCTICA. BETWEEN 20 AND 16 MILLION YEARS AGO, THERE WAS A BRIEF RELIEF FROM THE COLD. AFTER THAT, THINGS STARTED TO COOL DOWN, SO THAT BY 7 MILLION YEARS AGO, GLACIERS COMPLETELY COVERED SOUTHEASTERN GREENLAND.

BETWEEN 5 AND 3 MILLION YEARS AGO, THE EARTH WAS WARMER THAN IT IS NOW. TREES GREW IN GREENLAND, ICELAND AND IN NORTHEN CANADA AS FAR NORTH AS 82 DEGREES. THE THIRD MAJOR COOLING BEGAN AROUND 3 MILLION YEARS AGO AND LASTED UNTIL AROUND 14,000 YEARS AGO.

WE THINK OF CLIMATE CHANGES IN GEOLOGIC TIME AS OCCURING GRADUALLY OVER THOUSANDS OF YEARS. THAT IS NOT ALWAYS THE CASE. CONSIDER THE LAST ICE AGE. IT WAS AT ITS PEAK AROUND 18,000 TO 20,000 YEARS AGO. ICE SHEETS 3 KILOMETERS DEEP COVERED MOST OF NORTH AMERICA SOUTH TO THE GREAT LAKES, MOST OF EUROPE SOUTH TO THE BRITISH ISLES, ARGENTINA, CHILE, NEW ZELAND, AND PARTS OF AUSTRALIA.

IT STARTED TO RETREAT AROUND 16,000 YEARS AGO. BY 12,000 YEARS AGO MORE THAN HALF THE ICE SHEET HAD MELTED. THEN, AT APPROXIMATELY 11,000 YEARS AGO, A COOLING EVENT HAPPENED IN AS LITTLE AS 10 YEARS THAT RESULTED IN A REGLACIATION OF PARTS OF NORTHEN EUROPE. THE EVENT IS CALLED THE YOUNGER DRYAS - NAMED FOR A SMALL TUNDRA FLOWER, Dryas octopetala.

IT IS THOUGHT THAT THE YOUNGER DRYAS EVENT WAS CAUSED BY THE RELEASE OF MELTWATER THAT HAD COLLECTED IN A HUGE LAKE INTO THE ST. LAWRENCE SEAWAY AND INTO THE ATLANTIC. LAKE AGASSIZ COVERED SOME 180,000 SQUARE MILES. THE RELEASE OF FRESH WATER SHUT DOWN THE UPPER PART OF THE GLOBAL CONVEYOR AND DIRECTED THE OCEAN CURRENTS FURTHER SOUTH. IT TOOK ALMOST 700 YEARS TO RETURN TO NORMAL.

THERE ARE SOME FACTORS THAT EFFECT CLIMATE ON A SMALLER SCALE (MICRO CLIMATE EFFECTS). A GOOD EXAMPLE IS A HEAT ISLAND. HEAT ISLANDS ARE LARGE URBAN/SURBURBAN AREAS WHERE THE TEMPERATURES CAN BE AS MUCH AS 1 TO 10 o F HOTTER THAN THE SURROUNDING RURAL AREAS. THIS IS BECAUSE OF ALL THE PAVEMENT AND BUILDINGS.

Increased heat enhances photochemical reactions, which increases the particles in the air and thus contributes to the formation of smog and clouds. London receives approximately 270 fewer hours of sunlight than the surrounding countryside due to clouds and smog. Urban heat islands also increase precipitation in cities and areas downwind of cities.

HEAT ISLANDS CAN BE A PROBLEM DURING HOT SPELLS. SINCE THE TEMPERATURES ARE HIGHER THAT WOULD BE EXPECTED, THIS CAN INCREASE MORTALITY RATES. CITIES ARE TRYING TO REDUCE THE HEAT ISLAND EFFECTS BY: 1.USING MORE REFLECTIVE ROOFING MATERIALS 2.PLANTING TREES 3.PLANTING GREEN ROOFS

1935 dust storm, Texas