Human History & Global Impacts

The 200,000 yrs of human history and the recent population explosion  We evolved as homo sapiens 200,000 years ago  Population slowly increased for most of this time (our numbers were in the millions for about 199,800 years)  Humans didn’t reach the 1 Billion mark until 1804

 When your parents were born, there were about 3.5 Billion people on earth  So it took ~ 199,800 years to make 1Billion (1800s) but it only took ~ 160 years to add the next 2.5 Billion more  (1970s = 3.5Bill).

 It’s only taken the past 40 years to add 3.5 Billion more (In 2011 we surpassed the 7 Billion mark)  This means the number of humans on earth are increasing exponentially  Exponential growth means more individuals are added to the population with each generation than were added in the last (2 dogs have 4 puppies, those grow up and each have 8 puppies, those grow up and each have 12 puppies)  Exponential growth occurs in nature only when there is enough food and space

Human Population Growth

More people = more impact

Greenhouse Gases over 2000 years

Temperature Increase over 200 years

Carrying capacity  A carrying capacity of an ecosystem for a particular species is: the maximum population number in which that ecosystem can support indefinitely (forever).  How long can our earth support the human species, whose population is increasing exponentially? Have we reached carrying capacity?

Resource limits  A species reached carrying capacity when it consumes a natural resource at the same rate at which the ecosystem can produce that resource.  Members of a population of a particular species use the same resources for the same things, so as carrying capacity is reached, individuals start competing for these resources  Is there enough fuel? Food? Clean water? Material for shelter? Clean Air? We have reached carrying capacity if we are consuming or using these resources faster than the earth can produce them.

Home work Due Thursday the 21 st  Environmental Science book  Chapter 8 section 1 review questions  Chapter 8 section 2 review questions