- The Earth was formed about 4,540,000,000 years ago.
- In the beginning, the Earth's atmosphere contained very little oxygen (less than 1% oxygen pressure).
- Early plants started to develop more than 2 billion years ago, probably about 2,700,000,000.
- Through photosynthesis, plants uptake carbon dioxide into the biosphere as organic matter, and release oxygen as a byproduct.
- Through geologic time, oxygen accumulated gradually in the atmosphere, reaching a value of about
21% of atmospheric gases at the present time.
- Through geologic time, surplus organic matter has been sequestered in the lithosphere as fossil organic materials
(coal, petroleum, and natural gas).
- Early animals (the first organisms with external shells) started to develop around 600,000,000 years ago.
- Animals operate in the opposite way than plants: they take up oxygen, burn organic matter (food),
and release carbon dioxide as a byproduct.
- Early humans (Australopithecus anamensis) began to develop about 4,100,000 years ago.
- Cool climatic conditions have prevailed during the past 1,000,000 years.
The species Homo sapiens evolved under these climatic conditions.
- Homo sapiens dates back to more than 400,000 years.
- Estimates for the variety Homo sapiens sapiens, to which all humans belong,
range from 130,000 to 195,000 years old.
- The concentration of carbon dioxide in the atmosphere was as low as 190 ppm during the last Ice Age,
about 21,000 years ago.
- The last Ice Age began to recede about 20,000 years ago.
- The agricultural revolution, where humans converted forests and rangelands into farms, began to
develop about 10,000 years ago.
- The agricultural revolution caused a reduction in standing biomass in the biosphere and
reduced the uptake of carbon dioxide in midlatitudinal regions, indirectly contributing, however so slightly, to global warming.
- The concentration of carbon dioxide in the atmosphere increased gradually from a low of 190 ppm 21,000 year ago,
to about 290 ppm in the year 1900, i.e., at an average rate of 0.00478 ppm per year.
- The industrial revolution, where humans developed machines (artificial animals, since they consume fuels, which are mostly
organic matter), began in England about 240 years ago (1767).
- In October 1999, the world's population
reached 6,000,000,000, which is double that of the year 1959 (the doubling occurred in 40 years).
- The world's population is currently increasing at the rate of about 80,000,000 per year (about 1.2 %).
- The current world population is
6,964,568,359 (September 26, 2011).
- The global fleet of motor vehicles is
estimated at 850,000,000 (2010).
- The global fleet of motor vehicles has been recently growing at the rate of 16,000,000 per year.
- Motor vehicles (cars, trucks, buses,
and scooters) account for 80% of all transport-related energy use.
- The concentration of carbon dioxide in the atmosphere, which was at 290 ppm in the year 1900,
rose to 316 ppm in 1959,
or at an average 0.44 ppm per year.
- Measurements of the concentration of carbon dioxide since 1959 (316 ppm) have revealed an increase to 392 ppm in 2011,
or at an average 1.46 ppm per year.
- The concentration of carbon dioxide has increased an average of
about 1.8 ppm per year over the past two decades.
- The concentration of carbon dioxide increased 2.87 ppm in 1997-98, more than in any other year of record.
The year 1998 was the warmest of record.
The year 2002 was the second warmest (to that date).
The year 2003 was the third warmest (to that date).
The year 2004 was the fourth warmest (to that date).
The year 2005 equaled 1998 as the warmest of record.
The year 2007 equaled 1998 as the second warmest of record.
The ten warmest years have occurred in the twelve-year period 1997-2008.
- About 75% of the annual increase in atmospheric carbon dioxide is due to the burning of fossil fuels.
- The remaining 25% is attributed to anthropogenic changes in land use, which have the effect of reducing
the net uptake of carbon dioxide.
- Anthropogenic changes in land use occur when forests are converted to rangelands, rangelands to
agriculture, and agriculture to urban areas.
- Other patterns of land degradation--deforestation, overgrazing,
overcultivation, urban sprawl, desertification, and salinization--reduce
the net uptake of carbon dioxide, indirectly contributing, however slightly, to global warming.