Science is about using observation and reason to understand the physical world. Some people are suspicious of computer models and theories; so here is some of the the basic data in pictures and graphs.
Ice core data gives a good picture of what has happened to the Earth in the last several ice ages. Please note that the concentration of CO2, which amplifies the effect of the Milankovitch cycles, did not rise above 300 ppm in the warmer interglacial periods - but now the CO2 concentration is 392 ppm – much higher than any time in the ice core record:
CO2: Man is now putting about 30 billion tons of carbon dioxide into the air each year. About half of it dissolves in the ocean and they have become 20% more acidic in the last century. Much of the rest stays in the air, and CO2 is building up in air:
Temperature: CO2 is one of the greenhouse gases that warm the Earth, and NASA’s graph shows how its increase is changing the Earth’s temperature:
The Sun: The current global warming is often wrongly attributed to an increase in intensity of the sun. The sunspot activity does not show up above the noise in the temperature record above and the solar irradiance increased slightly until 1960 and has declined slightly since then.
Arctic Ice: Many of the changes in the Earth are subtle but here is one of NASA’s pictures which clearly shows how the Earth is changing:
Arctic ice: These two graphs show how both the extent and the volume of the Arctic ice is changing.
Arctic ice volume at each years minimum.
Antarctica: Research by Steig and by O’Donnell show that Antarctica is warming. The warmer oceans result in more snowfall which increases the inland glacier mass, but the erosion of ice by the warmer oceans is causing an overall loss of ice mass.
Antarctic Ice Mass from GRACE satellite data.
Greenland: The Greenland ice sheets are also beginning to decline.
Ocean Level Rise: The melting ice sheets and thermal expansion is causing the oceans to rise by about 3 mm per year which, though it seems small, amounts to an increase in ocean volume of 1190 cubic kilometers/yr.
Rise in Sea Level.
Severe Weather: Warmer temperatures increase both the rate of evaporation and the energy and moisture in the air. This increases the risk of severe weather, droughts, and wildfires. Large insurance companies such as Suisse Re now consider global warming a risk factor as there has been a fivefold increase in billion-dollar weather events in the last 30 years.
Droughts: Below is the Palmer Drought Index which includes most of the continental areas used for food production. Zero represents average rainfall and -4 represents extreme drought. After 1980, drought conditions have grown worse worldwide, and no one disputes the effect of droughts on food production.
Note : This post was updated on 04/03/2012 .
(c) 2012 Que