Earth Science: Climate and Global Warming

The average land temperature relative to the 1950-1980 average temperature via direct in-situ thermometer measurements.

Similar, via satellite measurements

Mass lost from alpine glaciers. The data after 1970 is better, statistically, and shows an acceleration. Data expressed in percentage of ice mass loss relative to the first data point.

Ice caps are also shrinking. Between 1981 and 2000 the total area of the Arctic ice cap has been reduced by 278-thousand square miles; an area roughly the size of Texas. Reports from NASA and the National Snow and Ice Data Center indicate that the ice cap is thinning in the vertical direction as well.

If the ice is melting, then sea levels must be rising, and this effect is also observed.

The CO2 concentration in part per million since 1958. This curve is called the Keeling (Charles David Keeling, 1928-2005) curve. The small wiggles are seasonal variations caused by plants going dormant in the winter, and thus using no CO2.

The Vostock ice cores have been analyzed for atmospheric CO2 content over the last 1000 years. They show fairly steady CO2 levels until the time of large-scale industrialization. The dashed portion of the curve is the Keeling curve from above.

Going back through the ice ages, as measured from ice cores, it can be seen that the modern CO2 concentration is novel.

Schematic infrared absorption in the earth's atmosphere, showing the relative importance of water vapor vs. CO2. (AQ; Allen 1973)

Infrared transmittance (the previous figure upside down, and put on a linear scale, and with real spectral lines run through a realistic atmosphere) in the earth's atmosphere, tagged by species. The most relevant wavelength region for the greenhouse effect is 5 to 30 nm. Modtran interface (to play with input parameters and see the resultant calculated transmittance). Also see for line lists (result: CO2 and water lines blanket the spectrum).

This figure may be more clear. Incoming solar radiation is mostly reflected or ground-absorbed, then the ground re-radiates in the infrared, mostly in the 10 micron window between water vapor walls. Steady state energy flow requires incoming radiation to be balanced by outgoing radiation.

Greenhouse effect figure with accounting on the energy flow arrows. Credit: Kevin Trenberth

Deforestation, Rondonia district, Brazil. Landsat images show healthy vegetation as red. Images were taken in 1975, 1986, and 1992. From USGS Earthshots page.