Climatic Data - Climate Change: Identification and Projections - page 17

excursions between the PCM and the PAG varies by a factor of three,
between the Jones-Mann and Loehle reconstructions. It is not our aim to
decide which is the most representative of the actual evolution of global
temperature.

Alignement

0.8

HadCRUT4
Moberg
Ljungqvist
Loehle
Jones-Mann

0.6

0.4

0.2

0

-0.2

-0.4

1700 1750 1800 1850 1900 1950 2000

Figure 2.4. Linking to HadCRUT4

2.3. Concentration of CO 2 in the atmosphere

C ( t ) is the concentration of CO 2 in the atmosphere, expressed in parts per
million by volume (ppm). The line in Figure 2.5 links three segments:
- With a lack of data from before the year 1000, we can assume that the
concentration is equal to a nominal pre-industrial level C E , of 280 ppm.
- Between 1010 and 1958, concentrations are taken from the air bubbles
trapped in Antarctic ice caps in Lawdome 3 .
- Since 1959, atmospheric concentrations are those measured from the
center at Mauna Loa (Hawaii) 4 .

3 http://cdiac.ornl.gov/ftp/trends/co2/lawdome.smoothed.yr75.
4 ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_annmean_mlo.txt.