Geoscience Reference
In-Depth Information
last eight thousand years, the Earth has experienced a remarkably
stable and hot period, with an average temperature of 15°C that should
persist for quite a long time given the stable configuration of its
current orbit's astronomical parameters. However, this equilibrium is
brought into question by the increase in pressures resulting from human
activity. These pressures are visible in numerous studies that agree on
a global warming of the temperature of the Earth's surface. In view of
this situation, an intergovernmental group, the IPCC
1
, has been
created through the initiative of the WMO
2
and UNEP
3
, in order to
regularly carry out an assessment exercise on the climatic conditions
of the Earth's surface. The majority of the results discussed below are
taken from reports from IPCC and the literature that has contributed to
them.
2.2.1.
The report on the findings
The combination of long series of temperature measurements on the
ground, sea and more recently from space, allows us to plot a global
distribution of the changes in surface temperature. Several centers
contribute to this collective effort to validate and analyze the data,
including the
Climate Research Unit
(CRU) with the Hadley Center in
the Met Office (HadCRUT3), the
National Climate Data Center
(NCDC) and the
Goddard Institute for Space Studies
(GISS). These
long series are homogenized to correct instrument errors, changes in
the observation sites, disturbances linked to the extension of urban
heat islands, etc. They are also spatialized, using spatial observations
to compensate for lacunae in
in situ
coverage. The picture that we
draw from these time series is very coherent. The conclusion of the
IPCC AR4
4
[SOL 07] is that the Earth's temperature has increased by
0.76 [±0.19]°C since the pre-industrial era (1850-1899) and that the
speed of this warming has progressively accelerated, the degree of
warming having doubled in the last fifty years in comparison with the
last century. The years 2001-2007 have been particularly hot, with an
1 IPCC: Intergovernmental Panel on Climate Change.
2 WMO: World Meteorological Organization.
3 UNEP: United Nations Environment Programme.
4 AR4: The IPCC fourth assessment report.
