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Projecting changes in climate systems is different from a weather forecasting and is indeed
a much more manageable issue. Based on the foundation of current climate models, there
is considerable confidence that climate models provide credible quantitative estimates of

future climate change. However, to be able to predict changing climate, the results will not
only depend on the interaction among characteristics of the climate, but also on the amount
of greenhouse gasses (GHGs) released into the atmosphere. The amount of GHGs in the
atmosphere is determined by released gases both from human and natural sources and by
their removal through sinks, which mainly include photosynthesis in vegetation. Furthermore, Abu Dhabi, UAE
the climate reacts over long periods to influences upon it; many GHGs remain in the
atmosphere for thousands of years.

Source: IPCC, 2007; UNEP, 2009

Figure 1 Atmospheric concentrations of important long-lived GHGs over the
last 2,000 years.

Increases since about 1750 are attributed to human activities in the industrial era. Concentration
units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules
of the GHG per million or billion air molecules, respectively, in an atmospheric sample.

Concentrations of Greenhous Gases from 0 to 2005
400 2000

1800
Carbon Dioxode (CO )
2 1600
Methane (CH )
CO 2 (ppm), N 2 O (ppb) 300 2 1400 CH 4 (ppb)
4
350
Nitrous (N O)

1200

1000

800

250 600
0 500 1000 1500 2000
Year

IEA Training Manual Workshop for the National Reporting Toolkit (NRT) 13