3.

3.1
3.2
3.3

3.1

3.1 What emission scenarios are projected?

Human influences will continue to change atmospheric composition throughout the 21st century.

Several emission scenarios were developed by the IPCC, using various hypotheses for the developments in population, technology, income, regional wealth differences... (see the summary for 6 of them). These scenarios were fed into computer models to make projections of atmospheric concentrations of greenhouse gases and aerosols, and hence of future climate changes (see Figure 5).

3.2

3.2 What climate changes are projected for the 21st century?

Human influences will continue to change atmospheric composition throughout the 21st century.

The average global surface temperature is projected to increase by something between 1.4 and 5.8°C (2.5 to 10°F) over the period 1990 to 2100. This wide range is equally due:
to the level of greenhouse gases emissions supposed by each scenario to the response of the individual computer model used
The projected rate of warming is very likely7 to be the fastest in at least the last 10,000 years. It is very likely7 that nearly all land areas will warm more rapidly than the global average, particularly those at high northern latitudes in the cold season (see map).

The average global surface temperature is projected to increase by something between 1.4 and 5.8°C (2.5 to 10°F) over the period 1990 to 2100. This wide range is equally due:
to the level of greenhouse gases emissions supposed by each scenario to the response of the individual computer model used

3.3

3.3 To what extent is climate change due to human activities?

In light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years (i.e., about half of the warming over the last 120 years) is likely7 to have been due to the increase in greenhouse gas concentrations.

The warming over the past 100 years is very unlikely7 to be due to internal variability alone and is unlikely7 to be entirely natural in origin.