Implications: Global

Climate trends

Carbon dioxide emissions from all sources (billion tonnes carbon/year)

Carbon dioxide is emitted above all from the use of fossil fuels. For all four scenarios, it is assumed that stabilization of primary energy use is first reached at the end of the 21st century. Source: IMAGE 2.2 (see technical annex)

Key to charts

Climate change is one of the most pressing and complex global environmental issues to come to the fore in the past 30 years. The absence of effective policies to reduce emissions of carbon dioxide (CO₂) and other greenhouse gases in the Markets First and Security First scenarios, as well as slow transfer of technology under the latter, leads to significant increases in CO₂ emissions over the next 30 years (see chart, right). The effects of the economic troubles in a Security First world push down per capita energy consumption and lead to the slower emission growth seen at the end of this period. The policy actions taken under a Policy First scenario, notably carbon taxes and investments in non-fossil-fuel energy sources, effectively curb growth in global emissions. Actual reductions would start around the year 2030. The dramatic behavioural shifts implied under Sustainability First, in conjunction with significantly improved production and conversion efficiencies, result in a very rapid levelling off of emissions followed by a decline by the middle of the 2020s.

Because of time lags in the climate system, these changes in emission patterns will have a delayed effect on the atmospheric concentrations of CO₂ and even more so on the actual changes in climate. Even by the year 2050, some 20 to 25 years after the start of the decline in emissions in the Policy First and Sustainability First scenarios, the atmospheric concentrations are only beginning to level off in Sustainability First and have yet to do so in Policy First (see chart below). Carbon dioxide trajectories in Markets First and Security First continue to climb rapidly, reflecting the weak policies and lack of behavioural changes in these scenarios.

The rate at which climate is changing is indicated by the rate of change in average global temperature (see chart). The relatively long delay in the response of the climate system shows up in the relatively small differences between the scenarios in their early stages. This figure also reflects the complexity of this issue. There are strong links between climate change and other environmental issues, specifically local and regional air pollution. Reduction in emissions of sulphur dioxide (SO₂), for example, leads to temperature increases which can temporarily more than offset the effects of reducing CO₂ emissions. The higher rates of temperature change in the Policy First and Sustainability First scenarios between now and 2032 reflect the successful implementation of SO₂ reduction policies in these scenarios. In the longer term, however, the dynamics in a world resembling Markets First or Security First imply much faster and greater overall temperature rises, whilst the rate of temperature increase slows down in Sustainability First.

Atmospheric concentrations of carbon dioxide (parts per million by volume) The build-up of greenhouse gases follows trends in emissions but the stock has a long life span once in the atmosphere. Only the Sustainability First scenario is on a trajectory to stabilize at 450 ppm (parts per million) carbon dioxide equivalent. Source: IMAGE 2.2 (see technical annex)

Global temperature change (°C per ten years) Temperature change up to the 2030s can no longer be avoided. In all scenarios its rate far exceeds 0.10°C per ten years - the level above which damage to ecosystems is likely. Source: IMAGE 2.2 (see technical annex)

Delays in the response of the climate system are also apparent in other ways. For instance, by 2032, there is very little difference between the scenarios in terms of sea level rise. The total increase since the beginning of the century is approximately 10 cm, yet this level and rate of rise has serious implications for coastal and low-lying regions throughout the world, implying that adaptation measures are important to consider along with attempts to reduce emissions.