Climate change models take into account different scenarios based on sets of assumptions about possible alternative futures. Thousands of scientists and other technical experts involved with the Intergovernmental Panel on Climate Change (IPCC) have developed a set of future emission scenarios to assess how changes in economic growth, human population, social trends and technological advancements will affect future global emissions with consequent changes to global temperature and sea level rise.
While the IPCC has developed a set of future emission scenarios, the exact amount of warming that will result from any particular trajectory for future greenhouse gas emissions cannot be projected precisely. This is because it depends on details of processes that reinforce or dampen disturbances to the climate system. Important processes involve clouds, aerosols, water vapour, ocean circulations, ice sheets and sea ice, and natural influences on greenhouse gas levels in the atmosphere.
According to the IPCC:
By 2100 the world will have changed in ways that are difficult to imagine – as difficult as it would have been at the end of the 19th century to imagine the changes of the 100 years since. Each storyline assumes a distinctly different direction for future developments, such that the four storylines differ in increasingly irreversible ways. Together they describe divergent futures that encompass a significant portion of the underlying uncertainties in the main driving forces. They cover a wide range of key “future” characteristics such as demographic change, economic development, and technological change. For this reason, their plausibility or feasibility should not be considered solely on the basis of an extrapolation of current economic, technological, and social trends.
In 2000 the IPCC released a Special Report on Emissions Scenarios (or SRES) that introduced six alternative scenarios of how the future might unfold. Each storyline represents different demographic, social, economic, technological, and environmental developments.
Scenarios used in ACT First data
In the “ACT’s Changing Climate” section we provide regional projections reported by CSIRO and Bureau of Meteorology according to the A1 Storyline which describes a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Major underlying themes are convergence among regions, capacity building, and increased cultural and social interactions, with a substantial reduction in regional differences in per capita income.
In the “Projected Trends” graphs for ACT weather and temperature, we include temperature and rainfall projections according to two storylines:
A1B: a balance of technological emphasis between fossil fuel intensive and non-fossil fuel energy sources; and
A1FI: a fossil fuel intensive emphasis
Revised scenarios used IPCC’s recently released Fifth Assessment Report
Although projections for the ACT reported in ACT First follow scenarios from previous IPCC work, the more recent IPCC report has shifted from assessing SRES scenarios to assessing Representative Concentration Pathway or RCP scenarios. The chart below shows how projected CO2 concentrations in A1B and A1F1 SRES scenarios align to the new RCP6 and ACP8.5 scenarios.
