Revisions from IEA scenario
According to the IPCC, to stay below 450 ppm, GHG emissions need to drop dramatically by 2050: 50% from current levels worldwide, 75% from current levels in developed countries. This is hard to model, so the assumption is that developed countries drop by 75% and developing countries increase by half of the IEA scenario.
IEA scenario description
This is one of two scenarios presented in the World Energy Outlook 2008 http://www.worldenergyoutlook.org/2008.asp, an annual study prepared by the International Energy Agency (IEA) http://www.iea.org/.
IEA's members are the countries of the Organization for Economic Cooperation and Development (OECD) http://www.oecd.org/, which includes all of the world's industrial economies.
The 450 ppm scenario is designed to limit the average global temperature increase to 2 degrees Celsius, the limit recommended in the Fourth Assessment Report (AR4) http://www.ipcc.ch/ipccreports/ar4-syr.htm of the Intergovernmental Panel on Climate Change (IPCC) http://www.ipcc.ch/.
In the 450 ppm scenario, global greenhouse gas (GHG) emissions peak in 2020 and begin to decline through 2030. By 2030 emissions in the OECD countries decline 40% from 2005 levels, while emissions growth in developing countries through 2030 is limited to 15 to 20% above 2005 levels.
The 450 ppm scenario also envisions aggressive action to reduce deforestation and increase CO2 sequestration through the planting of new trees.
Regional and national cap-and-trade systems play an important role in the 450 ppm scenario. The scenario forecasts a CO2 price of $180 per metric ton in 2030.
The IEA projects that through 2030, the 450 ppm scenario will require more than $9 trillion in investments above the leves forecasted in the baseline scenario, an amount equal to 0.55% of global GDP over the period. This additional investment will be offset by $5.8 trillion in fuel savings through 2030, an amount equal to 0.34% of global GDP.