What is a science based target?
The idea behind science based targets is to use climate science to set greenhouse gas (GHG) emission reduction targets. The assumption behind the science based target is that climate change, if not restrained to below 2oC as described by the Intergovernmental Panel on Climate Change (IPCC), will cause irreparable damage to the world’s systems, so much so that our current way of life will be irreversibly and significantly altered. Therefore organisations should set GHG emission reduction targets such that they are in line with the decarbonisation required to realise this goal  .
The Science Based Target initiative is a collaboration between CDP, World Resources Institute (WRI), World Wide Fund for Nature (WWF) and the United Nations Global Compact (UNGC). 
Why set a science based target?
The corporate sector, as the largest emitter of emissions has a role to play in the global transition towards decarbonisation. Reducing GHG emissions is both good for business and protects the global community. Science based targets can help companies capitalise on new technologies and operational practices. By setting ambitious targets, you can push your company to transform and lead in innovation. Creating science based targets can also help you stay one step ahead of future regulations and policies regarding GHG emissions. It can also strengthen investor confidence and the credibility of your company as you take a leading position on climate change mitigation. Most of all, setting ambitious target as part of science based targets can help improve profitability and competitiveness in the future where resources get more scarce and expensive, especially those dependent on fossil fuels. 
What is the Sectoral Decarbonisation Approach (SDA)?
The SDA is a method designed for companies to help set GHG reduction targets that will allow for the temperature rise trajectory to stay within 2oC of preindustrial levels. This method uses the science based targets approach and the 2oC scenario derived from one of the models from the International Energy Agency’s (IEA) detailed CO2 sector scenarios. 
SDA is different from other methods used to generate GHG emission target because of its subsector level approach and global least-cost technology perspective. This means that SDA uses data from IEA’s scenario to determine the mix of the currently available sector methods that would be able to meet final demand.. Therefore, the SDA would be able to help companies especially those in large, homogenous and energy intensive sectors with realistic, low cost measures. These sectors are primarily: electricity generation; iron and steel; chemicals; aluminum; cement; pulp and paper; road, rail, and air transport; and commercial buildings. 
How does the SDA work?
The SDA breaks down the 2oC carbon budget into the different sectors, taking into account the growth rate of the sector, relative to economic and population growth, in addition to its mitigation potential. This way, companies can derive their emission targets based on their relative contribution to the total sector activity and carbon intensity relative to their sector’s intensity.
In explaining the SDA in greater detail, it is important to know how the intensity pathways are derived. Firstly, the IEA’s models are used to estimate the carbon intensity of the sectors by dividing the total direct emissions from the sector by the total activity of the sector. This gives the sector intensity pathway. Next, an assumption is made of the homogenous sectors: that their carbon intensity would converge with the sector carbon intensity by 2050. This assumption is used in addition to the sector specific indicators (eg. physical activity or value added) to generate the company’s intensity pathway. Finally, to calculate the company’s carbon budget, the intensity pathway at a specific point of time can be multiplied by their projected activity.
Using the freely available Science-Based Target Setting Tool, companies can determine their target trajectory compared to their sector intensity pathway. Whereafter, they can use the SDA method and tools to determine specific scope 1 and/or scope 2 reduction targets. 
The Science Based Targets Tool can be found at: http://sciencebasedtargets.org/tools/
- Science Based Targets (n.d.) Accessed 10 October, 2017. Retrieved from: http://sciencebasedtargets.org/
- Science Based Tarfets (n.d.) Accessed 19 October, 2017. Retrieved from: http://sciencebasedtargets.org/faq/
- CDP (2015). Sectoral Decarbonisation Approach (SDA): A Method for setting corporate emission reduction targets in line with climate science. Accessed 25 October, 2017. Retrieved from: https://sciencebasedtargets.org/wp-content/uploads/2015/05/Sectoral-Decarbonization-Approach-Report.pdf