Carbon budget

As awareness on climate change grows and policymakers around the world debate on how to implement decisions that could help the planet, without endangering their country’s economy, the “carbon budget” is becoming a core component to be considered.
A carbon budget represents a global value: it estimates the total cumulative quantity of greenhouse gas that can be emitted over a specified period of time in order to remain within a certain temperature. The budget must be in line with what is scientifically required to keep global warming, and thus climate change, within “tolerable” levels. So how si a carbon budget estimated? Scientists track the relationship between emissions of GHG gases and the increase in global average temperatures. Then, once a safe temperature target is established, the amount of GHG that can still be emitted to respect it can be estimated. A “carbon budget” therefore represents a finite limit to the amount of emissions we can allow ourselves before we are locked into catastrophic climate change. Generally, 2°C is used as the reference point for defining the carbon budget. 
At the 2015 UNFCCC Paris COP, world governments agreed on their intention to limit global temperature rise this century “well below 2°C” with respect to pre-industrial levels and pursue efforts to “limit the temperature increase to 1.5°C”. Specifying the level of ‘pre-industrial emissions’ aims to provide a baseline from which human activity began to significantly influence greenhouse gas (GHG) concentrations in the atmosphere. Although these are the general guidelines, depending on the variables considered, studies are getting very different results as to the allowable carbon budget. 
A 2009 study commissioned by WWF claimed that, if we divide the total carbon budget, globally we can emit on average 9.5 gigatons (Gt) CO2. This corresponds to less than 20% of our current annual global emissions. Hence, if companies, investors, households and governments do not change their current behaviors, and keep up with the current global 47Gt CO2 , we will completely erode the remaining budget by 2030. 
Since we all live in the same atmosphere, scientists have developed a global measure for carbon budgets; however, such budgets must be then shared among all the countries in the world. Moreover, the way in which countries use the carbon budget is up to them to decide. For example, governments may decide whether it is better to invest in public transportation’s efficiency or in improving roads for private cars. This “partitioning” of the budget is what is causing most troubles, especially for huge economic powers that do not want to “share the pie”. This is why, many scientists are now suggesting that it is more useful for countries to set specific timelines for a transition to net-zero carbon emissions, pledging to be at zero by the year 2050 or 2080. This approach would be more actionable than getting hung up on exactly how much carbon can be emitted in the meantime, and potentially delay climate action in the process.