A 2018 IPCC report titled Global warming of 1.5°C has estimated the amount of CO2 the world can emit to stay below 1.5°C global warming over pre-industrial levels. The world had already emitted about 2,200 Gt of CO2 from the dawn of the industrial revolution till 2017. To remain below 1.5°C rise, only 420–570 Gt can be emitted till the end of this century. Together, past emissions and tolerable future emissions of CO2 feed into the carbon budget of the world. Past emissions have consumed over four-fifths of the 1.5 °C budgetary carbon allocations. At the current rate of global emissions, these allocations are set to be exhausted in 12 years. IPCC’s Fifth Assessment Report, 2014 estimates a carbon allocation of 2,900 Gt from pre-industrial times to the end of 21st century to limit warming to 2°C. By 2017, the world had consumed over three-fourths of this allocation.These are carbon budgets rather than greenhouse gas (GHG) budgets and the large range for 1.5°C budgetary allocations partly reflects varying assumptions on how fast non-CO2 GHG emissions can be mitigated. Fossil CO2 emissions accounted for less than 68 per cent of GHG emissions in 2018. Thus, while the carbon budget as a concept is useful for policy making in key sectors such as energy, total GHG emissions and the overall emissions budget is equally critical.
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