Tuesday, January 7, 2020

Rising Emissions are Exhausting our Carbon Budgets

Greenhouse gas emissions are rising and our carbon budget* is dwindling. Between 2014 and 2016, global carbon emissions remained mostly flat, but emissions began to rise again in 2017. They rose in 2018, and there is good reason to believe they have risen again in 2019. According to the UN's 10th Emissions Gap Report, global emissions are expected to keep climbing putting us on track to push past dangerous upper threshold temperature limits.

A report from the Global Carbon Project, expects that emissions from industrial activities and the burning of fossil fuels will add an estimated 36.8 billion metric tons of carbon dioxide into the atmosphere in 2019. They predict that as of the end of 2019 the total carbon emissions from all human activities, including agriculture and land use, will likely cap off at about 43.1 billion tons.

As reported by Carbon Brief there is a wide degree of variability in estimates of our remaining carbon budget.  Recent studies suggest the remaining carbon budget to limit warming to "well below" 1.5C might have already been exceeded by emissions to-date, or might be as large as 15 more years of emissions at our current rate.

In 2014 the IPCC AR5 Earth System Models (ESM) estimated the remaining carbon budget to be 118 gigatons of CO2 (GtCO2) between 2018 and 2100, if temperatures are to be kept below 1.5C. This amounts to approximately three years of current emissions until the budget is exhausted.The IPCC’s new SR15 raises the budget for a 66 percent of avoiding 1.5C to 420GtCO2 (10 years of current emissions). The budget for a 50/50 chance of exceeding 1.5C is increased to 580GtCO2  (14 years of current emissions). We had 420 GtCO2 left in our carbon budget as of Jan. 1st, 2018. As of the end of 2019 we may have less than 350 GtCO2 left in our carbon budget. Given that we emit about 42 GtCO2 a year the remaining CO2 budget will be entirely gone within less than 8 1/2 years.

According to the IPCC's most optimistic assessments we less than ten years to radically slash emissions. Others including Harvard scientist James Anderson, best known for his work on chlorofluorocarbons, think we have less than half that time. Rising emissions will eventually trigger feedback loops that may prove to be tipping points from which we will not be able to recover.

A study by Prof Jason Lowe and Dr Dan Bernie at the UK’s Met Office Hadley Centre incorporates a wide range of additional feedbacks, some of which enhance and some of which reduce future emissions and resulting warming. They find that including these additional feedbacks results in a "well below" 1.5C carbon budget of between -192GtCO2 and 243GtCO2, with a best estimate of 67GtCO2. 

A U.N. Environment Programme report warned that carbon dioxide emissions must fall by 25 percent over the next decade to keep the global temperatures within 2 degrees Celsius of their preindustrial levels. To reach a more ambitious target of 1.5 C, emissions would need to fall by 55 percent. This means that we have to do better than cutting emissions in half in the next decade if we are to have a 50/50 chance of staying within our carbon budget.

Current atmospheric carbon levels are around 410 parts per million. The safe upper threshold limit is around 450 ppm. WMO says the average global temperatures for 2019 were about 1.1 C above those compared with the preindustrial age. University of Tasmania professor Pete Strutton said that WMO data proving high concentrations of anthropogenic greenhouse gas emissions in the atmosphere shows that drastic cuts in CO2 output will no longer be enough to prevent warming by 3 C.

The fact that we are falling behind on emissions reductions and countries are failing to engage in adequate climate action means that we are rushing headlong to catastrophe.

*A carbon budget refers to how much greenhouse gas we can emit into the atmosphere before we pass the point of warming the Earth beyond 1.5 C or 2 C which is considered the safe upper limit.

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