The idea of a carbon budget was first introduced by a group known as the Nobel Laureates Symposium. In 2009 this group of scientists, including 20 Nobel Prize winners, signed a memorandum calling for a carbon budget that set limits on global emissions for 2020 and 2050.
Since the dawn of the industrial revolution we have emitted around 531 billion metric tons of carbon from the burning of fossil fuels, cutting down forests and making cement. A 2013 UN report estimated that we can burn no more than a total of 840 billion tons of carbon to have a 50 percent chance of keeping temperature increases within the upper threshold limit.
"We are not on a path that would lead us to respect that climate target," said professor Thomas Stocker, co-chairman of the group that drafted the UN report.
The "Unburnable Carbon 2013," report with Lord Stern, not only stated that we must radically reduce the amount of carbon we emit into the atmosphere, it also made it clear that our current trajectory will far exceed our carbon budget.
According to a 2015 study by researchers at the University College London's (UCL) Institute for Sustainable Resources, we have a maximum carbon budget of no more than 1,100 gigatons of carbon dioxide by 2050. However, our current trajectory will far exceed that number and augur a 5 degree Celsius temperature rise.
We know that we currently have about three times more fossil fuel reserves than we can safely burn. The UCL study specifically indicates which reserves are unburnable. To keep temperatures below the upper threshold limit we must not extract (and burn) US and Australian coal, Canada's tar sands, Arctic reserves and shale gas.
"These results demonstrate," the study says, "the stark transformation in our understanding of fossil fuel availability is necessary."
It is high time that a science based understanding informs policy decisions. Negotiators who are scheduled to convene at the COP21 climate summit in Paris later this year must focus on a science based agreement.
"This gives a clear scientific basis for a carbon budget and an indication of how much carbon we have already used and how much we have left before we start breaking planetary boundaries," said Samantha Smith, head of the climate and energy program of environmental group WWF. "This has gone from being an interesting piece of modeling to being something that now has solid foundation in the IPCC report."
The UCL study states that 82 percent of all known fossil fuel reserves must be left underground. This is at odds with increasing rates of extraction and ongoing exploration. As the study's co-author Paul Ekins explained to National Geographic, putting hundreds of billions of dollars into fossil fuel exploration and development is "deeply irrational" economic behavior.
The UCL report also puts an end to the ruse of carbon capture as the technnological savior that will allow us to continue our unrestrained use of fossil fuels.
A lot of time has been spent focusing on minor efforts that are little more than window dressing. It is time for us to get real about limiting our carbon emissions and crafting science based energy policies.
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