Hi all. I goofed a bit in my last blog about carbon budgets and made one erroneous comparison. First, thanks to reader James Newberry for catching this.
The problem came when I said the following about the remaining carbon budget globally:
“So to boil this down, if we want a 66% probability, we have about 469 GtC left, which is much less than the 565 GtC McKibben outlined last year.”
The 469 GtC number is accurate based on the latest IPCC report, but by comparing it to Bill McKibben’s 565, I erred. His number was referring to gigatons of carbon dioxide, NOT carbon, which is how the IPCC calculates budget (for the chemically inclined CO2 is 3.67 times as heavy as Carbon alone). Also, Bill’s 565 GtCO2 was the budget until mid-century, 2050. The IPCC numbers are calculated as what we have remaining until the year 2100. Thus I was comparing apples and oranges.
But, I’ve been talking to both Carbon Tracker — the smart guys behind McKibben’s analysis — and my colleagues at PWC UK to check my math. They’ve been recalculating the budgets based on the new IPCC numbers and came to the same conclusion I tried to when comparing 469 to 565 — our budget is getting smaller. So the point is the same, but I used the wrong number to show it.
Anyway, PwC just released in the last couple of days their latest Low Carbon Economy Index. This year, they calculate that we need to decarbonize at a rate of 6% per year until 2100, which is a significant increase from their estimate last year of 5.1% per year. The higher decarbonization rate is due to a reduced underlying budget.
For additional numbers, please see Carbon Tracker’s latest calculations. Their site makes the budget issue as clear as you can.
As you can tell, the numbers can get a bit complicated with you are talking about a variety of scenarios that play with probability of holding our global temperature increase to 2 degrees Celsius, and work with different endpoints in the calendar. But the conclusion is the same. We have to move much, much faster than we are.
