The ‘trillionth tonne’ of carbon is a powerful risk indicator (I previously blogged about it here). As the Oxford University hosted web site trillionthtonne.org shows, we have used up around 567 billion tonne of our one trillion tonne carbon budget:
So that leaves 433 billion tonnes. If we go over the budget, we likely commit the planet to 2 degrees Celsius of warming above pre-industrial revolution levels. That level of warming is viewed as commensurate with dangerous climate change since it will produce a range of impacts extremely negative for mankind. How quickly we will grind through that 433 billion tonnes is the topic of this post.
The U.S. government agency the Carbon Dioxide Information Analysis Center (CDIAC) publishes a time series of emissions from fossil-fuel burning, cement manufacture and gas flaring going back to 1751 here and for land-use change emissions here. This is the benchmark record of human-induced emissions for most academic studies.
The recent estimate for fossil-fuel and cement related emissions for the year 2011 is 9.5 billion tonnes and can be found on the CDIAC site here. Land-use change emissions are updated less frequently but have been running at around 1.0 billion tonnes per annum (also available on the CDIAC site).
For 2012, the Global Carbon Project, a collaboration between various universities and scientific institutions from around the world, estimates that fossil fuel emissions (including those associated with cement production) rose by 2.7% in 2012 to reach 9.7 billion tonnes. Put those two numbers together, and we are placing around 10.7 billions tonnes of carbon into the atmosphere. So if we then divide our remaining 433 billion budget by 10.7 billion tonnes of yearly output, we have 40 years before we likely commit ourselves to a world of dangerous climate change.
That is the good news (sort of) since 40 years is quite a long time. The bad news is that carbon emissions are not static, but are expanding every year. Further, that increase is a product of some very powerful forces that are captured in an identity created by Japanese energy economist Yoichi Kaya. The identity breaks down the rise in global carbon emissions into four major components as can be seen below: