Carbon Math

So I was perusing the IPCC Climate Change 2014 Synthesis Report Summary for Policymakers, and noticed this metric:

“Multi-model results show that limiting total human-induced warming to less than 2°C relative to the period 1861–1880 with a probability of >66%7 would require cumulative CO2 emissions from all anthropogenic sources since 1870 to remain below about 2900 GtCO2 (with a range of 2550 to 3150 GtCO2 depending on non-CO2 drivers). About 1900 GtCO2 had already been emitted by 2011.”

So basically, reading this we have a budget to increase net cumulative GtCO2 emissions by an 1000 GtCO2 to keep temperatures below a 2°C increase. The report also shows that we are currently emitting about 40 GtCO2 per year, which means that at the current rate of emission we will consume the entire budget of allowable increase in ~25 years (5 of which we have likely already consumed since its now 2016!).

So while we can and should continue to focus on ways to greatly reduce the level of anthropogenic greenhouse gas emissions, the direness of this situation is causing me to think perhaps we need to consider if there are ways we can actually remove some of this carbon from the atmosphere.

There has been some press around technological solutions that have been proposed to suck carbon out of the air, but currently it is unclear if any of these technologies are scalable or will prove efficient enough to actually remove more carbon from the atmosphere than the emissions generated from the power consumed in the process .

But there is one carbon sequestration process that we know is simple, easy and efficient. Trees. An average mature tree has about 1 metric ton of carbon in it which is equivalent to about 3.7 metric tons of CO2.

Currently, there are about 3T trees on the planet, which is about half as many as there were 12,000 years ago before the dawn of human agriculture. Incidentally, we are continuing to lose about 10M trees a year due to deforestation. However, it is clear that the planet could easily accommodate a much higher amount of tree biomass than we have currently.

So if we want to offset a 1000 GtCO2 increase, how many more trees do we need? The math says we’d need about 270B additional trees, which isn’t even a 10% increase above our current population of trees. At our current rate of emission of 40 GtCO2/year, this could be offset with an increase 11B trees (about 0.4% increase over the current 3T tree population).

If we were to return to the pre-human population of 6T trees that is equivalent to an additional 11,000 GtCO2 being sequestered into the biomass which is over 5 times the current cumulative GtCO2 emissions associated with human activity quoted in the report.

Obviously this is a super simplified view, but these numbers are huge enough that a small percentage increase in the global tree census could have a measurable impact on carbon in the atmosphere.

So the question I have is are we putting adequate emphasis on reforestation and increasing tree density as a means of delaying the effects of climate change?