Climate Change Caused by Humans
Misleading: Nature Emits Much More
CO2 Than Humans

Misleading: Nature Emits Much More CO2 Than Humans

The claim: Human emissions are dwarfed by natural emissions so human emissions are not important.

Global Carbon Cycle
Figure 1: Global carbon cycle in the 1990s (IPCC, 2007)

Figure 1 shows the global carbon cycle in the 1990s as documented by the IPCC (2007). Units are in GtC/yr (billion tons of carbon per year) with natural fluxes denoted in black and human fluxes denoted in red. As the diagram shows, the natural emissions (sources) to the atmosphere (black up arrows) are 190.2 GtC/yr while the natural removal (sinks) from the atmosphere is also 190.2 GtC/yr. Big numbers, for sure, but they are in balance and effectively cancel each other out.

According to the The Global Carbon Project (GCP), in the year 2008 human emissions of carbon were 10.2 Gt. Natural sinks removed 5.3 Gt of this carbon. Humans caused a net increase of approximately 5 GtC in 2008. Most of that carbon ends up being CO2. In the past few years humans are adding CO2 at a rate of nearly 2 ppm per year which is equivalent to almost 16 Gt (billion tons) CO2 per year. Therefore, humans caused a net increase of 16 GtCO2! So, yes, natural emissions dwarf human emissions, but because natural emissions are balanced by natural sinks, only the human contribution is responsible for the increasing CO2 in the atmosphere.

Data from the GCP also shows:



Scott A. Mandia
Professor - Physical Sciences
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Last updated: 12/5/09