What the science says...
There are many lines of evidence which clearly show that the atmospheric CO2 increase is caused by humans. The clearest of these is simple accounting - humans are emitting CO2 at a rate twice as fast as the atmospheric increase (natural sinks are absorbing the other half). There is no question whatsoever that the CO2 increase is human-caused. This is settled science.
Climate Myth...
CO2 increase is natural, not human-caused
that atmospheric CO2 increase that we observe is a product of temperature increase, and not the other way around, meaning it is a product of natural variation...it may be the Emily Litella moment for climate science and CO2 – “Never mind…” (Anthony Watts)
Simple Accounting
The easiest way to prove that the atmospheric CO2 increase is man-made is through a simple accounting approach (i.e. see Cawley 2011). The equation for the change in atmospheric CO2 (ΔCatm) is
This says that if we ‘emit’ a ton of carbon by, say, triggering a volcano then the atmosphere will gain a ton. If we ‘absorb’ a ton of carbon by growing a tree, then the atmosphere loses a ton. We can expand the equation by counting human emissions (HE) and absorption (HA) and natural emissions (NE) and absorption (NA) separately.
This works because carbon is additive. If a volcano emits a ton of carbon and a factory emits a ton then the atmosphere has gained two tons. This is a very simple balance sheet for the carbon cycle and fortunately there are ‘accountants’ who have measured some of these values for us.
Recently the amount of CO2 in the atmosphere has been rising at ~2 parts per million per year, or around 15 billion tons/year. Meanwhile human emissions excluding land use change (like clearing or planting forests) are 30 billion tons per year. In billions of tons per year we have. Hope this helps! ~ Autumn :)
