How do We Know the Rise in Atmospheric Carbon Dioxide Comes from Us?

by Daniel Bailey
(Michigan, United States)

Global Temperatures and Carbon Dioxide, 1880-2009

Global Temperatures and Carbon Dioxide, 1880-2009

To start with, scientists have a pretty good understanding of what the Earth's climate has been throughout its history, why it has changed over time and what specific factors have caused the climate to change.

In truth, the only factor that fully explains all the changes we can see and measure in temperatures, ocean salinity, atmospheric composition, loss of Arctic sea ice volume, and species habitats & ranges is due to the warming from human-derived fossil fuel, mainly CO2, that we have put back into the carbon cycle.

Negative Natural Flux

We have accurate, reliable data for the growth of atmospheric CO2 and for anthropogenic emissions (for details, see Cawley, 2011).

The fact that the net natural flux is negative clearly shows that natural uptake has exceeded natural emissions every year for the last fifty years at least, and hence has been opposing, rather than causing the observed rise in atmospheric CO2.

More Carbon Dioxide is Entering the Ocean

It is true that the fluxes between the oceans and atmosphere depend on temperature, so all things being equal, one would expect atmospheric CO2 to rise in a warming world.

However, the thing the fake-skeptics normally ignore is that CO2 solubility increases with increasing difference in the partial pressures of CO2 between atmosphere and surface waters.

In the real world, all things are not equal, our emissions have caused a difference in partial pressures, which is increasing the oceanic uptake, which more than compensates for the temperature driven change in fluxes.

Evidence that it is Caused by Mankind

The human-caused (anthropogenic) origin of the measured increase in atmospheric concentrations of CO2 is a cornerstone of predictions of future temperature rises.

As such, it has come under frequent attack by people who challenge the science of global warming. One thing noteworthy about those attacks is that the full range of evidence supporting the anthropogenic nature of the CO2 increase seems to slip from sight. So what is the full range of supporting evidence?

There are ten main lines of evidence to be considered:
  1. The start of the growth in CO2 concentration coincides with the start of the industrial revolution, hence anthropogenic;

  2. Increase in CO2 concentration over the long term almost exactly correlates with cumulative anthropogenic emissions, hence anthropogenic;

  3. Annual CO2 concentration growth is less than Annual CO2 emissions, hence anthropogenic;

  4. Declining C14 ratio indicates the source is very old, hence fossil fuel or volcanic (ie, not oceanic outgassing or a recent biological source);

  5. Declining C13 ratio indicates a biological source, hence not volcanic;

  6. Declining O2 concentration indicate combustion, hence not volcanic;

  7. Partial pressure of CO2 in the ocean is increasing, hence not oceanic outgassing;

  8. Measured CO2 emissions from all (surface and beneath the sea) volcanoes are one-hundredth of anthropogenic CO2 emissions; hence not volcanic;

  9. Known changes in biomass too small by a factor of 10, hence not deforestation;

  10. Known changes of CO2 concentration with temperature are too small by a factor of 10, hence not ocean outgassing.

Incontrovertible Evidence

The current, and ongoing, increase in atmospheric carbon dioxide concentration is due to human industrial activities.

In scientific circles this is the climatological equivalent of the Earth being round - a fact so plainly obvious and supported by such a vast body of scientific evidence that to question its reality is absurd.

It quickly becomes clear that it is the humans who have caused the rise in CO2 levels, by burning fossil fuels in the twentieth century. Every other hypothesis makes a host of predictions that do not pass the test of the evidence.

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