Temperature and CO2 have always correlated closely, for at least 400,000 years. Here’s a graph of that correlation:
Most climate scientists believe the reason is the “greenhouse effect,” that is, heat is retained more by air with higher levels of greenhouse gasses. CO2 can be absorbed both by land (plants, mostly) and oceans (direct air to water transfer). However, though the oceans have absorbed about a quarter of the carbon we put in the air, ”
There is no hope that this process will take place fast enough to help control the build-up of CO2.” says Michael McElroy, Harvard’s Butler professor of environmental science.
There is no doubt that we have increased the CO2 content of the atmosphere. The carbon in Oil and coal deep underground are permanently sequestered. They only enter the atmosphere if we bring them up and burn them. All combustion of carbon-based fuels releases carbon into the atmosphere. This is indisputable. Every carbon atom burned (oxidized) creates a molecule of CO2. (Burning wood also releases CO2, so clearing of forests also contributes.)
Here’s how atmospheric CO2 levels have increased. Note the rapid rise since the beginning of the industrial revolution.
“Today, CO2 levels are higher than at any time in at least the past 650,000 years because of increased fossil fuel burning.” Thomas Marchitto, University of Colorado
. Here’s a view of the last 1,000 years:
Here’s a chart of the rising CO2 since 1958:
How do we know we’re responsible for that rise, other than the correlation with our use of fossil fuels? That’s explained HERE. 1) Historical records and calculation of carbon released by our burning of fuel.
The roughly 500 billion metric tons of carbon we have produced is enough to have raised the atmospheric concentration of CO2 to nearly 500 ppm. The concentrations have not reached that level because the ocean and the terrestrial biosphere have the capacity to absorb some of the CO2 we produce.* However, it is the fact that we produce CO2 faster than the ocean and biosphere can absorb it that explains the observed increase.
Independent of that analysis, we can tell how much we have contributed by measuring isotopes. Since carbon isotopes decay very slowly(that’s how carbon dating works), we can determine how much CO2 in the atmosphere was from plants (last year’s CO2) and how much from dead dinosaurs (millions of years of decay). All the calculations are available at the LINK.
Here’s the rising methane level, an even more potent greenhouse gas: