I think they are superpositions if two types of graph. First the left hand and bottom graphs. The blue graphs are concentrations of 13C isotope from various sources in the ecosystem. The red graphs are estimates of global temperature in degrees centigrade. Both types of graph are shown as deviations from the long term mean.

So what they show is that as 13C isotope levels drop, global temperatures rise. The drop in 13C concentrations is presumably because carbon from fossil fuels has extremely low isotope content because it mostly decayed, so as the proportion of fossil fuel carbon in the ecosystem rises isotope concentrations fall.

For the right hand graph red and blue are both isotope tracks, one is carbon the other is oxygen, which is being used as a proxy for temperature.