Society is confronted with the effects of climate on wildland fire regimes in ecosystems. We use an ecosystem combustion model (PC2FM) developed with atmospheric variables to predict and simulate fire probability. Precipitation, temperature, and oxygen, three major climate variables that affect the combustion dynamics in ecosystems, are used to address climate forced variance in fire frequency. The use of ecosystem fire metrics in combustion chemistry and physics offers a quantitative method for estimating wildland fire intervals and probability in addition to the well-studied forcing by topography, ignition, and vegetation. Here we apply a combustion process model calibrated with a large empirical fire scar data set. Exothermic reactions and rate laws are used to formulate, map and graph wildland fire dynamics. Past and future maps of fire intervals are presented and discussed. Model results are graphed in a simulated ‘climate space’ that includes temperature and the dual effects of water in ecosystem combustion: 1) the production of carbon bonds (fuel) and 2) the inhibition of collision frequency. These contrasting processes of water in ecosystems define Switch Over Loci (climate sensitive ‘tipping points’) that estimate fire probability classes such as: 1) precipitation insensitive, 2) precipitation unstable, and 3) precipitation sensitive. Most of the area in the Interior West falls into category 2 (precipitation unstable) and 3 (precipitation sensitive) because of low moisture and high temperatures.