Other research has attempted to model potential changes to OMZs as a result of rising global temperatures and human impact. This is challenging due to the many factors that could contribute to changes in OMZs. The factors used for modeling change in OMZs are numerous, and in some cases hard to measure or quantify. Some of the processes being studied are changes in oxygen gas solubility as a result of rising ocean temperatures, as well as changes in the amount of respiration and photosynthesis occurring around OMZs. Many studies have concluded that OMZs are expanding in multiple locations, but fluctuations of modern OMZs are still not fully understood. Existing Earth system models project considerable reductions in oxygen and other physical-chemical variables in the ocean due to climate change, with potential ramifications for ecosystems and humans.