On average for a given year, plants and soil take up, or fix, about 30 percent of human emissions. But from one year to the next, that number can be as high as 40 percent or as low as 20 percent. Climate scientists aim to pin down exactly what produces this variability so they can account for it and create the most accurate models for predicting future climate.

But there has been significant debate within the climate modeling community over what exactly causes this so-called interannual variability. One side argues that these changes are mostly driven by atmospheric properties, such as temperature and air humidity near the surface. The other says that soil moisture is far more important.

Source: Soil moisture drives year-to-year change in land carbon uptake