Where do scientists believe the missing carbon is going? why are they not sure? (site 2)

Question: Where do scientists believe the missing carbon is going? Why are they not sure? (Site 2)

Scientist estimate that 1-2 billion metric tons of carbon a year are missing from the global carbon budget. Scientist cannot account for the location of 15 to 30 percent of the carbon released into the atmosphere each year. Worldwide humans release an estimated amount of 7 billion tons of carbon. Of that 7 billion 3 billion tons is released into the atmosphere and 2 billion tons is absorbed into the ocean, that leaves you with 2 billion tons of carbon. Scientists assume land vegetation absorbs the rest, but they don’t know exactly where or how much. 

Scientists began to suspect that boreal forests were involved. These forests are located at high latitudes in the northern hemisphere between 43°N and 65°N. They cover between 16 and 20 million square kilometers of land. Scientist took measurements of the carbon dioxide levels at ground level and at the tops of the trees in the boreal forest. They found that while the trees where actively photosynthesizing, the trees took in massive amounts of carbon dioxide and when the photosynthesizing slowed there was a slow release of carbon dioxide back into the atmosphere. They also found that large quantities of carbon dioxide are being stored in the soil beneath the trees. Due to this scientist can estimate that some of the carbon dioxide is being absorbed by the trees and soil in the boreal forest. 

in about winter like late november to january