El Nino inhibits CO2 sequestration

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http://www.bbc.com/news/science-environment-41604760
Nasa carbon space observatory 'watches Earth breathe'
By Jonathan Amos

"If future climate is more like this recent El Niño, the trouble is the Earth may actually lose some of the carbon removal services we get from these tropical forests, and then CO2 will increase even faster in the atmosphere," explained Scott Denning, an OCO science team member from Colorado State University in Fort Collins. That would amplify warming, he told reporters.

But in this extraordinary El Niño period, the jump was 3ppmv, per year - or six gigatonnes.
It is a rate of increase not seen on Earth in at least 2,000 years.

OCO is very accurate in its measurements but it only sees a very narrow swath (10km wide) of the Earth when it flies overhead.
Europe is planning a constellation of satellites called Sentinel-7 that will map CO2 over a much wider area, but still at very high precision.
S7 will trace in much more detail the sources and sinks of carbon dioxide.
This orbiting network would even make it possible to police individual countries' commitments to reduce carbon emissions under international agreements such as the Paris climate accord of 2015.

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The way this is explained makes sense perhaps for dry drought areas created by El Nino but areas where there was more water would increase CO2 uptake. In western US for example, the trees are shedding more leaves this year because of growth from all the water. I might also hypothesis that all the water last winter increased the growth of grasses which now combined with a hot dry summer and fall increases wildfires which releases more CO2.

Another factor is when precipitation falls as rain instead of snow due to warmer temperatures, it means there is less water in the fall. This is because snow didn't stick around to melt more slowly giving a steady input rate of water into the streams and rivers. When ground water runs off faster it leaves vegetation drier in the late summer and fall.

This is where forestry departments are interested in studying forest ecology. Knowing which species and which families among species that are more drought resistant or uptake more CO2 and yet don't catch fire as easily might benefit a fast changing climate. Knowing which of these helps plan their forest management and logging practices.

So this article oversimplified it, but having a high resolution satellite network in the future will help understand all of those factors and more.