Summers in the arctic produced growth which absorbed carbon dioxide. That’s the way plants grow. With long enough winters, that CO2 became trapped in the permafrost. Now, as the arctic warms and permafrost is melting, trapped CO2 is being released. One billion metric tons are typically absorbed; but now as much as 1.7 billion metric tones are being released. That release is expected to increase as much as 41% in the next century. One of the largest carbon sinks has become an immense carbon source, feeding back into an escalating cycle.