Tingjun Zhang

Tingjun Zhang

Ph.D. Geophysics
Geophysical Institute, University of Alaska Fairbanks, 1993
Senior Research Scientist, National Snow and Ice Data Center/CIRES

E-mail: tzhang@nsidc.org
Office: RL-2, #220
Phone: 303-492-5236
NSIDC Web site »

Research Interests

  • Permafrost, seasonally frozen ground, snow, and ice
  • Cold regions/cold seasons land surface processes
  • Soil temperature and soil thermal regime
  • heat and mass transfer in porous media
  • numerical modeling of geophysical phenomena in cold regions
  • Satellite remote sensing of the near-surface soil freeze/thaw status

Current Research: Degrading Permafrost Across Eurasian Permafrost Regions

figure 1Cumulative net ecosystem exchange (NEE) over the global permafrost domain with/without permafrost carbon with uncertainty (grey) showing a tipping point during the middle of the 21st century.

figure 2

Permafrost sampling on the North Slope of Alaska during the summer of 2009.

Estimates of the total amount of carbon stored in permafrost range from 950 to 1,672 gigatons (Gt). Although there are large uncertainties in these estimates, permafrost carbon is roughly 1.3 to 2.3 times the total carbon currently in the atmosphere. It has been observed that permafrost is warming and thawing worldwide due to the effect of increased greenhouse gases in the atmosphere. As permafrost degrades, portions of permafrost carbon start to thaw and microbial decay resumes, increasing respiration fluxes to the atmosphere. This will, in turn, increase concentrations of atmospheric greenhouse gases, amplify the rate of climate warming, and further accelerate permafrost degradation, resulting in a positive permafrost carbon feedback (PCF) on climate. However, little is known of PCF. In this study, we use model projections to estimate PCF timing and strength.

By 2200, we predict a 10-percent reduction in permafrost area and a 5- to 50-percent increase in active layer depth. This prediction is on the lower end of potential permafrost degradation in the next two centuries. An irreversible tipping point in Arctic carbon balance signalling the start of PCF could occur during the middle of the 21st century (top figure). The estimated cumulative permafrost flux to the atmosphere by 2200 varies between 101 and 127 Gt C. The 10-percent reduction in permafrost area accounts for 62 percent of this permafrost carbon flux. The PCF tipping point is delayed relative to increases in atmospheric temperature, possibly explaining why observed increases in atmospheric CO2 lag behind temperature after glacial terminations. Qualitative evaluations of various sources of uncertainty indicate the actual PCF tipping point and strength uncertainties are greater than our current estimates. Nevertheless, the PCF is strong enough to warrant inclusion in projections of future climate and in international strategies to reduce fossil fuel emissions.


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