The huge increase in coal-fired plants in China has masked the impact of global warming in the last decade due to the cooling effect of sulfur emissions. But scientists warn that rapid warming likely will resume when the short-lived sulfur pollution is cleaned up and the full heating effect of long-lived carbon dioxide is felt.
The last decade was the hottest on record, and the 10 warmest years have all occurred since 1998. But within that period, global surface temperatures didn't show a rising trend.
The new study shows that while greenhouse gas emissions continued to rise, their warming effect on the climate was offset by the cooling produced by rising sulfur pollution. This combined with the sun entering a less-intense part of its 11-year cycle and the peaking of the El Niņo climate-warming phenomenon.
The number of coal-fired power stations in China multiplied enormously in that period: the electricity-generating capacity rose from just over 10 gigawatts (GW) in 2002 to >80 GW in 2006.
But rather than suggesting that cutting carbon emissions is less urgent due to the masking effect of the sulfur, Prof Robert Kaufman, at Boston University and who led the study, said: "If anything the paper suggests that reductions in carbon emissions will be more important as China installs scrubbers [on its coal-fired power stations], which reduce sulfur emissions. This, and solar insulation increasing as part of the normal solar cycle, [will mean] temperature is likely to increase faster."
Imperial College London Professor Joanna Haigh, explained, "The researchers are making the important point that the warming due to the CO2 released by Chinese industrialization has been partially masked by cooling due to reflection of solar radiation by sulfur emissions. On longer timescales, with cleaner emissions, the warming effect will be more marked."
