The scientific community seems to be confused about the climate change. Zhengyu Liu, a professor at the Center for Climatic Research, University of Wisconsin, says that there are “robust contradictions” between two different studies. That’s why when the Intergovernmental Panel on Climate Change requested data to show global temperature trends over the past 10,000 years, Liu knew there would be contradictions, confusions and problems.

Cooling or warming?

Zhengyu Liu and his colleagues from the U.S. and Chinese universities had been buildings physical models for climate change over the past two years. Findings of the study appeared in the journal Proceedings of the National Academy of Sciences. Data from observation point to cooling. But Liu’s physical models suggest that it has to warming.

Liu and his colleagues describe a global warming trend over the Holocene (about 10,000 years). That contradicts a study published in the journal Science last year, describing a period of global cooling. Scientists have called this issue the “Holocene temperature conundrum.” It will have serious implications for evaluating climate models, and understanding climate change. However, it doesn’t change the impact of human interference on climate change since the inception of 20th century.

Scientists meeting this fall to discuss the climate change conundrum

Now the question is who is right? Liu says perhaps none of them is completely right. The last year’s study might have had some data problems because some data points published in that study contradict itself. Or maybe there is a model problem in Liu’s study due to some missing physical mechanisms. Over the last 10,000 years, the atmospheric carbon emission has gone up by 20 parts per million before the beginning of 20th century. The ice sheet of the Last Glacial Maximum has also retreated. These changes suggest a rise in annual mean global temperatures.

The geo- and bio-thermometers used in the last year’ study indicate that the period of global cooling began about 7,000 years ago and continued until humans began to make a mark, which reflects profound global warming trend. Scientists will meet this fall to discuss the climate change issue. Liu says it’s a puzzle. Both groups should look back critically to find out what’s missing.