When the Intergovernmental Panel on Climate Change recently requested a figure for its annual report, to show global temperature trends over the last 10,000 years, the University of Wisconsin-Madison's Zhengyu Liu knew that was going to be a problem.Data from the real world show that the models are wrong. If the models are wrong, then the models are wrong. There has to be unaccounted for, and possibly unknown, factors at work.
"We have been building models and there are now robust contradictions," says Liu, a professor in the UW-Madison Center for Climatic Research. "Data from observation says global cooling. The physical model says it has to be warming."
The scientists call this problem the Holocene temperature conundrum. It has important implications for understanding climate change and evaluating climate models, as well as for the benchmarks used to create climate models for the future. It does not, the authors emphasize, change the evidence of human impact on global climate beginning in the 20th century.Again, if the models are wrong, they need to be changed until they actually model reality. It is not reality that is wrong.
"The question is, 'Who is right?'" says Liu. "Or, maybe none of us is completely right. It could be partly a data problem, since some of the data in last year's study contradicts itself. It could partly be a model problem because of some missing physical mechanisms."This is the "unknown unknowns" problem which means that the models have been over-simplified to point of being wrong.
The data shows cooling over the last 10,000 years, with rising temperatures in the last 100 years. For human civilization, this is actually good news. Continued cooling would lead to a new ice age. A warming trend, even if due to human activity, can be accomadated. Many places on earth regularly deal with rising seas. Warming temperatures may change growing seasons, but the models are contradictory as to whether this is going to be good thing or not. Same with changing patterns of rainfall.
The three models Liu and colleagues generated took two years to complete. They ran simulations of climate influences that spanned from the intensity of sunlight on Earth to global greenhouse gases, ice sheet cover and meltwater changes. Each shows global warming over the last 10,000 years.
Yet, the bio- and geo-thermometers used last year in a study in the journal Science suggest a period of global cooling beginning about 7,000 years ago and continuing until humans began to leave a mark....Again, if the models disagree with real world data, the models are wrong. The factors included in the model are not complete.
With their current knowledge, Liu and colleagues don't believe any physical forces over the last 10,000 years could have been strong enough to overwhelm the warming indicated by the increase in global greenhouse gases and the melting ice sheet, nor do the physical models in the study show that it's possible.Again, and lastly, if the data from the real world contradict the models, the models are wrong. If the models are wrong, then the models are wrong. There has to be unaccounted for, and possibly unknown, factors at work.
This serious contradiction between reality and the models is the same problem with modelling the last 100 years of climate change. The models contradict reality and the models have to change until they no longer do.