Ugly climate models: the intergovernmental panel on climate change can't explain the last 15 years.

• Author: Bailey, Ronald
• Position: Columns - Column

In September the United Nations Intergovernmental Panel on Climate Change (IPCC) released the final draft of Climate Change 2013: The Physical Sciences Basis. The report's "Summary for Policymakers" flatly states: "Warming of the climate system is unequivocal, and since the 1930s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased."

Pretty much everyone concerned with this issue agrees that those are the facts. But what is causing the planet to warm up? Here is where it gets interesting.

The report's "Summary for Policymakers" declares it "extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." Whether that is so can be probed by comparing observed temperature trends with the simulations of the U.N.'s computer climate models, which assume that human influences are driving climate change. According to the IPCC researchers, "There is very high confidence that models reproduce the general features of the global and annual mean surface temperature changes over the historical period, including the warming in the second half of the 20th century" (emphasis in original). So far, so good: Both the model's projections and actual temperatures rose during the latter half of the 20th century.

As evidence that the models "reproduce the general features" of actual temperature trends, the new report provides a handy graph comparing projections made in the panel's previous report with three different temperature records. The report says "the trend in globally-averaged surface temperatures falls within the range of the previous IPCC projections."

But is that so? Most temperature records show that since 1998 the models and observed average global temperatures have parted ways. The temperatures in the models continue to rise, while the real climate has refused to warm up much during the last 15 years.

The IPCC report acknowledges that almost all of the "historical simulations do not reproduce the observed recent warming hiatus." Not to worry, it assures us; 15-year pauses just happen, and you can't really expect the models to simulate such random natural fluctuations in the climate. Once this little slow-down passes, the report maintains, "It is more likely than not that internal climate variability in the near-term...