In October 2012 the Meteorological Office’s Hadley Center in England, one of a handful of research centers that maintain global temperature databases, released the HADCRUT4 data set, which shows no net global temperature change since 1997. This is in stark contrast to the clear temperature rise from 1968 to 1998, a change of +0.7 oC in 20 years, for a warming rate of 0.035 oC per year. The HADCRUT4 data can be seen at http://www.metoffice.gov.uk/hadobs/hadcrut4/figures/Figure7.png
The Met Office followed up this disclosure with a projection of future warming trends (issued, strangely enough, during the Christmas holidays, and consequently largely missed by the press). In it they predict what they call a “continuation of global warming” over the next five years, reaching a “temperature anomaly” of 0.55 oC by the year 2017. This phrase means that the temperature increase in 2017 relative to the average base reference temperature for the years 1961-1990 will be 0.55 oC. Somehow they neglected to mention that the actual observed temperature anomaly has hovered around the +0.5 oC level since 1998: in other words, it will not be significantly warmer in 2017 than it is now. From 1997 to 2017, according to the Hadley Center’s best estimates, we will have had 20 years without any global warming.
Last week Jim Hansen, a prominent climate modeler at NASA’s Goddard Institute of Space Studies (GISS) in New York City, concurred with the Hadley Center’s historical data. Dr. Hansen was one of the earliest and most vocal proponents of the idea that human activities, especially burning of fossil fuels, are responsible for global warming. GISS also finds that the “five-year running average” of global temperatures, spanning 14 years of data, has not changed in the past decade. This standstill in warming, which was not predicted by any of the climate models, reminds us of the primacy of data over both enormously complex (but still oversimplified) computer models and faith-based beliefs. It also presents a fresh challenge to climate modelers.
Then, two days ago, Dr. Terje Berntsen, a professor at the University of Oslo’s Department of Geosciences and a senior research fellow at the Center for International Climate and Environmental Research in Oslo, released a reassessment of the warming effects of carbon dioxide. His research, incorporating the data showing the last decade and a half of no net global warming, revealed that the “climate sensitivity” for carbon dioxide is about 1.9 oC per doubling of CO2, far below the numbers often quoted in the media.
“Earth’s mean temperature rose sharply during the 1990s. This may have caused us to overestimate climate sensitivity,” Prof. Berntsen explains. “We were most likely witnessing natural fluctuations in the climate system – changes that can occur over several decades – and which are coming on top of a long-term warming.” Also recall that Prof. Ramanathan’s data suggest that soot has two thirds as large a warming effect as CO2 does, so that 40% of the total warming should actually be attributed to soot. Then the climate sensitivity is only about 1.2 oC per doubling of CO2. Of course, the present temperature plateau was not predicted by our models. Predicting the future effects of soot is hard because controlling soot production is relatively easy compared to controlling carbon dioxide release. Future soot emissions from diesel engines and coal-fired power plants will reflect legal and regulatory rules that do not yet exist, and which therefore defy prediction.
We are reminded of the immortal words of that great philosopher, Yogi Berra: “The trouble with predicting the future is that it is very hard.”