Just about every hawkish global warming discussion reported in the press begins with the assertion that increases in carbon dioxide will cause a corresponding increase in warming of the Earth’s ecosystem. Man is impacting climate. The proof – carbon dioxide has been changing relatively rapidly since the industrial revolution.
Climate theory disagrees.
Climate theory predicts that carbon dioxide will have only a small direct impact on climate. The amount of direct warming is not generally in dispute. Carbon dioxide is a small molecule and relatively inefficient as a green house gas.
Climate science as practiced by the IPCC predicts that changes in carbon dioxide will cause other pieces of the climate ecosystem to react in very specific ways. That reaction is predicted to be significant. It is widely believed (the conventional wisdom of today) that increased carbon dioxide will cause increased water vapor which will cause the world to suddenly warm much more rapidly until a new equilibrium temperature is reached.
This positive feedback assumes the climate system is highly sensitive to changes in carbon dioxide. The only confirmation of this assumption is the output of computer models. There is no experimental evidence. It’s difficult to predict how the ecosystem will respond with no spare Earth floating around to experiment on.
Climate scientists use complex computer models to predict climate. The IPCC has high confidence in these models.
I do not share their confidence. Computer models have problems. One can only model the known. Unknowns are a problem for computer models, particularly important unknowns…..like the Sun. The IPCC says they have a Low Level of Scientific Understanding about the Sun in the 2007 Report.
Models begin about 150 years ago which means they all encompass only a period of steadily warming temperatures. The last long cooling cycle (The Little Ice Age) ended about 250 years ago.
The period from 1976 to 1998 was one of relatively rapid warming. When the IPCC assumed a high positive feedback from carbon dioxide in their models the models worked better. Carbon dioxide was going up rapidly and so was temperature. One must cause the other? They could not find any other explanation.
Perhaps they didn’t look for one. Or maybe it was something they didn’t know about….like soot. A study in 2008 predicted that as much as 18% of observed global warming might be due to soot.
The UN’s Intergovernmental Panel on Climate Change (IPCC) has been writing Reports on Climate since 1990. Carbon dioxide has been the culprit in every report.
The latest published report is the Fourth Assessment, nicknamed AR4. The IPCC used climate modeling scenarios to predict climate in the year 2100. All Scenarios (B1, A1T,B2, A1B, A2, A1F1) discussed in the IPCC 2007 Summary Report made assumptions relating to carbon dioxide produced by man. The scenarios are not quantified in any other way. No other possible reasons are discussed. Carbon dioxide is the only variable discussed.
Here is a graph from the 2007 IPCC report that describes the various Scenarios considered:
Those scenarios were then used to generate climate predictions using computer models: Here is the graph presented that showed those predictions:
The bars on the far right indicate the variability of each model at the year 2100. The shading in the graph does not strictly match the bars. I suspect that is so the chart will be easier to read the more likely guesses (oops I mean predictions!). The charts were prepared in 2005. The color stripe in the bar is the best estimate number generated by the IPCC for that scenario. The IPCC Synopses made no predictions about the Scenarios. Which Scenarios were likely? Which were silly? The IPCC preferred not to offer an opinion.
When I look at this data, I don’t see computer models that agree with each other. I see scattered data. Scenario A1F1 could produce a 2 degree C change or a 6 degree C change just 95 years after the chart was prepared. One is a change of about twice the rate of the last 100 years, the other predicts six times the current rate of change. The press frequently uses the biggest numbers when reporting. Text associated with the chart stated that the chart only considered 90% of the model runs. 10% were either higher or lower than this chart shows.
There are so many things to consider when trying to model the climate ecosystem… and so many things we don’t know. I am not surprised the models don’t agree. Climate modeling is a very difficult task.
We are just beginning to understand the oceans and the sun. Cloud formations are still a mystery. Aerosols might be important too. And soot. And air pollution. We have a long way to go.
The IPCC admits to all these shortcomings….and then assumes there is a 90% probability that they are right. If recent press reports can be believed the certainty level has risen to 95% in the new soon to be released AR5 Assessment of climate.
I must respectfully disagree. If computer models could accurately predict ice ages, or at least the Holocene, I’d be more impressed. The Medieval Warming Period and the Little Ice Age are too difficult for the modelers right now. So far at least, temperature has failed to live up to the theory presented. The 21st century has been much cooler than predicted by the IPCC.
Carbon dioxide impacts climate. The notion of the strong positive feedback between carbon dioxide and the rest of the climate ecosystem is an interesting theory….but it’s just that ….a theory. It might be right…but recent data indicates that it is wild high. The world will be warmer than it otherwise would be. But how much warmer…..and from what baseline….that’s a difficult question.
And the IPCC is guessing!