“No Need to Panic About Global Warming” was the title chosen by the page editor of the Wall Street Journal (27 January 2012 and now in The Australian, 1 February 2012) to introduce an elegant article on climate change.
For those of us brought up with Douglas Adams masterpiece The Hitchhiker’s Guide to the Galaxy, there is a strange resonance to the WSJ title. The actual Hitchhiker’s Guide of the story had the words “Don’t Panic” on its cover. The resonance to climate is amplified as a computer called Deep Thought was programmed to find the ultimate answer to the ultimate question of Life, the Universe and Everything. It takes Deep Thought over 7 million years to generate the answer that turns out to be the number 42. But then what was the ultimate question?
For computer modelling of climate change the ultimate answer could be around 4.2 degrees centigrade temperature increase for doubling CO2 in the atmosphere. Yet these computing runs take a matter of days not years. Worse they suffer from chaotic instability and there is an issue of convergence, that is to say two to five runs may have a spread of final values that if the calculations were repeated twenty five times might show convergence and cluster around a particular value. Most models are not run twenty five times because time on large computers is expensive. For the spread of values seen from IPCC summaries one might ask whether the range of values is a reflection of non convergent answers as well as the range of starting assumptions?
The computer models give an answer but have the correct questions been put to the present understanding of the behaviour of the atmosphere?
All the projections of future temperatures, sea levels, rainfall and disasters are the results of computer modelling. The critical questions on which the answer depends can be grouped into four components:
- Do present and past measurements of variables describe the behaviour of the atmosphere and oceans?
This is the primary driver of understanding and important in verifying model calculations. In general the measurements are ‘state-of-the-art’. Proxy data can be problematic. An example is tree ring analysis and the arguments over the Medieval Warm Period with the “hockey stick” chart. Combining point temperature measurements into a global temperature is open to sometimes questionable adjustment.
- Are variations of sources and sinks for green house gases well understood?
The uncertainties in understanding sources and sinks of green house gases are greater than the annual increases in CO2. An example is the tortured explanations of the rise of atmospheric methane in the middle of the twentieth century when a simple explanation of leaky natural gas particularly from the Trans-Siberian pipeline would explain it all.
- Is the coupling of the oceans to the atmosphere understood?
The structured change in annual CO2 increases at the time of the Great Pacific Climate Shift of 1977-78 points to the important role of the oceans in setting CO2 levels in the atmosphere. The recent climate models couple the oceans to the atmosphere. However the consequences of decadel oscillations of ocean surface temperature have largely been ignored since their occurrence and extent is not understood.
- How well is climate sensitivity measured?
Climate sensitivity is how much warming is expected from a given change in CO2. There is general agreement that more CO2 in the atmosphere will increase the temperature at the surface of the earth. A simple doubling of the CO2 will give a temperature increase of less than 10C. The IPCC projections of greater increases from 20C to 4.50C are a consequence of positive feedback that follows the IPCC estimated radiative forcing. But attempts to derive this positive feedback from measurements are not encouraging!
So the answers to these questions reveal substantial uncertainties in the input assumptions of the computer models!
When Deep Thought produced the answer 42, a more massive computer was built to find the ultimate question – this computer was the earth! For climate the earth or at least its oceans and atmosphere mostly likely have the answer. Understanding not computer modelling will answer the questions..
Perhaps Douglas Adams was the Jonathan Swift of our time?