Still not settled

Over the past three decades energy policy has increasingly become determined by public concern about the impact of anthropogenic carbon dioxide emissions on future climate. The message that has received wide coverage is that increasing atmospheric carbon dioxide will lead to a significant increase in global temperature. The alleged danger is that the climate system might pass a tipping point and there will be irreversible climate change.

The message is not new and has its origins in the evolution of understanding of the climate system over the 19^th and 20^th centuries. 

• In the 1820s the French mathematician Joseph Fourier suggested that a greenhouse effect maintaining relative warmth at the surface was linked to atmospheric absorption of earth-emitted radiation.
• In the 1850s English physicist John Tyndall’s experiments confirmed that water vapour and carbon dioxide present in the atmosphere do indeed absorb earth-emitted radiation.
• In the 1890s the Swedish chemist Svante Arrhenius postulated that the advance and retreat of ice ages had been regulated by changing concentrations of carbon dioxide in the atmosphere as a consequence of variations in volcanic activity;
• In the early 1900s it was suggested, based on Arrhenius hypothesis, that the burning of wood and coal would also increase the atmospheric concentration of carbon dioxide and lead to global warming.
• Geophysical measurements identified the cyclic recurrence of ice age events and these cycles were linked to Earth’s orbital variations, not irregular volcanic activity.
• By the late 1950s measurements and a re-assessment of radiation theory conclusively demonstrated that atmospheric greenhouse gases emit more radiation than they absorb and tend to cool the atmosphere; the explanation for the greenhouse effect is more complicated than Fourier’s simple construct.
• By the early 1970s computer models of the climate system had been developed and experiments to determine the stability of climate identified that an increase in carbon dioxide would lead to global warming, thus re-energising the anthropogenic global warming hypothesis..
• The 1985 UN conference on Carbon Dioxide and Climate held in Villach, Austria issued a Statement that claimed, based on computer model projections, a doubling of atmospheric carbon dioxide concentration over the coming century would raise global temperature by between 2^oC and 5^oC with a most likely value of about 3^oC.
• Subsequent developments in climate modelling, as reported by the UN Intergovernmental Panel on Climate Change (or IPCC), have not appreciably varied the projections.

Reading public pronouncements on the expected impacts of anthropogenic global warming, including those issued by the IPCC, one could readily conclude that climate science is settled. We have been told of the likely global temperature projections and their impacts but are shielded from the expressions of uncertainty that pervade the scientific literature. These uncertainties underpin the projections and are relevant to the reality. Based on the computer projections many governments are taking take actions through energy policies to reduce carbon dioxide emissions; actions that impact directly on industry and lifestyle because fossil fuels are a major source of energy.

A 2005 paper that succinctly alerts to the rudimentary status of understanding of the climate system, titled ‘The Gap between Simulation and Understanding in Climate Modeling’, was published in the Bulletin of the American Meteorological Society by Isaac Held of the US Geophysical Fluid Dynamics Laboratory. Two quotes will suffice:

Due to the great practical value of simulations, and the opportunities provided by the continuing increases in computational power, the importance of understanding is occasionally questioned. What does it mean, after all, to understand a system as complex as the climate, when we cannot fully understand idealized nonlinear systems with only a few degrees of freedom?

and

Despite several major observational campaigns designed to guide us toward appropriate closures for deep, moist convection, little consensus exists as to the best formulations for climate models.

Clouds are an integral component of the climate system in that they directly reflect incoming solar radiation back to space. They also interact with the earth’s radiation fields even more than the greenhouse gases. Errors in specification of clouds and their interactions lead directly to errors in projection of future climate state. Held concludes: 

The health of climate theory/modeling in the coming decades is threatened by a growing gap between high-end simulations and idealized theoretical work. 

The uncertainty of climate projections is underscored when we recognise the relationship between the atmospheric and ocean fluids. The mass of the atmosphere is equivalent to 10 metres of ocean depth; the thermal capacity of the atmosphere is equivalent to about 3.5 metres of the ocean depth. The mixed layer where surface winds stir the ocean surface is only about 250 metres thick. The average depth of the oceans is about 4,000 metres. Clearly the oceans are the thermal and inertial flywheels of the climate system. 

The primacy of the oceans is demonstrated by changing upwelling across the equatorial Pacific Ocean during El Niño and La Niña events. Between these events the average global surface temperature can vary by about 1^oC. Our understanding of changing ocean circulations and their impacts on climate over the decadal to century timeframe is limited because systematic observations of sub-surface ocean circulations only commenced with the deployment of ARGOS buoys in the last decade. 

The global temperature change over the past three decades highlights the divergence between climate model projections and reality. Carbon dioxide has been systematically increasing over this time and climate models have consistently projected rates of temperature rise that should have seen warming over the period of between 0.6^oC and 1.5^oC, with a most likely value near 0.9^oC. The actual temperature rise since 1980 has been about 0.3^oC, or only half the minimum warming projected. 

There are a number of reputable scientists who have independently used real-world data with statistical relationships and methods derived from basic physics to address the question of climate sensitivity. Many of these assessments suggest a sensitivity that is below 1^oC for a doubling of carbon dioxide, much less than the computer model projections.

If we look behind the carefully packaged and promulgated official assessments of the sensitivity of climate to carbon dioxide we find a range of assumptions, assertions and approximations. There are many uncertainties and unknowns about the climate system and its future state. In its 1990 first assessment report the IPCC honestly concluded in the scientific assessment:

• There is a greenhouse effect;
• Adding carbon dioxide will enhance the greenhouse effect;
• However we cannot be confident of the timing, magnitude nor regional impacts of such enhancement.

That statement is as true today as it was in 1990. Recent global temperature trends strongly suggest that the climate sensitivity is far less than the projections from computer models would have us believe, projections on which governments rely in the formulation of energy policy.

The availability and cost of energy are fundamental to the competitiveness of our industries and the lifestyles we enjoy. The Precautionary Principle may have once been justification for government intervention in energy policy but it is now time to reassess those interventions. The divergence between climate projections and reality suggest that the national and regional energy mix should not be constrained by climate considerations. Models that only approximately represent the climate system and for which there remains many knowledge gaps are proving misleading and inadequate as a basis for energy policy. 


William Kininmonth is a consulting climatologist who worked with the Australian Bureau of Meteorology for 38 years in weather forecasting, research and applied studies.  For 12 years, until 1998, he was head of its National Climate Centre.  Between 1998 and 2002, he consulted to the World Meteorological Organization, including coordinating an international review of the 1997-98 El Niño event and preparation of a WMO publication, Climate into the 21st Century (Cambridge).

 He is author of Climate Change: A Natural Hazard (Multi-Science Publishing).