Climate Science: Understanding the data about global warming

by Lord Julian Hunt

As John Stuart Mill so lucidly explained (in the Darwin year of 1859), liberty requires that opinions and practices , even those most central to government policies should be thoroughly questioned. There must be discussion to show how knowledge and experience are to be interpreted. Climate change science and policy need questioning in just the same way.

There have been three strands of questioning by sceptical politicians, as well as by some engineers and scientists. The first is that since the earth’s surface has been cooling on average over the past few years, there is no need to worry about global warming. The second, (see The Sunday Times of 6 Dec), is that ‘scientists are struggling to to explain the fact that, against their predictions, temperatures have not risen to new highs over the past ten years’. The third is that since there are doubts about how scientists have interpreted measurements, in order to produce their graphs of the variation of global temperature over the past 100 years, it means that projections about future temperatures are not to be trusted, and therefore no action should be taken to curb global warming.

All these points can be answered by experts engaged in research and in policy aspects of climate change. But there are different emphases in the answers. The Royal Society will publish a consensus statement next week. My own views are influenced by my research in fluid mechanics and meteorology, and my experiences as an administrator, communicator, and politician (I wrote an article in Engineering Sustainability in Sept 2009).

The first question, related to the second, is that atmospheric science from the 19th century studies of Arrhenius onwards has shown, from molecular theory and now satellite measurements, that even a small increase of carbon dioxide, methane and other ‘green house gases’ leads to trapping of out going radiation from the earth’s surface . Prof Harries of Imperial College has explained how recent (2007) measurements of radiation reaching satellite instruments, situated far above the atmosphere, show incontrovertibly that this trapping is occurring ever more effectively. The atmosphere and the surface layers of earth therefore are gradually warming up (by about 0.23 deg per decade).

The reason why the earth’s surface is not exhibiting a steady rise (queried by the Sunday Times) is because, every 10-20 years, currents in the oceans bring huge amounts of cool water to the surface, particularly in the Pacific to the west of South America. This lowers the average temperature at the ocean surface and affects the whole atmosphere. There are other periods when this cool area is covered by warm water (although computer models, aided by better instruments in the ocean and on satellites, can describe many of these features, they cannot yet predict their arrival or duration). This is why, over the present decade and probably subsequent decades, there will be periods when the surface temperatures will be flat. However, the average land temperatures during this period have continued to rise (and not due to local urban effects), as Prof Hansen has pointed out. There should be more publicity of these land based temperatures, such as the display on the UK Hadley Centre web site.

Climate scientists emphasise quite rightly that the average global temperatures for this decade are the highest on record (as stated by the World Meteorological Organisation at COP on 8 December); but this does not necessarily convince sceptics about the need for action on global warming. They say that perhaps this is a natural fluctuation and it will decrease. That is why, in my experience, non-scientist are more convinced about the need for action when they see the steady rise upwards of global land temperatures, which has happened during this decade-though it has levelled out over the past two years.

There are parts of the world where changing local weather patterns cause the temperature rise to greatly exceed the global land average, such as China which has risen by 1 degree Celsius in the past ten years. A comparable rate of rise has been measured, and predicted for the Antarctic peninsular. Even more serious has been the effects of these variations in local weather patterns on rainfall; in Assam India, one of the wettest places in the world, in 2006, there was no rain in many districts, while in the normally dry desert of NW India there were floods unknown for at least 50 years.

As to the third question about doubts in interpretation. These are not unknown in all branches of science and many distinguished scientists have made such errors in the past, often with some bias in their judgement based on certain convictions. This is why scientists in my experience are always very sceptical of other scientists, at least as much as the public is reputed to be. So in all fields there are many duplicated experiments and interpretations. Climate science has developed in the same way. All the data points and interpretations have been checked by other groups and more importantly by other techniques. There used to be several temperature graphs of global mean temperature. It was convenient for policy making to consider a single curve, as plotted in IPCC reports. So if there is any possible doubt about a particular groups interpretation, it seems likely to be very small.

But as the world considers this huge issue, it is vital that everywhere in the world, down to individual communities, should measure and understand their own weather and climate; and of course relating that to national and international trends and predictions. How people and communities deal even locally with disease and their economy, should have a parallel in how they face up to climate. This is one of the themes being promoted by Globe.

Comments and suggestions are very welcome.

Lord Julian Hunt, Member of the House of Lords and former Head of the UK Meteorological Office.

Originally published on the GLOBE International COP15 Blog