News Story - BAS Statement about Channel 4 programme on Global Warming
Date: 20 Mar 2007
Many viewers of the recent Channel 4 programme “The Great Global Warming Swindle” have been left confused as to whether or not humans are affecting the climate system. The programme claimed to demonstrate that climatic change is driven by solar influences and that the recent warming is not related to human greenhouse gas emissions. The programme also accused the science community of falsification of results and of a conspiracy of lying – or a “swindle” - about the cause and significance of climate change.
Here we shall clarify three key points:
- The evidence for an unusual recent global warming is unequivocal, and it is very likely that this is due to human activity
- Recent changes in solar activity bear no resemblance to temperature changes.
- Channel 4 used seriously flawed data on which to base their programme.
We will provide also some factual information about what ice cores tell us about past climate changes.
Human activity and recent climate change
The evidence for human induced global warming is given in the recently published report “Climate Change 2007: The Physical Basis – Summary for Policy Makers” by Working Group I of the Intergovernmental Panel on Climate Change (http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf). The report judges that warming of the climate system is unequivocal, and that this is very likely due to human activities. The report is authoritative as it is based on an extensive and rigorous review of the published results of thousands of scientific investigations carried out worldwide. It is trustworthy since the delegates of 113 nations, including those of climate sceptic nations, have challenged and approved its contents.
Erroneous ‘data’ used by Channel 4
Much of the programme was based around a diagram, shown several times, that purported to be world temperature for the last 120 years. This showed a curve, labelled “NASA”, extending to the year 2003. The curve was produced by NASA nearly twenty years ago. Although it showed data only until 1987, it had been stretched and relabelled to suggest it showed the temperature record to 2003. The resulting distortion excludes the significant warming that has occurred since 1987. Other figures similarly misrepresented the current state of knowledge, especially as regards the influence of the Sun on climate, and the strength of the recent climate warming. This was illustrated an article “The Real Global Warming Swindle” by Steve Connor published in the Independent
A comparison of the distorted and undistorted contemporary data reveal that the plot of solar activity bears no resemblance to the temperature curve, especially in the last 20 years. The recent IPCC report indicates that changes in solar irradiance since 1750 account for only ~5% of the increase in radiative forcing of the Earth’s climate compared with the effects of greenhouse gases (such as carbon dioxide, methane and nitrous oxide).
An article by George Monbiot, published in the Guardian, provides useful additional insight into the manner in which the programme misrepresented the facts
Any scientist found to have falsified data in the manner of the Channel 4 programme would be guilty of serious professional misconduct. In contrast, the editorial standards at Channel 4 apparently tolerate the manipulation and misrepresentation of evidence in order to support sensational but unfounded allegations. This might not be a matter for general concern were it not that the issue of climate change is so serious, and the doubt and confusion generated by the programme potentially so damaging.
Ice cores and past climate change
The programme stated that in the past, temperature increases have preceded CO2 increases and that this falsified the link between CO2 and climate change. This refers to the records of Antarctic climate and CO2 obtained from Antarctic ice cores covering the last 650,000 years (See Figure 1). In these, the Earth can be seen to undergo natural changes from glacial conditions to warmer times like the present. When temperature is warm, the CO2 concentration is high, and when temperature is cold, the CO2 concentration is low. During the exit from glacial periods (for example the transition from the last cold period, between about 18000 and 11000 years ago), both temperature and CO2 increased slowly and in parallel. Close analysis of the relationship between the two curves shows that, within the uncertainties of matching their timescales, the temperature led by a few centuries. This is expected, since it was changes in the Earth’s orbital parameters (including the shape of its orbit around the Sun, and the tilt of Earth’s axis) that caused the small initial temperature rise. This then raised atmospheric CO2 levels, in part by outgassing from the oceans, causing the temperature to rise further. By amplifying each other’s response, this “positive feedback” can turn a small initial perturbation into a large climate change. There is therefore no surprise that the temperature and CO2 rose in parallel, with the temperature initially in advance. In the current case, the situation is different, because human actions are raising the CO2 level, and we are starting to observe the temperature response.
A second issue was the claim that human emissions of CO2 are small compared to natural emissions from volcanoes. This is untrue: current annual emissions from fossil fuel burning and cement production are estimated to be around 100 times greater than average annual volcanic emissions of CO2. That large volcanoes cannot significantly perturb the CO2 concentration of the atmosphere is apparent from the ice core and atmospheric record of CO2 concentrations, which shows a steady rise during the industrial period, with no unusual changes after large eruptions.
Over the last 650,000 years Antarctic temperature and CO2 concentrations have followed each other closely, with high concentrations in warm periods and low concentrations in cold periods (from papers by EPICA Community Members 2004 and Siegenthaler et al 2005).
CO2 from ice cores (Law Dome, Antarctica, from papers by Etheridge et al 1996 and by MacFarling Meure et al 2006) and from atmospheric measurements (Mauna Loa, Hawaii, courtesy of NOAA CMDL). The arrows indicate the dates of selected major volcanic eruptions (U = unknown 1258, T = Tambora 1815, K = Krakatau 1883, A = Agung 1963, P = Pinatubo 1991).