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Climate Change: the half-biscuit link
23 April 2015

Climate Change: the half-biscuit link

Our planet is constantly bathed in sunshine as it revolves around the sun, absorbing energy that passes through the top of the atmosphere and returning energy to space by reflection and emission of radiant heat. A balance is struck between the incoming and outgoing energy and, while the details vary by region and season, in general we wobble around an equilibrium which is linked to the mean global surface temperature of about 15°C.

Satellites take detailed measurements of the energy budget at the top of the atmosphere (TOA) so it possible to check the balance. When the data are evaluated the figures show that, on average, there is a small excess of energy entering the planet; in other words the equilibrium has been disturbed and the Earth is adjusting – warming – trying to reach a new equilibrium. The cause: the concentration of greenhouse gases, which mediate the equilibrium, has increased.

The energy excess is quite small – the order of half a watt per square metre (see the accompanying diagram from the IPCC AR5 report, with descriptive text). To put this in context, the human body facing the sun exposes about 1 square metre of skin so if this energy could be fully absorbed by the human metabolism it would amount to about 10kcal energy intake per day, roughly the amount of calories in half a very small plain biscuit. Not much, but as any serious dieter will know, a few extra calories per day can have a significant impact on an otherwise equilibrated body over time [1]. Our planet has had a long time, since the Industrial Revolution, for the effects of this imbalance to become manifest e.g. in rising global temperatures.

Tackling climate change is all about addressing those small numbers. It is a global problem but small changes in individual lifestyles to reduce our carbon footprint will collectively help to tackle climate change.

For more detailed information on climate change and the linkage with greenhouse gas emissions see the IPCC website (

Global mean energy budget under present-day climate conditions. Numbers state magnitudes of the individual energy fluxes in Wm-2, adjusted within their uncertainty ranges to close the energy budgets. Numbers in parentheses attached to the energy fluxes cover the range of values in line with observational constraints. ([2],[3])


[1] An additional 10kcal per day will add roughly 1lb of weight in a year (ref. Hall, K. D., 2008: What is the Required Energy Deficit per unit Weight Loss? Int J Obes (Lond); 32(3): 573–576.)

[2] Taken from: Hartmann, D.L., A.M.G. Klein Tank, M. Rusticucci, L.V. Alexander, S. Brönnimann, Y. Charabi, F.J. Dentener, E.J. Dlugokencky, D.R. Easterling, A. Kaplan, B.J. Soden, P.W. Thorne, M. Wild and P.M. Zhai, 2013: Observations: Atmosphere and Surface. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)].Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[3] Wild, M., D. Folini, C. Schär, N. Loeb, E. G. Dutton, and G. König-Langlo, 2013: The global energy balance from a surface perspective. Clim. Dyn., 40, 3107-3134.


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