Equilibrium climate sensitivity starts with the scientific calculation of the impact of increased greenhouse gases in the atmosphere. It includes the effect of changes in albedo simply as a multiplication factor of greenhouse gas impacts.
Earth’s Energy Balance
There is a simple formula to show the elements that make up the earth’s energy balance. It does not require complex computer programs and months of calculation to compute them.
Apart from constants, there are three factors in this formula that we have to take into account. These are:
- The light from the sun, which warms the earth. This is measured as Total Solar Irradiance (TSI). The average TSI for the period from 1880 to 2021 was 1361 Watts per square metre (W/M2) at the point of maximum impact and 340.25 W/M2 when averaged over the world’s surface. (It is a sphere, not a flat surface, so the total is divided by 4.)
- The proportion of light from the sun which is reflected from the earth and the atmosphere, without warming the earth. This is a multiplication factor is currently around 0.29, and now can be monitored and measured by satellite. This factor is called “albedo”.
- The rest of the light from the sun heats the earth. Much of this heat is radiated back to space as infrared radiation. This is where greenhouse gases (GHGs) come into play. They reduce the “emissivity” into space of the heat radiated from the earth. This factor is estimated to be about 0.62. Climate scientists have established formulae to account for the changes in emissivity due to the forcing (warming) of the various GHGs.
Climate Sensitivity
Increases in the global average temperature can come from a reduction in emissivity or a reduction in albedo. According to the above formula, a reduction in emissivity of 0.01 and a reduction in albedo of 0.01 have about an equal affect on global average temperature. Therefore, it is not reasonable to treat changes in albedo as just a side effect of changes in emissivity. Yet climate scientists do exactly this. Is albedo 0.29 or 0.30? This a real question.
It is not likely that only the increase of GHGs has caused the current level of warming, which is around 1.3°C. Something else was involved. We know that it was not a change in TSI, since the current level is around the same at the average for 1880 to 2021, and possibly slightly lower. Another element to be considered here is a change in albedo.
Calculating equilibrium climate sensitivity
One only has to consider that over the last 20 years estimates for Equilibrium Climate Sensitivity (based on a doubling of CO2) have been between 1.5°C to 4.5°C, It now settling around 2°C to 2.5°C. Obviously, it is an estimate, not a clear and definable number.
Equilibrium climate sensitivity is a calculated prediction. It is like a cost accountant’s use of an overhead factor to establish the cost of an item. Yet warming from GHGs and from reduction in albedo operate quite differently. It would also be useful to separately consider in detail the actual and projected changes in albedo so that we all know what really needs to be done.
This is not just a theoretical point. It is fundamental. It is not true that global warming is entirely due to GHGs. Sea ice, shelf ice and glaciers have their own dynamics. Black carbon has a significant effect on ice cover: it not only due to higher CO2 and other GHGs.
Albedo and climate sensitivity
Clouds are the major source of the world’s albedo, with snow and ice being the next in importance. Volcanic activity, of a minor and major kind, is a source of sulphur oxides in the atmosphere. These increase the world’s albedo and thus provide a temporary cooling effect on the world, more than offsetting the warmth from the volcanic eruptions. While large scale volcanic eruptions do not happen every year, there are frequent smaller eruptions that keep “replenishing” the background level of sulphuric aerosols in the atmosphere.
We are not responsible for volcanic eruptions, but black carbon is our responsibility. So where is the scientific focus on changes in the earth’s albedo? I wanted to find the history of changes in the satellite measure of the earth’s albedo up to 2022, but failed. Apparently it is not one of the USA’s NOAA bundle of statistics, whereas it has lots of data on greenhouse gases. (It may not be simple to calculate, as Graeme Stephens, et al., has shown.)
Black Carbon
The anthropogenic source of any increase in albedo includes increased sulphuric aerosols from burning coal. This serves to increase albedo, and thus reduces the global average temperature. However, in recent years sulphuric aerosols derived from burning coal have been radically cut, particularly by cutting sulphuric acid emissions in China. It would appear that this has been a significant cause of the recent (up to 2021) rise in global average temperatures.
Offsetting the increases in albedo from sulfuric aerosols have been the soot from coal and the emissions from incomplete combustion of diesel fuel. Both of these lower the reflectiveness of snow and ice, and thus reduce the overall albedo.
These “black carbon” sources also contribute to ice and snow melting more quickly than is required by the increased temperature. This makes changes in albedo in the Arctic and Antarctic particularly important.
Both of these sources of polluting emissions can be reduced, if given appropriate attention. This can happen through the reduction of soot from burning coal and by improving the combustion of diesel fuel. It does not require the abandoning of coal or diesel, but rather by using these fuels more appropriately. Measures to reduce black carbon can be (and are) undertaken by nations and companies of goodwill.
Changes in albedo, particularly in the Arctic and Antarctic regions, should begin to receive the attention they deserve. It is likely that net reductions in albedo in these regions have contributed between one third and one half of all warming to date. One wouldn’t know this from the publicity it receives.
Built-in Effects
There is a long-standing belief that increased global warming is built in, and will be exposed later. Yet, so far, there has been no observable built-in effect. While there is a delay in the impact of the warming of the oceans, Pacific warming seems to find a new equilibrium in a matter of a few years via El Nino and La Nina events. It does not have a measurable long-term impact, at least to date.
It is true that the Atlantic meridional overturning circulation (AMOC) is less effective than before, being reduced by 15%. Any change will have an impact on European weather, but, by itself, it should have no effect on global average temperature.
More worrying is the potential loss of ice shelves in Greenland, Antarctica and the snow cover. This will reduce the albedo of the earth and therefore will result in an increase in global average temperature. However, if the loss of snow and ice from these sources can be stopped, there will be no built-in effect. This should concentrate our minds on the issue of the underlying cause of the net melting of ice, and not just assume that it is due to higher temperatures. One has to compare the annual new snowfall with the annual loss of ice.
Conclusion
More work is required to clearly identify the quantum and reasons for reductions in albedo. Even a small reduction in albedo has an impact on the global average temperature. For example, a reduction in albedo from 29% to 28.8% would result in a calculated temperature rise of 0.2°C.
If black carbon were reduced to zero, it is likely that this would lead to a reduction in global average temperature of at least 0.2°C. It should also lead to a reassessment of the 1.5°C target, pushing it a bit higher.
At the same time, cuts in GHG emissions should be carried out. However, let us make sure that the cuts are measured, appropriate and properly timed. A wide range of cuts that hurt the economies of developed and developing nations should not be held as the only priority.
Also, let us also look after our natural environment and not dig up all of the easily accessible currently favoured minerals in a frantic rush to meet a net zero aim. We should bear in mind that the current push towards the electrification of everything uses immature new technologies for batteries. Other less damaging alternatives are available to us, as I will discuss in later posts. Also, net zero should be reconsidered – it may not be a necessary aim.
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