Guest post by Ira Glickstein PhD.
We had joy, we had fun, we had Seasons of the Sun.
But the mountains we climbed were but whimsies of our minds.
That song (apologies to Terry Jacks) could well be the theme for the official climate Team as they hike to the airy peak of Mt. Hansen on the supposed 0.8ºC warming since 1880, only to look out at the bleak prospect, for them, of level ground, and the possibility of some cooling over the coming decades.
This is the third of my Tale of the Global Warming Tiger series where I allocate the supposed 0.8ºC warming since 1880 to: (1) Data Bias, (2) Natural Cycles, the subject of this posting, and (3) AGW, which will be the subject of a subsequent posting. Click Tiger’s Tale and Tail :^) to see my allocation and read the original story.
NATURAL PROCESSES AND CYCLES
This posting is about how natural processes and cycles have dominated the global warming experienced since 1880. The base chart for the above graphic is the NASA GISS Global Land-Ocean Temperature Index that indicates the official climate Team estimate of about 0.8ºC net warming, the majority of which they allocate to human activities. In contrast, according to my annotations, the actual net warming is closer to 0.5ºC (0.8ºC – 0.3ºC Data Bias), and most of that, 0.4ºC, is due to natural cycles and processes over which humans have no control or effect.
The violet curve in the graphic is my estimate of the effect of natural cycles from 1880 to the present. There are many natural processes that affect the surface temperature of the Earth, but nearly all of them gain their energy from the Sun which is why I call them Normal Seasons of the Sun. In the following three sections, they are divided into three groups, according to their time scales and effects.
GRADUAL PROCESSES AND CYCLES LESS IMPORTANT ON HUMAN TIME SCALES
Biological life is thought to have existed on Earth for about 3.5 billion years. Over that enormous time period, natural processes and cycles have affected the evolution of life. Absent those processes, we would not be here, or at least not in our current condition. However, some of these processes and cycles operate ponderously slowly, to the point they are barely noticed on the time scale of an individual human life or even on the time scale of ten lives. Therefore, they are of virtually no concern:
(a) Brightening Sun The Sun is about 4.5 billion years old, and about halfway through what is called the main sequence evolution for a star of its type. It has been getting brighter, but very slowly and nearly imperceptibly. In about 5 billion years, the Sun will become a Red Giant, and life as we know it on Earth will no longer be possible. However, the rate of brightening is so small that we may ignore it.
(b) Milankovitch Cycles. The Earth’s orbit around the Sun is affected by slow, cyclic variations in eccentricity (100,000 years), axial tilt (41,000 years), and precesssion (21,000 years). Changes in the Earth’s orbit do not affect the quantity of average yearly solar radiation, but the distribution between equatorial regions and polar regions is affected. This may be the cause of the approximately 100,000 year cycle of ice age glaciations. However, the contribution of these effects over a period as short as that from 1880 to the present is so small we may ignore it.
(c) Heat from Earth’s Core. About 0.01% of the energy responsible for heating the surface of the Earth is due to energy from the decay of radioactive materials in the Earth’s core. This source has a half life measured in billions of years. This is such a tiny fraction of the Earth’s heat budget that we may ignore it.
PROCESSES AND CYCLES OF IMPORTANCE ON HUMAN TIME SCALES
(d) Normal Seasons of the Sun. The nominal 11-year Solar Cycles, during which Sunspot counts vary from low numbers to a peak and then down again, may be as short as 9 years or as long as 14. Magnetic polarity changes for every pair of cycles, so there is an 18 to 28 year magnetic cycle. Often there are series of three or more cycles, spanning periods of 30 to 150 or more years where solar activity may be very low (below 50 spots per month) and series of similar lengths where activity may be very high (above 100 spots per month).
Low Sunspot series are historically associated with decades of unusually cold climate and vice-versa for high Sunspot series. Total Solar Irradiation (TSI) does not change much during a single Sunspot cycle, but, over a series of high (or low) cycles, it may change enough to result in an increase (or decrease) of 0.1ºC. This TSI effect of Solar Cycles accounts for about a quarter of the of 0.4ºC I have allocated for natural cycles.
(e) Henrick Svensmark’s Global Cosmic Ray (GCR) Theory. GCRs have a positive role in the formation of clouds. Low-lying daytime clouds tend to cool the surface of the Earth. Therefore, all else being equal, the more GCRs, the more clouds, and the cooler the surface of the Earth. Increased solar magnetic activity, which coincides with higher Sunspot numbers, may divert some portion of GCRs from reaching the Earth, thereby reducing cloud formation and thus lessening their cooling effects.
Via this mechanism, a series of high Sunspot cycles may indirectly cause surface temperatures to rise, and a series of low cycles may cause them to fall, which is consistent with the historical record. Svensmark’s theory, if correct, could account for some of the 0.4ºC I have allocated to natural cycles and processes.
(f) Multi-Decadal Ocean Oscillations. There are a number of ocean oscillations, with periods of from less than a decade to multiple decades, that affect sea surface temperatures and therefore have climate impacts worldwide. These include the Pacific Decadal Oscillation (PDO), the El-Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), and others. The ENSO, for example, has a warm phase, called El Niño, Spanish for “the boy”, and a cool phase, called La Niña, “the girl”. The El Niño that started in 1998 caused global warming of 0.1ºC to 0.4ºC for a couple years.
While the net effect of any cycle on temperature anomalies is zero, they have significant effects during their high and low durations. Given the existence of several, somewhat independent ocean oscillations, their high and low times may tend to reinforce or cancel each other out, and that may explain multi-decadal episodes of positive and negative anomalies. There may be some correlation of these cycles with solar activity, which is, of course, the main source of their energy. Thus, ocean cycles could account for some of the 0.4ºC I have allocated to natural cycles and processes.
POSITIVE AND NEGATIVE FEEDBACKS OF IMPORTANCE ON HUMAN TIME SCALES
(g) ATMOSPHERIC GASES (net positive feedback). Long-wave radiation from the Earth extends from about 4 to 25 microns, with maximum energy around 10 microns. See the absorption spectrum for “greenhouse” gases. Note that the absorption spectra for water vapor (H2O) in the range of interest extends from about 5 to 8 microns and from around 12 to 25 microns. Note also that the absorption spectra for other atmospheric gases, such as methane (CH4), carbon dioxide (CO2), nitrous oxide (NO2), and oxygen/ozone (O2/O3), partially overlap H2O such that the atmosphere absorbs (and re-emits) nearly 100% of 4 to 25 micron radiation, except for two nearly transparent windows in the 8 to 9 and 10 to 12 micron regions.
Nearly all the carbon gases in the atmosphere are from natural sources, mostly respiration and digestive gasses of living animals and the decay of dead plants and animals. (The small proportion of carbon gases due to human activity, mainly burning of previously sequestered coal, oil, and natural gas, will be discussed in a future topic here on WUWT. For the purposes of this posting, only natural carbon gases are considered.)
When an atmospheric gas absorbs longwave radiation in its spectrum, that radiative energy is re-emitted in a broader spectrum and in all directions, about half towards the Earth and the other half out towards space.
When atmospheric CO2 absorbs 4 to 5 micron radiation from the Earth, or CH4 absorbs 7 to 8 micron radiation, and that energy is re-emitted, some will fall into the nearly transparent windows and head out to space nearly unimpeded. About half of the remaining energy will be re-emitted back towards the Earth’s surface and will add to warming.
The same is true for H2O, NO2, O2, and O3. Thus, increases in any of these gases will tend to increase warming of the Earth, all else being equal. That means, should the surface of the Earth experience a temperature increase, due to natural solar effects or any other cause, and if that increases emission of carbon gases from equatorial and summer temperate oceans, and reduces absorption of carbon gases by the polar and the winter temperate oceans, that will consititute a positive feedback. The inverse is also true. Should surface temperatures decrease, and if this reduces the amount of CO2, CH4, or H2O gases in the atmosphere, that will reduce the “greenhouse” effect, and tend to further cool the surface. Thus carbon gases and water vapor represent a positive feedback to surface warming.
(h) CLOUDS (net negative feedback). Short-wave radiation from the Sun extends from about 0.2 microns (ultraviolet light) to 2 microns (near infrared light), with maximum energy around 0.5 microns (green light in the visible spectrum). Moderate warming of the surface has a net effect of increasing the extent of cloud cover. Daytime clouds reflect much of the short-wave radiation back out to space, which is a powerful negative feedback. However, both day- and nightime clouds also absorb long-wave radiation from the Earth and re-emit about half of it back down, further warming the surface, a positive feedback. There is disagreement over whether the net effect of clouds is warming or cooling. Most of the official climate Team models assume the net effect is positive, others, including me, assume it nets out as negative.
(i) SURFACE ICE (net positive feedback). Ice, having a high albedo (reflective quality of white or light-colored surfaces), reflects much of the short-wave radiation from the Sun back out to space, which has a cooling effect. Warming of the Earth’s surface may thin and ultimately melt the ice and expose the underlying sea water or land. Water and land are less reflective. Thus, warming that causes melting has a net positive feedback.
(j) THUNDERSTORMS, HURRICANES, ETC. (net negative feedback). These tend to mix the atmosphere and, since the surface is generally warmer than the lower air masses, storms and other disturbances of the atmosphere tend to be a cooling influence. Thunderstorms, in particular, tend to lift warmer air from the surface to higher elevations where the heat energy may more readily radiate out to space.
Thus, if warming of the surface causes more water vapor in the atmosphere, and if this causes more thunderstorms and hurricanes, or makes them more intense, they have a negative feedback effect.
(k) PRECIPITATION (net negative feedback). Water vapor in the atmosphere cools by radiation of its heat energy in all directions, including out to space. The vapor condenses, forming liquid (rain) and solid (snow) water precipitates. Since the radiating tends to take place high in the atmosphere, where the heat energy may more readily radiate out to space, this precipitation constitutes a net cooling effect. Rain and snow tend to be cooler than the surface, and that is also a net cooling effect. Thus, if warming of the surface causes more water vapor in the atmosphere, and if this causes more precipitation, that is a negative feedback effect.
(l) VOLCANIC ERUPTIONS. These spew hot gases, liquids, and solids from the bowels of the Earth onto the surface and into the atmosphere. In the short-term, this tends to heat the surface. However, the aerosols from the volcano, basically sulphur and other mineral compounds, are driven high into the air and tend to remain for years, which tends to reflect Sunlight back into space, which, in the longer-term, tends to cool the surface. The net effect is cooling. For example, the eruption at Mt. Pinatubo in 1991 cooled global temperatures 0.1ºC to 0.3ºC for a few years thereafter.
CONCLUSIONS AND REQUESTS
I believe I have hit on and briefly described all the major natural processes and cycles that affect average global temperatures. However, if readers have additional information or corrections to what I said about any of them, or if there are some I missed, I would appreciate detailed comments to improve my summary.
It seems to me that my estimate of 0.4ºC for Normal Seasons of the Sun is fully justified, but I am open to hearing the opinions of WUWT readers who may think I have over- (or under-) estimated this component of the supposed 0.8ºC rise in global temperatures since 1880.
Quite a few readers were kind enough to comment, either expressing general agreement or offering their own estimates.
Some commenters claim that the actual Data Bias is larger than my estimate of 0.3ºC. Some think Data Bias may be responsible for the entire amount of the supposed 0.8ºC rise in global temperatures since 1880, meaning that net warming over that period is ZERO. I accept that Data Bias may be 50% more (or less) than my estimate, which would put it between 0.15ºC and 0.45ºC, but I doubt it could be as large as 0.8ºC.
Others commenters claim that AGW is ZERO. In other words, they believe that rising CO2 and land use changes due to human activities have no effect on temperatures or climate. They believe the lack of effect is due to the negative feedback from cloud albedo and other natural negative feedback processes. I agree clouds have a net negative feedback (most official models assume a net positive feedback) but I do not believe this cancels out all the effects of CO2 on the Earth’s surface absorption of Solar radiation nor of albedo changes due to land use. I accept that AGW may be 50% less (or more) than my estimate, which would put it between 0.05ºC and 0.2ºC, but I doubt it could be as large as 0.8ºC.
What do you think? I have been keeping a spreadsheet record of WUWT reader’s opinions, which I appreciate and value greatly, along with their screen names, and I plan to report the results later in this series.
This is what you may look forward to:
Some People Claim There’s a Human to Blame – Yes, human actions, mainly burning of fossil fuels and changes in land use, are responsible for some small amount of Global Warming.
Is the Global Warming Tiger a Pussy Cat? – If, as many of us expect, natural processes lead to stabilization of global temperatures over the coming decades, and perhaps a bit of cooling, we will realize the whole Global Warming uproar was like the boy who saw a pussy cat and cried tiger.