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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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Sun & climate: moving in opposite directions

What the science says...

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The sun's energy has decreased since the 1980s but the Earth keeps warming faster than before.

Climate Myth...

It's the sun

"Over the past few hundred years, there has been a steady increase in the numbers of sunspots, at the time when the Earth has been getting warmer. The data suggests solar activity is influencing the global climate causing the world to get warmer." (BBC)

At a glance

Thankfully for us, our Sun is a very average kind of star. That means it behaves stably over billions of years, steadily consuming its hydrogen fuel in the nuclear reaction that produces sunshine.

Solar stability, along with the Greenhouse Effect, combine to give our planet a habitable range of surface temperatures. In contrast, less stable stars can vary a lot in their radiation output. That lack of stability can prevent life, as we know it, from evolving on any planets that might orbit such stars.

That the Sun is a stable type of star is clearly demonstrated by the amount of Solar energy reaching Earth's average orbital position: it varies very little at all. This quantity, called the Total Solar Irradiance, has been measured for around forty years with high accuracy by sensitive instruments aboard satellites. Its average value is 1,362 watts per square metre. Irradiance fluctuates by about a watt either way, depending on where we are within the 11-year long sunspot cycle. That's a variation of no more than 0.15%.

From the early 1970s until today, the Solar radiation reaching the top of Earth's atmosphere has in fact shown a very slight decline. Through that same period, global temperatures have continued to increase. The two data records, incoming Solar energy and global temperature, have diverged. That means they have gone in opposite directions. If incoming Solar energy has decreased while the Earth continues to warm up, the Sun cannot be the control-knob of that warming.

Attempts to blame the sun for the rise in global temperatures have had to involve taking the data but selecting only the time periods that support such an argument. The remaining parts of the information - showing that divergence - have had to be ditched. Proper science study requires that all the available data be considered, not just a part of it. This particular sin is known as “cherry-picking”.

Please use this form to provide feedback about this new "At a glance" section, which was updated on May 27, 2023 to improve its readability. Read a more technical version below or dig deeper via the tabs above!

Further details

Our Sun is an average-sized main sequence star that is steadily using its hydrogen fuel, situated some 150 million kilometres away from Earth. That distance was first determined (with a small error) by a time consuming and complex set of measurements in the late 1700s. It led to the first systemic considerations of Earth's climate by Joseph Fourier in the 1820s. Fourier's number-crunching led him to realise a planet of Earth's size situated that far from the Sun ought to be significantly colder than it was. He was thereby laying the foundation stone for the line of enquiry that led after a few decades to the discovery of what we now call the Greenhouse Effect – and the way that effect changes in intensity as a response to rising or falling levels of the various greenhouse gases.

TSI Solar cycles

Figure 1: Plot of the observational record (1979-2022) on the scale of the TSIS-1 instrument currently flying on the space station. In this plot, the different records are all cross calibrated to the TSIS-1 absolute scale (e.g., the TSIS1-absolute scale is 0.858 W/m^2 higher than the SORCE absolute scale) so the variability of TSI in this plot is considered to be its “true variability” (within cross calibration uncertainties). Image: Judith Lean.

The Sun has a strong magnetic field, but one that is constantly on the move, to the extent that around every 11 years or so, Solar polarity flips: north becomes south, until another 11 years has passed when it flips back again. These Solar Cycles affect what happens at the surface of the Sun, such as the sunspots caused by those magnetic fields. Each cycle starts at Solar Minimum with very few or no sunspots, then rises mid-cycle towards Solar Maximum, where sunspots are numerous, before falling back towards the end. The total radiation emitted by the Sun – total solar irradiance (TSI) is the technical term – essentially defined as the solar flux at the Earth's orbital radius, fluctuates through this 11-year cycle by up to 0.15% between maximum and minimum.

Such short term and small fluctuations in TSI do not have a strong long term influence on Earth's climate: they are not large enough and as it's a cycle, they essentially cancel one another out. Over the longer term, more sustained changes in TSI over centuries are more important. This is why such information is included, along with other natural and human-driven influences, when running climate models, to ask them, “what if?"

An examination of the past 1150 years found temperatures to have closely matched solar activity for much of that time (Usoskin et al. 2005). But also for much of that time, greenhouse gas concentrations hardly varied at all. This led the study to conclude, " that at least this most recent warming episode must have another source."

TSI vs. T
Figure 2: Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Krivova et al. 2007. TSI from 1979 to 2015 from the World Radiation Center (see their PMOD index page for data updates). Plots of the most recent solar irradiance can be found at the Laboratory for Atmospheric and Space Physics LISIRD site.

The slight decline in Solar activity after 1975 was picked up through a number of independent measurements, so is definitely real. Over the last 45 years of global warming, Solar activity and global temperature have therefore been steadily diverging. In fact, an analysis of solar trends concluded that the sun has actually contributed a slight cooling influence into the mix that has driven global temperature through recent decades (Lockwood, 2008), but the massive increase in carbon-based greenhouse gases is the main forcing agent at present.

Other studies tend to agree. Foster & Rahmstorf (2011) used multiple linear regression to quantify and remove the effects of the El Niño Southern Oscillation (ENSO) and solar and volcanic activity from the surface and lower troposphere temperature data.  They found that from 1979 to 2010, solar activity had a very slight cooling effect of between -0.014 and -0.023°C per decade, depending on the data set. A more recent graphic, from the IPCC AR6, shows these trends to have continued.

AR6 WGI SPM Figure 1 Panel p

Figure 3: Figure SPM.1 (IPCC AR6 WGI SPM) - History of global temperature change and causes of recent warming panel (b). Changes in global surface temperature over the past 170 years (black line) relative to 1850–1900 and annually averaged, compared to Coupled Model Intercomparison Project Phase 6 (CMIP6) climate model simulations (see Box SPM.1) of the temperature response to both human and natural drivers (brown) and to only natural drivers (solar and volcanic activity, green). For the full image and caption please click here or on the image.

Like Foster & Rahmstorf, Lean & Rind (2008) performed a multiple linear regression on the temperature data, and found that while solar activity can account for about 11% of the global warming from 1889 to 2006, it can only account for 1.6% of the warming from 1955 to 2005, and had a slight cooling effect (-0.004°C per decade) from 1979 to 2005.

Finally, physics does not support the claim that changes in TSI drive current climate change. If that claim had any credence, we would not expect to see the current situation, in which Earth's lower atmosphere is warming strongly whereas the upper atmosphere is cooling. That is exactly the pattern predicted by physics, in our situation where we have overloaded Earth's atmosphere with greenhouse gases. If warming was solely down to the Sun, we would expect the opposite pattern. In fact, the only way to propagate this myth nowadays involves cherry-picking everything prior to 1975 and completely disregarding all the more recent data. That's simply not science.

Longer-term variations in TSI received by Earth

It's also important to mention variations in TSI driven not by Solar energy output but by variations in Earth's orbit, that are of course independent of Solar activity. Such variations, however, take place over very long periods, described by the Milankovitch orbital cycles operating over tens of thousands of years. Those cycles determine the distance between Earth and the Sun at perihelion and aphelion and in addition the tilt the planet's axis of rotation: both affect how much heat-radiation the planet receives at the top of its atmosphere through time. But such fluctuations are nothing like the rapid changes we see in the weather, such as the difference between a sunny day and a cloudy one. The long time-factor ensures that.

Another even more obscure approach used to claim, "it's the sun" was (and probably still is in some quarters) to talk about, "indirect effects". To wit, when studies can't find a sufficiently large direct effect, bring even lesser factors to the fore, such as cosmic rays. Fail.

In conclusion, the recent, post 1975 steep rise in global temperatures are not reflected in TSI changes that have in fact exerted a slight cooling influence. Milankovitch cycles that operate over vastly bigger time-scales simply don't work quickly enough to change climate drastically over a few decades. Instead, the enormous rise in greenhouse gas concentrations over the same period is the primary forcing-agent. The physics predicted what is now being observed.

Last updated on 27 May 2023 by John Mason. View Archives

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Expert interview with Mike Lockwood


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Comments 126 to 150 out of 530:

  1. On Venus: When the Galileo satellite passed by, it collected a lot of interesting data. Including the fact that at IR levels, the atmosphere appears strongly absorbing IR. This is attributed to the SO2 clouds. There is further thought that the 'greenhouse' effect on Venus is caused by high level SO2 clouds rather than lower level CO2, and that most of the solar energy absorbed is via SO2. Any water vapour present would have been dissociated by UV and 'blown away' by the solar wind due to the lack of a magnetic field, thus stripping the planat of water. Currently there is a project to carry out a detailed 2 year investigation of Venus' climate and compare its' evolution with our own.
  2. Pep Thanks, that works. Mizimi They have determined that some volcanos also eject high amounts of SO2 on earth. It was mentioned in one of the articles that I linked on the volcanos thread here.
  3. July by Beck on 180 yrs of chemical CO2 analysis...showing previous values of CO2 from 1800'2 have been "beck's 180 year analysis of CO2"....lots of info.
  4. Millions tons of SO2 in the stratosphere, Mt. Pinatubo was a great example. Now it’s overestimated or was. The scare tactic is dying.
  5. Here is the "180_years" PDF.
  6. Pep That was an interesting read, even if it was a draft copy. I found the sections on ENSO and other ocean oscillations particularly of interest. Thank you.
  7. I would take 180 years with a grain of salt. :) welcome
  8. Pep Actually I have not read it yet and I don't know if its the same as what Mizimi read but I will take a look at both links later.
  9. The site contains the full extract; the other is an abstract of the pertinent findings. One possible way to check 'accuracy' is to check out the annual coal tonnages around the 1850-1960 periods as oil did not supplant coal until after this period. I rather suspect (!!)a surprise, especially since coal-burning appliances were notoriously inefficient in those times. Equally much wood was burnt during this period? rather a lot I think, and in very inefficient ways.
  10. Mizimi In rural America, coal and wood still warm many homes, albeit the systems have become somewhat more sophisticated than they were when I was growing up. I would like to use a windmill here but they are quite expensive. I'm waiting for the prices to come down.
  11. R. Keeling has posted a rebuttal and Beck has posted a reply so the debate has begun.
  12. A theory must do two things it must explain what has been observed and it must be useful to predict the result of future experiments. A theory that fails in either way is discarded. In both cases the AGW by CO2 hypothesis has some big trouble. Please don't try to make it a theory. We need it to be much better, but I don't know if it needs to be discarded.
  13. WA I agree. BTW Have you had a chance to view any of the articles that I linked to on the volcanos thread? Every time I look for newer articles I run across another one on climate sensitivity to something or another. Spencer says it lower to CO2, Kay says it higher for TSI and the last article I posted a link to in volcanos says it's plate tectonics.
  14. sorry, my s key must be sticking in the up position.
  15. Pep I just finished reading the short version Beck draft. What did you find objectionable? Mizimi What web site are they posting this argument on?
  16. Yeah I've been looking. I think we may be running headlong in the wrong direction. The satellite data that was supposed to prove a positive feedback from CO2 causing increased water vapor in fact show the opposite. I don't say we are certain but it is starting to look like there is no way CO2 can be a large climate driver. Coupled with the paleo record clearly saying it isn't...
  17. The evolution of C4 plants happened around the Miocene/Pliocene interface when CO2 levels were lower than today and C4 plants began to develop.. C3 plants cannot cope with low CO2, they require 180 -220ppm for successful growth. Experiments indicate a 58% reduction in photosynthesis if the level is dropped from 380ppm to 150ppm and up to 90% reduction below 150ppm. C4 plants require a lower ppm value as they are 'more efficient': the first C4's were grasses. Before the appearance of grasses, most plants used phosphoglyceric acid (3 carbon atoms)to photosynthesise. Hence the name C3. Grasses, on the other hand, use oxaloacetic acid ( 4 carbon atoms) for photosynthesis, and are called C4 plants. As C4 plants were more efficient they began to dominate the planet creating vast eares of savannah and effectively locking up CO2. Thure Cerling has demonstrated that C4 plants "fixed" large volumes of CO2 from the atmosphere during photosynthesis and subsequently into the soil upon death. It is considered that this lowered the level of CO2 and thus GMT, resulting in the extinction of many of the large mammals. Keelings response to Becks paper: Beck reply:
  18. Mizimi Thanks
  19. Mizimi and Pep After reading both comments and the rebuttal I tend to agree somewhat with Beck, but also fail to see the relavence to sensitivity.
  20. Mizimi I am not familiar with C3 and C4 (except for the plastique kind) but from what you said I take it that pines are C3 and maples, elms and oarks are C4. What about the leafy evergreens like cedars, C3 or C4?
  21. QM: Plants are classed biochemically as C3, C4 and CAM. C3 plants are the earliest evolved class and include all trees, bushes, shrubs with high wood/lignin & tannin content. They are the source of coal. C4 plants evolved relatively recently (8mya) and essentially are the grasses..oats, wheat, barley,bamboo alfalfa and so on. They can be woody (bamboo) but use a 4-carbon molecule in photosynthesis, hence the name. CAM's are specialists...they have means to cope with stress...high Temp, low water or CO2 etc...and include cacti, succulents and so on. Because C4 plants are more efficient chemically than the others, they return LESS CO2 to the atmosphere during respiration (about 25% less than an equivalent C3)so eventually lock up CO2.
  22. Mizimi Ok, I thought you meant trees as I had read somewhere that some are better than others as carbon sinks. I also had read that grasses were better carbon sinks than trees but not why. Interesting, thank you.
  23. QM: I did mean trees as well as other plant types. Plants ( and trees) using C3 process are the oldest species; C4 plants are newcomers. So trees ( of all types ) are C3's. C3's can tolerate much higher levels of CO2 than C4's as in early epochs, but they cannot work with low levels of CO2 (under 220ppm for example). C4's can work with very low levels of CO2 because they concentrate the gas in tissue before using it. BUT they don't like very high CO2 levels according to recent research...though this is contended by others.
  24. Mizimi Thank you, I was not aware of that.
  25. Pep John's thread on Solar Cycles is also relavent to this thread. Naturally when I used this in the Arctic Sea Ice Melt thread I was attacked by alarmists who apparently did not read it.

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