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Sun & climate: moving in opposite directions

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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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Further viewing

Related video from Peter Sinclair's "Climate Denial Crock of the Week" series:

Further viewing

This video created by Andy Redwood in May 2020 is an interesting and creative interpretation of this rebuttal:

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Sun

Please check the related blog post for background information about this graphics resource.

Denial101x videos

Related lecture-videos from Denial101x - Making Sense of Climate Science Denial


Additional video from the MOOC

Expert interview with Mike Lockwood


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Comments 876 to 900 out of 1300:

  1. Eric (skeptic) @875, first, I think there may be a difference in definition. Specifically, when talking about thermal lag for CO2, we are talking about the period of time to reach 60% (or there about) of the equilibrium response. When we talk about thermal lag for seasonal temperature changes, we are talking instead about the time difference between the peak (minimum) insolation and the peak (minimum) temperature response. That is because the oscillating insolation does not leave enough time for 60% of the equilibrium response to be reached. Rather, the insolation falls below the equilibrium level of the current temperature long before it reaches that point. The same is certainly true for the solar cycle, and probably true for changes in TSI over the 20th century in general, which first fell, than rose to about 1950, then fell again, then rose almost as far, and then fell gradually. Consequently thermal lag for insolation probably measures the period to peak measurable response rather than the period to a certain percentage of equilibrium response as with CO2. The difference is not because of the different source of forcing, but because the CO2 forcing is increasing monotonically (note: CO2 forcing, not total or total anthropogenic forcing). Second, the level of the forcing for changes in TSI and especially for the solar cycle are not large, and certainly not nearly the same size as the CO2 forcing. Remember that the greatest change in TSI in the twentieth century (from 1910 to 1950) accounted for approximately a third of a slower warming than that at the end of the twentieth century which can be attributed exclusively to CO2 (but only in that the other factors canceled out). Consequently the peak solar forcing is at most a third of the peak CO2 forcing in the twentieth century, which means the resulting decadal temperature change from solar alone is not greatly different from the annual variation in mean global temperature. If the temperature is rising then falling due to an oscillating forcing, it will approximate to a sine wave. It will first rise slowly, then quite rapidly, and then slow down again. For a weak forcing, it is probable that only the change in temperature during the rapid rise will be statistically detectable, particularly if the forcing is very weak (solar cycle) or there are only one or two examples to test against (major TSI changes). Consequently the end of the peak measurable change of temperature will coincide with the end of that rapid rise rather than the actual peak which will be obscured by year to year temperature variations. Third, and particularly for the the solar cycle, because annual temperature fluctuations are large compared to those induced by the solar cycle, it is probable that after a short period of time a random fluctuation will bring the temperature up to the peak response point. From that point the higher (or lower) insolation will be acting to dampen departures from that temperature rather than lifting (or lowering) the temperature to that point. And as we have established, there is no thermal lag for that. Consequently the two month lag (which I and, more importantly as he has reasonable claim to expertise in this area, Tamino find surprising) may just be the average period until a random fluctuation shifts the temperature towards the effective equilibrium temperature. My point is not that any of these factors is shortening the "thermal lag" period for TSI variations including the solar cycle. It is that there are good reasons to expect weak, and fluctuating forcings to exhibit a reduced lag response both because their full response is never exhibited due to lack of time, and because noise can swamp out the more subtle parts of the signal. I do not suppose these are the only ways that can happen, and nor can I claim to know how much each factor is relevant in particular cases. But I do know that the difference between the thermal lag duration for CO2 and solar forcings is a function of characteristics of those forcings, not special pleading.
  2. Eric (skeptic) In comparing the lag of decades for CO2 and months for the 11 year solar cycle you appear to be confusing "equilibrium" and "instantaneous" responses of the climate. Think of the thermal inertia of the oceans as acting like a damper in a car suspension system; if you increase the weight of the car, it will slowly sink on its suspension at a rate depending on the damping. If you put a 100kg weight in the car, it doesn't immediately sink an inch, it takes a fraction of a second. If you fit stiffer dampers, it will take longer. So there is an "equilibrium" response of the suspension that is larger than the "immediate response" (it starts settling immediately, but it takes time to get to its equilibrium position). Now consider what happens if you drive down a cobbled street (i.e. a cyclic forcing), the damper then will attenuate the oscillation in ride height, and you will find there will be lag introduced in the ride height relative to the road surface, but there is no "equilibrium response" as the cobbles don't change the equilibrium ride height.
  3. Tom, I must take issue with your statement "Second, the level of the forcing for changes in TSI and especially for the solar cycle are not large, and certainly not nearly the same size as the CO2 forcing." Please double check these numbers, but 11 year TSI amplitude is 0.1% or 1366/1000/4 or 0.34 W/m2. For CO2 over 11 years it is 22 ppm or (22/280)*3.7 or 0.29 W/m2. That means they are roughly the same amplitude over that phase of the solar cycle. Dikran, perhaps you can check those numbers too, I don't see how the damping on the CO2 rise can be any different than the damping on the TSI oscillation. Aren't they exactly the same?
  4. Eric, the point is that you are confusing the instantaneous response with the equilibrium response. The climate starts responding to CO2 rapidly just as it does the 11 year solar cycle, but in the case of CO2 it eventually overcomes the inertia (as it is monotonically rising) but the 11 year solar cycle doesn't as it alternates phase far earlier than thermal inertia is overcome. If TSI gradually increased (rather than oscillated) it too would have an equilibrium response that would only be fully realised after several decades, but temperatures would start to rise immediately. I don't know if you have an engineering background, but it is the difference between the equilibrium response and transient response of a system described by differential equations. They are not the same thing.
  5. Eric, I think your comparison is apples and oranges. First, as to the cycle, while the change in amplitude could be 0.34 W/m2, it's not really fair to treat the minima as the baseline, so you're really talking about +/- 0.17 W/m2. It's also not a square cycle, jumping from minimum to maximum in one leap, so the duration of time spent at that full increase or decrease is low, with the majority of the cycle spent within 0.09 W/m2 or even less. Also, every positive swing has the negative swing, so any lag at all is going to be very muddled (with the counter/braking action starting before the original action is able to take effect). Second, for changes between cycles, the difference is even less than 0.34 W/m2, much less. In the past three cycles, the variation from the first to the third maximum (eyeballing it) looks to be less than one one hundredth of one percent, while the minima have no apparent change.
  6. Eric, Just to make it a little clearer, no net change in minima, and a net change in maxima of about 0.03 W/m2 i the past 33 years, would net out (since most of the time is spent in the basically unchanged ups and downs of the cycle) to probably an addtional 0.03 W/m2 for maybe 6 or 9 of those 33 years, or at best 1/4 of the time, meaning a net of 0.0075 W/m2... a completely inconsequential number.
  7. Eric, Whoa! Lastly, I just noticed that you bumped the CO2 forcing down to only consider the change in forcing, i.e. in the increase during an 11 year period. But the CO2 forcings are cumulative, where the TSI changes are not. It's hardly a fair argument to compare 11 years of TSI changes (which net to zero!) to 11 years of CO2 changes which pile on top of decades of previous change in the value. Those are not the two values under discussion (11 year change in CO2 versus 11 year change in TSI, which itself is probably less than 0.0025 W/m2 anyway -- you have to measure the areas under the two curves to get a true number).
  8. Sphaerica, your first post didn't really address my concern because you turned the 11 years of increase into a shorter interval of high solar. Then your second post changed the topic to secular solar changes and I have no argument with it (they are small). In your third post you resumed the original topic but missed my point which is quite simple: there is an interval of 11 years in which the TSI forcing increases roughly the same amount as CO2 does during that same interval. It is then balanced by the next 11 years of decreasing TSI forcing. Dikran, you are suggsting that the earth has a different thermal intertia to TSI changes than to CO2 changes. I don't see how that can be true. Tom, regarding your statement "Second, the level of the forcing for changes in TSI and especially for the solar cycle are not large certainly not nearly the same size as the CO2 forcing" would make sense if it was simply appended with "in total" or "since preindustrial" or "ongoing long term". Then we would all be able to violently agree.
  9. Eric (skeptic) @883, first, Sphaerica's 880 and 881 are I believe restatements of my first point in 886. So are Dikran's 877 and 879, though he states it with greater clarity and economy than I do. Second, I think the best way to state it is that the unrealized instantaneous forcing is very much larger for CO2 than for TSI changes associated with the solar cycle, and significantly larger than for TSI changes at any time in the twentieth century. By "unrealized instantaneous changes" I mean the change in total forcing due to a given factor at anytime minus the change in OLR due to changes in surface temperature at the same time. I take it that is what you mean by "ongoing long term forcing", and also what Sphaerica was describing in his 882. That being the case, we can all now agree furiously together on this point.
  10. Eric (skeptic) wrote: "Dikran, you are suggsting that the earth has a different thermal intertia to TSI changes than to CO2 changes. I don't see how that can be true." No, I am not suggesting any such thing. The thermal inertia of the earth has the same effect on warming due to TSI changes as it does on CO2 changes. The point is that you are comparing the equilibrium response to CO2 forcing with the transient response for TSI, so you are not comparing like with like. If TSI forcing was steadily rising just as CO2 radiative forcing is, then there would be a transient response (the Earth would start warming essentially immediately), but the full warming would not be realised for some decades (the equilibrium response). However, TSI is not steadily rising, it is oscillating, which is why the delay being discussed in relation to the 11-year solar cycle is not the delay before equilibrium is reached, it is a phase shift caused by the thermal inertia of the oceans. Until you understand the difference between a transient and an equilibrium response in a dynamical system, you are unlikely to resolve your confusion.
  11. Dikran, I think Tom explained it pretty well in 884. Past CO2 forcing plus thermal intertia (to warming) have produced an unrealized forcing which exceeds any natural forcing since secular natural forcings are all very small. Thus the GAT effect of such a forcing is much larger than the GAT effect of any cyclical natural forcing like TSI.
  12. Great Post! It's 2011, and we in the US are in the middle of another Summer heat wave and severe drought. I used a few arguments from this post to totally debunk someone in my office who was trying to use the "11-year solar cycle" argument to explain this drought.
  13. gcdem, The solar cycle has nothing to do with the Southern (especially Texan) drought. The main culpret has been the strong La Nina. Areas to the north experienced above normal precipitation (rain and snow), whereas southern areas were rain-starved. Similar occurrances accompanied past strong La Ninas, many of which were more severe than the current situation, particularly the mid 1950s.
  14. Hi all, Do you have a page dedicated to the Denialist claim that the IPCC itself admits it doesn't know what's happening with solar forcings at the following 2007 report page. IPCC 2.9.1 Uncertainties in Radiative Forcing
  15. Um, it's rather a long stretch from quantifying the uncertainties as of 2007 to "it doesnt know whats happening". As that reference points out, solar forcing is extremely well measured for last 25 years (direct measurement by satellite) but is "B" because of reliance on proxies prior to that. For more up to date look at the solar proxy uncertainties see this . Note that all forcings (indeed all scientific measurements) have uncertainties. What's important is the extent to which these can be quantified.
  16. I am not sure if any of you notice this or not, but the PMOD link goes to a data set that is a little too small of deviation for solar data collected in Earth orbit with daily entries. That is to say, the Earth's orbit is elliptical. For part of the year we are closer and the other half farther away. This results in a difference of about 90 W/m^2 between minimum and maximum. The data on PMOD at most varies by a few W/m^2 in a year. If you are measuring values on 22DEC2009 that are within 1 W/m^2 of values on 22JUN2010, then you have some issues with your data. That difference should be pushing 90 W/m^2. The difference in r value for the intensity calculations is about 5 million km. So, maybe the sources for this article should be revised.
  17. Thanks Scaddenp. One query regarding the forum software: every thought of switching to Wordpress? Wordpress is great software and has BBpress forums as a plug-in now. Commenting could have all the power of BBpress (or SMF or Phpbb3 or whatever other open source forum software you want).
  18. Disregard the last comment about Wordpress... I just realised how much work you've already put into the ipad and iphone apps and would hate to put you through all that again. (Not sure if Wordpress has simple translation into these formats but there you go). I just love powerful forum software, because... well... I didn't even get an email last time someone replied?
  19. This next argument seems to be another version of "It's the sun" that good old Willie Soon (and his $million from Exxon) have written. New Willie Soon paper Does anyone know any peer-review work on this yet? Is the journal it is in actually an authentic climate journal? Is it legitimate science about a LOCAL Chinese phenomenon or a hyped up local phenomenon that fraudster Denialists are using to try and confuse people about GLOBAL climate change?
  20. I've read the abstract of the Soon paper you linked to Eclipse. The temperature trends observed in China seem consistent with what is known about the 20th Century temperature trends in general IIRC - as a result of global brightening and dimming. So he may have that part right at least.
  21. And besides,the paper was about *China* and about the 20's and 40's for some reason. It's not as if he's discovered something controversial about the *globe now* is it? Cheers.
  22. Soons paper sounds to me like the results of a search for statistically significant trends and association with solar forcing region by region - which of course invalidates the test of statistical significance (unless multiple hypothesis testing issues are properly dealt with).
  23. Continuing from here. EtR's sunspot graph clearly shows the 1950s solar maximum; since then solar activity has in fact declined (hence the descriptive term maximum). A simple straight lines fit doesn't capture that important detail and is therefore irrelevant.
  24. To illustrate Muoncounter's point @898:
  25. Muon, Yes, solar cycle 19 was definitely the highest of the 20th century. However, cycles 21 and 22, in the 1980s and 1990s, were the next two highest, significantly surpassing anything during the early 20th century. The point is that sunspot activity was still high during the last portion of the 20th century. To expect temperatures to decrease based on the drop from a very high to just a high value would be comparable to expecting temperatures to drop because we added less CO2 to the atmosphere this year than last. A straight line fit does not capture the temperature profile of the 20th century, but does that negate the fact that an increase has occurred?
    Response: [Dikran Marsupial] Re your second paragraph, it is well know that there are multiple forcings that affect climate, hence nobody would expect a straight line fit. Please be less opaque in your posts as such obfuscation gives the impression of trolling.

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