The 2007-2008 Global Cooling Event: Evidence for Clouds as the Cause
September 26th, 2009 by Roy W. Spencer, Ph. D.
As I work on finishing our forcing/feedback paper for re-submission to Journal of Geophysical Research – a process that has been going on for months now – I keep finding new pieces of evidence in the data that keep changing the paper’s focus in small ways.
For instance, yesterday I realized that NASA Langley has recently updated their CERES global radiative budget measurement dataset through 2008 (it had previously ran from March 2000 through August 2007).
I’ve been anxiously awaiting this update because of the major global cooling event we saw during late 2007 and early 2008. A plot of daily running 91-day global averages in UAH lower tropospheric (LT) temperature anomalies is shown below, which reveals the dramatic 2007-08 cool event.
I was especially interested to see if this was caused by a natural increase in low clouds reducing the amount of sunlight absorbed by the climate system. As readers of my blog know, I believe that most climate change – including “global warming” – in the last 100 years or more has been caused by natural changes in low cloud cover, which in turn have been caused by natural, chaotic fluctuations in global circulation patterns in the atmosphere-ocean system. The leading candidate for this, in my opinion, is the Pacific Decadal Oscillation…possibly augmented by more frequent El Nino activity in the last 30 years.
Now that we have 9 years of CERES data from the Terra satellite, we can more closely examine a possible low cloud connection to climate change. The next figure shows the changes in the Earth’s net radiative balance as measured by the Terra CERES system. By “net” I mean the sum of reflected shortwave energy (sunlight), or “SW”, and emitted longwave energy (infrared) or “LW”.
The changes in the radiative balance of the Earth seen above can be thought of conceptually in terms of forcing and feedback, which are combined together in some unknown proportion that varies over time. Making the interpretation even more uncertain is that some proportion of the feedback is due not only to radiative forcing, but also to non-radiative forcing of temperature change.
So the variations we see in the above chart is the combined result of three processes: (1) radiative forcing (both internal and external), which can be expected to cause a temperature change; (2) radiative feedback upon any radiatively forced temperature changes; and (3) radiative feedback upon any NON-radiatively forced temperature changes (e.g., from tropical intraseasonal oscillations in rainfall). It turns out that feedback can only be uniquely measured in response to NON-radiatively forced temperature changes, but that’s a different discussion.
The SW component of the total flux measured by CERES looks like this…note the large spike upward in reflected sunlight coinciding with the late 2007 cooling:
And here’s the LW (infrared) component…note the very low emission late in 2007, a portion of which must be from the colder atmosphere emitting less infrared radiation.
As I discuss at length in the paper I am preparing, the physical interpretation of which of these 3 processes is dominant is helped by drawing a phase space diagram of the Net (LW+SW) radiative flux anomalies versus temperature anomalies (now shown as monthly running 3-month averages), which shows that the 2007-08 cooling event has a classic radiative forcing signature:
The spiral (or loop) pattern is the result of the fact that the temperature response of the ocean lags the forcing. This is in contrast to feedback, a process for which there is no time lag. The dashed line represents the feedback I believe to be operating in the climate system on these interannual (year-to-year) time scales, around 6 W m-2 K-1 as we published in 2007…and as Lindzen and Choi (2009) recently published from the older Earth Radiation Budget Satellite data.
The ability to separate forcing from feedback is crucial in the global warming debate. While this signature of internal radiative forcing of the 2007-08 event is clear, it is not possible to determine the feedback in response to that temperature change – it’s signature is overwhelmed by the radiative forcing.
Since the fluctuations in Net (LW+SW) radiative flux are a combination of forcing and feedback, we can use the tropospheric temperature variations to remove an estimate of the feedback component in order to isolate the forcing. [While experts will questions this step, it is entirely consistent with the procedures of Forster and Gregory (2006 J. Climate) and Forster and Taylor (2006 J. of Climate), who subtracted known radiative forcings from the total flux to isolate the feedback].
The method is simple: The forcing equals the Net flux minus the feedback parameter (6 W m-2 K-1) times the LT temperature variations shown in the first figure above. The result looks like this:
What we see are 3 major peaks in radiant energy loss forcing the system: in 2000, 2004, and late 2007. If you look at the features in the separate SW and LW plots above, it is obvious the main signature is in the SW…probably due to natural increases in cloud cover, mostly low clouds, causing internal radiative forcing of the system
If we instead assume a much smaller feedback parameter, say in the mid-range of what the IPCC models exhibit, 1.5 W m-2 K-1, then the estimate of the radiative forcing looks like this:
Note the trend lines in either case show a net increase of at least 1 W m-2 in the radiant energy entering the climate system. The anthropogenic greenhouse gas component of this would be (I believe) about 0.4 W m-2, or a little less that half. I’ll update this if someone gives me a better estimate.
So, what might all of this mean in the climate debate? First, nature can cause some pretty substantial forcings…what if these occur on the time scales associated with global warming (decades to centuries)?
But what is really curious is that the 9-year change in radiative forcing (warming influence) of the system seen in the last two figures is at least TWICE that expected from the carbon dioxide component alone, and yet essentially no warming has occurred over that period (see first illustration above). How could this be, if the climate system is as sensitive as the IPCC claims it to be?
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To recap on the OT:
Leif: “It is also well-known that candles do not spread light, rather they suck up the dark, just look at their wicks.”
jorge: “A noted astronomer once assured me at a party that days were “longer in the zummer und shorter in the vinter, because heat expands und cold contrakts!”
Leif: “Of course, and the Moon is more important than the Sun, because is shines at night when it is dark, and we need the light more.”
I’d like to add, attribution unknown:
The northern hemisphere is warmer than the southern hemisphere because heat rises.
Speaking of CO2 from an atricle;
“It obviously hasn’t even crossed the mind of Ms Jackson’s prejudiced script-writer that the moral current is in fact running in Australia’s favor – for, by supplying third-world countries with the means to generate cheap electricity, Australia is in fact providing them with the only support there is that will allow them to lift themselves out of poverty. As other writers have commented, to intentionally obstruct development in third-world countries by depriving them of the right to use cheap, coal-fired power generation is a type of genocide; in essence, in order to expiate the consciences of comfortably-off middle class moralists in western nations, millions of underprivileged people are going to die.”
Media Ecoevangelists
http://www.quadrant.org.au/blogs/doomed-planet/2009/09/media-ecoevangelists
Pertaining to my previous post; It is important to get the perspective correct before you convey the message to the general public.
Nasif Nahle (19:46:45) :
the thermal energy absorbed by the gravity field, for example; however, we don’t know a bit about it because we have not gone yet beyond our near surrounding cosmos.
Is utter nonsense.
The gravity of the Earth attracts everything with mass floating in the atmosphere. Is that not true?
When the clouds in the atmosphere disperse without producing a major rain event; Is that the reason why we experience a rise in the level of humidity on the surface?
Leif Svalgaard (20:19:21) :
Nasif Nahle (19:46:45) :
the thermal energy absorbed by the gravity field, for example; however, we don’t know a bit about it because we have not gone yet beyond our near surrounding cosmos.
Is utter nonsense.</i
I don’t think so. It is simply an attempt to explain the essence of the gravitational field on the flow of heat (energy in transit) and the burden of energy transferred from a system which absorbs heat from an external source effect. My explanation depends on both Newtonian and Relativistic Cosmology.
We know that energy is released whenever a gravitational field is created by a global effect of energy removal, although we know also that the interchange of gravitational energy is quite lower than the energy at rest. From a cosmological viewpoint, the total gravitational energy is dominant.
Hartnett, James P., Irvine, Thomas F. Advances in Heat Transfer, Volume 21. 1991. Academic Press, Limited. San Diego, CA.
I am sorry… I forgot to include a reference for my next assertion:
“I don’t think so. It is simply an attempt to explain the essence of the gravitational field on the flow of heat (energy in transit) and the burden of energy transferred from a system which absorbs heat from an external source effect. My explanation depends on both Newtonian and Relativistic Cosmology.”
Here is it:
http://www.math.tulane.edu/~dupre/einsteq8.pdf
Scott A. Mandia (16:15:47) :
Ah, yes I understand. I don’t think that Dr. Spencer is assuming that the increased SW signal is due to low cloud cover, he is merely discussing likelyhoods. Low cloud cover is the likely explanation. SW radiation is reflected sunlight, and low cloud (water vapor) cover is the strongest reflector. High Cloud (ice crystal) cover isn’t as reflective of the incoming SW, however it is more reflective of outgoing LW radation.
Low cloud cover tends to cause cooling by reflecting sunlight (SW) back to space, High cloud cover tends to cause warming by reflecting the earth’s radiate (LW) heat back down. Naturally there could be other explanations such as volcanic eruptions etc., but low cloud cover is what’s likely.
pochas (19:37:35) :
bill (18:06:45) :
“I’m confused
LW + SW shows continual energy gain (average) fro 2000 to 2008 with a big gain at end of 2007. I.e. there should be a continual temp increase with big shift upwads in 2007.”
This confused me also. Dr Spencer does not use the standard convention that heat gained by the system is a positive quantity. With the standard convention LW and SW would be negative quantities, indicating heat leaving the system. But here they are positive, so that the increase at the end of 2007 for example indicates cooling not heating. With the standard convention the trend lines in the last two figures would have the “right” slope to indicate warming (upward instead of downward).
The values are denote what is being measured by the satellite. A positive trend at the satellite is a negative trend in the system.
if clean air acts led to global warming
Clean air acts may have had some warming effect, but primarily they led to to the appearance of global warming in the 1970s to the 1990s, because of their effect on minimum daily temperatures explained above.
Leif Svalgaard (12:41:41) : No, they wouldn’t, because the heat transfer depends on the temperature difference, which would decrease [and go sway] as the oceans heat up.
Right! Another point is that the air temperature would decrease faster than the ocean temperature would increase, as the thermal mass of the oceans is vast compared to the thermal mass of the air. Equations are.
m_o•cp_o•dT_o /dt = Qin_o – Qout_o (heat balance oceans)
m_a•cp_a•dT_a/dt = Qin_a – Qout_a (heat balance air)
Here, “o” denotes oceans and “a” denotes the air. Changing the temperature from T1 to T2 could be roughly approximated by;
T_o(t) = T1 + [T0 – T1] exp(-t/tau_o)
T_a(t) = T1 + [T0 – T1] exp(-t/tau_a)
Where the thermal time constants are
tau_o ~ m_o•cp_o
tau_a ~ m_a•cp_a
We all know that the thermal mass (m•cp) is much larger for the oceans than for the air, so when the oceans are heated by the air the temperature in the oceans will increase slowly while the temperature in the air decrease quickly. When the temperatures are the same the heat transfer terminates.
This also means, of course, that the so called anthropogenic global warming of the air would be increasing the thermal energy in the oceans extremely slowly – when a small thermal mass increases the temperature of a large thermal mass thermal equilibrium is quickly reached and the heat transfer terminates. Think it over….
Nasif Nahle (21:31:17) :
the thermal energy absorbed by the gravity field
Is still utter nonsense, in spite of your references that do not address this. Perhaps, help us by extracting the precise statement from the reference you think supports your statement and posting it here.
Nasif Nahle (17:00:40) :
P Wilson (13:31:43) :
tallbloke (03:30:26)
Heat isn’t an easy thing to understand. In a liquid, it will asymptotically approach a state where all energy is evenly distributed. In other words, in nature there is a tendency to the dissipation (energy loss). If you heat to 70C a pan of water in a totally isolated environmment, considerably larger than the pan and stove ( a totally sealed kitchen) the heat, after the heat source has been switcced off, will disippate, as energy can change form one form to another. Even in a vacuum flask where convection and conduction is prevented its energy will degrade. Three days later, why isn’t it still at 70C? Degradation of energy is the essence of entropy
=====================
The only way to interpret entropy is as the means by which we measure the amount of energy dispersed or diffused out to more available microstates in a process.
The degradation of the energy consists on the transformation from one form of energy into another form that would not be available for doing work in our limited cosmos.
======================
P Wilson. Your analysis is correct, but questions of scale and position have to be addresses when moving from kitchen cupboard analogies to the Ocean air system. For example, the pan of water or thermos flask radiate evenly on all sides.
The oceans are insulated by a hot planetary core on one side, and from cold space by the air on the other side. The Ocean gains heat from the sun, it loses it to the air far more readily than the seabed. The oceans have as much thermal capacity in the top two metres as the entire atmosphere above it.
The air has a warm ocean under it and cold space above it. Hot air rises. The atmosphere loses heat to cold space far more readily than to the warm ocean. If the air temperature worldwide fell from an average of 13C to freezing point, and all the heat energy went into the oceans, it would warm the oceans by around 0.008C.
The energy cycle goes from sun to sea to sky to space.
Changes in global air temperature lag changes in sea surface temperature.
Conclusion: The oceans are the major player in the earth’s climate system, not the air and any trace gases it may contain.
bill (18:06:45) :
I’m confused
LW + SW shows continual energy gain (average) fro 2000 to 2008 with a big gain at end of 2007. I.e. there should be a continual temp increase with big shift upwads in 2007.
BUT UAH lt shows a temp drop at this point.
Any explanation greatfully received.
Climate is more complicated than you’ve been led to believe.
High cloud is generally accepted as warming
Low cloud reflects SW during dayligh. BUT low cloud also retains LW and this predominates at night (no SW to reflect) i.e. cloudy nights = warm nights
So what is the forcing of low clouds? Do low clouds disappear at night?
Looking at the graphs above the word appliead to the pos and neg radiation balance explain their effect and is as I would expect. They show a decreasing loss of SW + LW from the sysytem. Incoming TSI has been constant from 2000 to 2003 and falling since then. Is there any change in lw/sw mix of TSI over this period?
Assume the albedo/blanket round the earth retains a constant % of TSI then as TSI decreases the magnitude of the imbalance should decrease. But the plots show an increasing magnitude. Why?
The plots show in my view radiation being retained in the system = higher temps. What is retaining it? Why not GHGs? Why are these dismissed?
tallbloke (00:45:42) : Conclusion: The oceans are the major player in the earth’s climate system, not the air and any trace gases it may contain.
Exactly! See my post Invariant (23:35:23).
tallbloke (00:45:42) :The energy cycle goes from sun to sea to sky to space.
Changes in global air temperature lag changes in sea surface temperature.
As you uggest the warm air does not heat the oceans significantly.
However, the oceans are not always hotter than the air and consequently will not transfer heat from ocean to air. Hot air WILL transfer heat to water. Only air movement will cool the surface through evapouration in these conditions. The air is quickly heated by insolation (otherwise there would be no day night variation. This maximum air temp will depend on its surroundings. and in general will heat a fixed number of degrees (set by insolation) above the heatsink temperature. This heatsink will be ocean, land, snow, tarmac. e.g.
sea temp =20C surface air temp=25C or in same insolation/wind conditions
sea temp =10C surface air temp=15C
In no case is the ocean heating the air. The heat is travelling from air to ocean in both cases. BUT the ocean is controlling the temp.
It is perhaps worth saying that whilst the ocean is not losing heat to the air it is still gaining energy from insolation and warming (very slowly due to its mass) In UK swiming in the sea is not sensible until well into the summer and ccertainly does not warm instantly on cloud cover disappearing.
tallbloke (00:56:02) :
Climate is more complicated than you’ve been led to believe.
I have no beliefs! I have a small UNDERSTANDING.
Specncer in the entry is making assumptions in my view that did not agree with the plots e.g. lower temps give less outgoing radiation (true of course). But surely so would more thermal resistance between the satellite and the planet surface?
bill
“The plots show in my view radiation being retained in the system = higher temps. What is retaining it? Why not GHGs? Why are these dismissed?”
There are two reasons for less LW radiation leaving the system: retention and/or a cooler atmosphere. Nothing is being dismissed.
Now why would the atmosphere get cooler when more LW radiation is retained? It can get cooler when less radiation comes in and that can happen if more SW radiation is reflected out to space–which these graphs showed has happened and Spencer thinks this is due to more low lying clouds.
As you can see from the graphs there’s no perfect symmetry between temperature and radiative balance. This is because, as spencer found, there’s a delay in radiative forcing that causes a change in temperature. But changes in temperature cause feedbacks which also change temperature and these changes are immediate. And not all changes in temperature are due to radiative forcing.
Thus it’s a bit more complex than a one-to-one relationship between outgoing radiation and atmospheric temperature.
Northern hemisphere temperatures dominate global temperature. If a drop in the solar signal occurs in the Northern Hemisphere winter it will have a marked affect on global temperature. If such a drop occurs in Northern Hemisphere summer, as happened in mid 2004, very low temperatures were noted in the Southern Hemisphere, but the impact on global temperature was much less. Changes in the solar signal can be very brief, as in mid July this year, when a sharp drop produced a very heavy uplift in rain for the Northern Hemisphere, and very cold conditions in S. America, Australia and New Zealand. Temperatures before and after this notch (June and August) were generally above normals everywhere. It is the timing and strength of these changes in the solar signal that are driving the cloud cover levels, in a similar way that they do with precipitation levels, which is a temperature drop in summer brings a rainfall jump, while a temperature drop in winter brings a dry period, and visa versa for a temperature raise.
Syl (03:57:14) :
There are two reasons for less LW radiation leaving the system: retention and/or a cooler atmosphere.
Agreed.
It can get cooler when less radiation comes in and that can happen if more SW radiation is reflected out to space
Agreed
–which these graphs showed has happened
The plots show more SW radiation in peaks 2004 and 2007 but in general it is a reducing level of outgoing SW radiation that reached minimum outgoing in early 2008.
Average insolation for the Earth is approximately 250 watts per square meter and varies by 0.1% =.25w/m^2
The drop in SW radiation away from the earth in the plots shows almost 2W/m^2 drop. ten times that caused by the peak to minimum TSI over the time of the plot.
and Spencer thinks this is due to more low lying clouds.
I assume that the 2007 peak (reflection of SW away from earth) is what is refered to here. The overall lowering of SW reflecting away can therefore be ascribed to less lower cloud cover over the 9 years???
bill (02:23:42) :
The problem with this theory is that oceans have a high heat capacity – meaning that it takes a lot of energy to heat the oceans by 1C than something with a lower heat capacity. Air doesn’t have much heat capacity, and doesn’t retain much heat. For this reason, warmer air does not pentrate cooler oceans. Only the sun can do that. Thats partly why even on a hot summer day, oceans at the beach are cooler than the air, the sand and the promenade.
Primarily, oceans heat the air during evaporation. During evaporation, large amounts of heat, c02, and water vapour are released.
P Wilson (05:56:38) :
Primarily, oceans heat the air during evaporation. During evaporation, large amounts of heat, c02, and water vapour are released.
Don’t think so
Cold sea will never heat warm air. Cold sea will control warm air temperature acting as a heat sink. measuring air temp from sea surface at 20C to a couple of meters above the sea will show a decreasing temp as the sea surface is approached reachin 20C at the surface.
if at say 2metres above the sea the temp is 25C and sea surface temp is 20C (ignoring air circulation then chnging sea temp by 1C will change air temp by 1C. But it is not heating the air. With air temp below se temp the sea will increase the air temp losing temp as it does so.
Air movements will rip molecules off the surface of the ocean (increase evaporation) and cool it through latent heat of evaporation. – Remember the science experiment blowing air through alcohol causes the alcohol to cool to freezing simply through latent heat of evaporation of alcohol. Question is does the blown air get hotter? Not sure but I do not think so. It will become more humid however.
This is rather pretty!
http://www.colorado.edu/physics/2000/bec/evap_cool.html