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Humans and volcanoes caused nearly all of global heating in past 140 years

Posted on 30 May 2019 by dana1981

Emissions from fossil fuels and volcanoes can explain nearly all of the changes in Earth’s surface temperatures over the past 140 years, a new study has found.

The research refutes the popular climate denial myth that recent global warming is merely a result of natural cycles.

Those arguments have always suffered a key physical flaw, namely that cycles are cyclical. For example, El Niño events, which temporarily raise global surface temperatures by bringing warm water up to the shallow ocean layer, are offset by La Niña events, which have the opposite effect. While a given decade might have more El Niño or La Niña events, resulting in a short-term surface warming or cooling, over the long term their effects cancel out.

However, climate scientists have had a difficult time explaining exactly what caused a warming event in the early 20th century, between about 1910 and 1945. The average of the climate model runs incorporated in the last IPCC report only accounted for about half of the measured global surface warming trend during that period, and a study published last year suggested the other half could be due to natural cycles.

Contrarian scientists like Judith Curry, who is frequently invited by Republicans to testify before US Congress, have often used this discrepancy to cast doubt on the expert consensus on human-caused global warming, arguing that “until we can explain the early 20th century warming, I have little confidence IPCC and [National Climate Assessment] attribution statements regarding the cause of the recent warming.”

The new study, published in the Journal of Climate, tackles the discrepancy in part by addressing an issue with ocean temperature data during the second world war, when measurements were more often made from warmer engine room intakes than from buckets lowered over the side of ships. This has resulted in a bias, inflating estimated surface temperatures in the early-to-mid 1940s. The new study removed this bias by focusing on temperatures along continental and island coastlines.

Arctic temperature data has also long been problematic. There are relatively few temperature monitoring stations in the region due to its remoteness, but due largely to disappearing sea ice decreasing the region’s reflectivity, the Arctic is the fastest-warming part of the planet.

Two of the co-authors of the new study, Kevin Cowtan and Robert Way, previously made strides in addressing these coverage gaps by using improved statistical interpolation methods. The new study goes further, by incorporating Met Office Hadley Centre Arctic sea ice data.

Accounting for the area of Arctic ocean covered by sea ice is an important factor, as lead author Karsten Haustein explains: “If sea ice is treated as ocean, the temperature cannot go below zero (per definition). If it is treated as land, the temperature can fall as low as -50C in winter given there is virtually no interaction with the ocean water anymore. Since warming trends over the Arctic are higher than anywhere else, overall land warming trends will be higher too if sea ice is treated as land. This is by virtue of winter temperatures not falling as low as they used to anymore.”

The authors then compared the improved global surface temperature data to climate model runs incorporating influences from human greenhouse gas and aerosol pollution, volcanic eruptions, and changes in solar activity. Overall they were able to explain more than 90% of the temperature variation over the 140-year record.

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Comments 1 to 9:

  1. Dana, it's great to see another article of yours in the Guardian!

    The headline is misleading as it implies that 1.) volcanoes cause warming, and 2.) that the warming they cause is comparable to the impact of human emissions. While the article explains that a lull in volcanic activity in the mid-20th century caused less cooling, describing this as a heating effect can misinform laypeople scanning the headlines.

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  2. Agree with BB.  While the article is great and the headline is technically correct it gives a bad message that volcanos are a big factor in long term warming, and it will delight climate denialists. We know people often only read headlines.

    It might have been better to word it differently like "new study better explains early 20th century and recent arctic warming"

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  3. This is a good article and I appreciate the information. However, I still have a problem with the IPCC 2014 report. (1) On page 43 of the Synthesis report there is a graph showing the predicted degrees C change in temperature per decade of climate models for 1998-2012. All of the models are predicting temperatures that are too high for that time frame excepth possibly one. Most of them get the number many times too high - like factors of 3 to 8 all the way up to 10. I don't have any problem with constructing a model of past climate and including effects as they are better understood. I do have a seious problem with using such models to extrapolate far into the future. This is particularly true when the extrapolated models are so far off at the point where they go from modeling the past to predicting the future.  (2) Another question I have that is a problem for me is: "What is a climate temperature number?"  Core samples, whether ice cores or sediment cores, generally  give proxy temperature numbers that are averages over many years - sometimes one or two thousand years. So is a climate temperature an number measured today somewhere in the middle of the Pacific ocean? Or maybe an average over a year. Or averages of global temperature measurements over a year or a decade or a century, ... , or maybe a millenium?  (3) Finally, there is another interesting graph in the 2014 IPCC report on page 43 of the summary report. This graph shows that the OECD-1990 Countries have held their emissions nearly constant as a group since about 1970. That same graph shows that  Asia has been increasing their emissions by about 12 Gt/Yr over the same period. I think that this points to a serious problem over which we have very little control. A switch by Asia from coal to natural gas would probably hit the emissions problem where a punch would do the most short term benefit.

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  4. Higgijh @post3 ,

    (3)  My apologies for fumbling your IPPC reference, but I turn up a completely inappropriate graph at Page 43.   Would you be kind enough to insert your correct graph into the thread here?  [Remembering the 500px width limit.]   On second thoughts, it would be better for you to select a different thread ~ one where the question of Asian coal vs gas usage is on-topic (as it is not really relevant to the headline topic here of Humans and Volcanoes causing global heating since 1880 ).


    (2)  There is always the question of localization effects and time-resolution effects, in the assessing of temperature proxies in ice and sediments.   But broadly speaking, these proxies are useful even when time-resolution is low.

    We know that the climate only changes when something causes it to change ~ so in the absence of major factor changes in the last 10,000 years, we can [for example] be confident that the present-day world temperature is distinctly hotter than the Medieval Warm Period or the Roman Warm period or the "Holocene Optimum".


    (1)  Higgijh, this IPCC Page 43 seems the correct one you mean for (1).   But I am entirely unclear on what difficulties you are having with it.

    Climate trends are best assessed over a period of usually 30 years (or more) ~ so it is rather unsurprising that the Figure (c) over 60 years shows a good concordance between observations & models.   Likewise it is not surprising that the short periods Fig. (a) 1998-2012 and Fig. (b) 1984-1998 , show observation/model disparity, since "natural internal variability" is more dominant during such very short periods.

    The construction of climate models serves two purposes :-

    #  helping the assessment of individual climate factors [e.g. evapo-transpiration]

    #  projecting what may happen in the future, by a way which is likely to be much better than a guess ( = the equivalent of holding up a wetted finger to the breeze ).

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  5. I appreciate the response I've gotten on my comment.

       Note that although I reference page 43 twice, one reference is from the Synthestis report and the other is from the Summary report.

    My current viewpoint.  (A) Climate change is real. Anyone who says differently has to account for the absernce of the glaciers over the Great Lakes. (B) Carbon Dioxide is a green house gas and humans are pumping a lot of it into the atmosphere. So humans must be contributing to warming. (C) The climate system is a very compelex system that nobody fully understands. (D) Major changes in climate temperature that have brought on past ice ages is primarily driven by earth orbital cycles with periods of 23,000 years, 42,000 years, and 100,000 years.  (E) Climate temperature proxys over the last million years indicate that peak temperature peaks are often (not always) very sharp (with respect to a 1000 year grid). (F) The earth is just now coming out of a peak in the temperature variations caused by the orbital cycels. (G) When proxy temperature information inherently averages over 1000 years, the indicated peak temperatures over a 100 year period are drastically smoothed and diminished.

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  6. Higgijh @post5 ,

    If I have correctly understood your thoughts : your are basically concerned by the low time-resolution of past temperature (proxy) records & what may be inferred from them.

    Certainly, the time-resolution becomes fuzzier, the farther back in time we explore.   We can delineate the past 1000 - 2000 years of climate changes rather more exactly than the past 10,000 years or the 800,000 years (of the ice-core records) or the past 500 million years (with very low time-resolution in say the Ordovician period).

    Yet the laws of physics haven't changed during all that time, and we can see [for example] that Newtonian Laws of Motion must have applied just as well during the Ordovician as during the current Holocene.

    How does that apply to world temperature changes?   If we look at the past 10,000 years (of the Holocene interglacial) we see a flat plateau of about 5,000 years [the "Optimum"] followed by the latest 5.000 years showing a gradual decline in temperature, which would eventually have triggered a new glaciation in about 20,000 or 30,000 years' time or more (an "abnormally" long interglacial, owing to the current low-ellipticity of Earth orbit).   Or at least, that is what would happen, without the human [CO2] intervention of the past century or two.

    The temperature record of recent centuries shows that the reaction to a major volcanic eruption is a very brief world temperature dip (less than 5 years).   And the reaction to a major diminution of insolation (a Grand Solar Minimum) is a much more prolonged dip ~ but only about 0.3 degrees.   These sorts of excursions explain why the "shape" of the Holocene resembles a relatively smooth plateau.   The "wiggles" of temperature (such as the Medieval Warm Period or the Little Ice Age) are very minor indeed, against the general background.

    Higgijh ~ going farther back in time, if you had been alive during the time of the Younger Dryas (and miraculously you lived for twice Methuselah's age! ) you would have seen a large excursion of world temperature during a 1000 years.   But that change was gradual, compared with the rocket-like rise in temperature of the immediate 50 - 100 years past.   And the cause of the Younger Dryas would have been very obvious to you (to you and your team of observer-scientists).   The point being, that "low time-resolution" is not a problem in seeing the results of major climate factors.

    Similarly, going back through 800,000 years, you see the climate alter in a cyclic way (Milankovitch insolation "forcing changes" of up to 0.7 watts/m2 , triggering a CO2 greenhouse change much larger than that).   Again, the "smoothing" of the time-resolution record is not a problem for understanding the history.

    For a separate additional effect to produce a rapid spike (up or down), there would have to be some large & powerful short-term causation for temperature change.    Just as in Newtonian terms, a mass does not change velocity unless it is acted upon by a force ~ so too for climate : climate does not change unless something causes it to change.

    Which is why - in the observed absence of major climate factor changes - it does not matter that the (proxy) climate record has a resolution far worse i.e. far fuzzier than annual / decadal / or centennial, as the case may be.

    Higgijh, I hope I have addressed your basic concern.   But perhaps you have deeper unexpressed concerns?

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  7. Higgij

    I'm not sure what you are really getting at. I agree with eclectic. However I will throw in a couple of comments:

    You expressed a concern that the early IPCC modelling did not predict the "pause" after 1998 (if I interpret you correctly). Scientists have always been up front that modelling cannot accurately predict relatively short periods like 10 years because they are influenced by natural variation. Eg clearly no modelling can predict volcanic eruptions or accurately predict a semi regular cycle like el nino, however modelling can predict longter term trends. In fact the pause does easily fit within error bars of the models see here.

    "(F) The earth is just now coming out of a peak in the temperature variations caused by the orbital cycels. "

    Not really refer here. Earth has been in a cooling phase for about 5,000 years and this has only been seriously interrupted by the warming spike since 1900.

    "(G) When proxy temperature information inherently averages over 1000 years, the indicated peak temperatures over a 100 year period are drastically smoothed and diminished."

    There is not enough data to get every short term temperature spike in the paleo record, however I recall reading somewhere that they use a random data gathering process which means its likely any large spike of 100 years would be captured. But even if past temperature record has short periods of rapid warming of 100 years comparable to recent decades since 1900, it would have to have an explanation, possibly intense volcanic activity. Volcanic activity was often very intense and protracted in Earths early history.

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  8. higgijh @5,

    Adding a few numbers to the comment of Eclectic @6, the Vostok temperature data (for instance here) gives samples at least every 100 years back to beyond the last interglacial (the Eemian) and even back two more interglacials is still providing samples at least every 300 years. This data allows us to see that the current interglacial is uniquely long. The three previous interglacials peaked in hundreds of years while the present interglacial has lasted 10,000 years.

    I would also add a few other comments:-

    (A) A lack of glaciation over the Great Lakes is not a very useful marker for the climate change of the last century or so.

    (D) The Milankovitch cycles ar not what "drives" ice ages, they are what 'triggers' ice ages. The 'drivers' are albedo (sunlight reflected away due to increased/decreased snow cover) and greenhouse gas concentrations. Mankind's GHG emissions have put pay to the ice-age cycle cooling & growing glaciation of the high northern latitudes so the coming ice age ain't gonna happen.

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  9. Just one other further point. The milankovitch forcing for ice ages is very slow. At 65N (where the changes in solar insolation make the difference between summer melt or not), the change is of order of 0.01W/century. By contrast, injecting GHG into the atmosphere at the current rate is producing a forcing of order 4W/century over the entire globe.

    I am always suspicious of statement like "The climate system is a very compelex system that nobody fully understands. " You will be hard pressed to find a scientist that would claim to "fully understand" any physical system. We do however understand a great deal about physical systems including climate. For instance, we can say with enormous confidence that if you change the incoming energy reaching the surface than the climate will change in response and furthermore, the amount of change will be positively (not necessarily linearly) related to the amount of change in that incoming energy. Scientists are a skeptical bunch butthey are extremely wedded to concept of conservation of energy.

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