Q: What percentage of global warming is due to human causes vs. natural causes?

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"Q: What percentage of global warming is due to human causes vs. natural causes?"

A: Probably almost all of it

There still seems to be some confusion on this basic question.

A year ago, NASA scientist Gavin Schmidt was asked on RealClimate:  “What percentage of global warming is due to human causes vs. natural causes?”  His answer is straightforward:

Over the last 40 or so years, natural drivers would have caused cooling, and so the warming there has been “¦ is caused by a combination of human drivers and some degree of internal variability. I would judge the maximum amplitude of the internal variability to be roughly 0.1 deg C over that time period, and so given the warming of ~0.5 deg C, I’d say somewhere between 80 to 120% of the warming. Slightly larger range if you want a large range for the internal stuff.

Absent the increasing GHGs, we probably would have cooled, since

  1. We’ve had a couple of big volcanoes.
  2. We’re just coming off “the deepest solar minimum in nearly a century.”.
  3. The underlying long-term trend had been cooling (see Human-caused Arctic warming overtakes 2,000 years of natural cooling, “seminal” study finds, see figure below).

figure

The more important point is that the rapid increase in the human-driven component of the forcing are increasingly dwarfing the small, slow natural forcings, rendering them increasingly irrelevant (see “Humans boosting CO2 14,000 times faster than nature, overwhelming slow negative feedbacks“).  In the Anthropocene Epoch, humankind’s destiny is in its hands.

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23 Responses to Q: What percentage of global warming is due to human causes vs. natural causes?

  1. “How can humans be responsible for more than 100% of warming? Sounds like crack-pot alarmism to me.” That’s the response I’d expect Schmidt’s quote to draw. While it may be scientifically correct, saying that 120% of warming is due to humans is bound to raise some eyebrows – particularly with no further explanation at hand.

    [JR: I really would spend less time guessing what nonsensical disinformation the nonsensical disinformers will say. I think it's pretty straightforward that he's saying that absent some of the cooling trends (notably the solar forcing), we would have warmed more.]

  2. Mike says:

    What percent of ocean acidification is natural? 0%

  3. Scrooge says:

    This isn’t fair explaining it in such a clear and easily understood post. Still those that choose not to believe won’t let facts get in the way.

  4. What percentage of global warming are we willing to accept?

    What percentage of our legislation is based on irrational emotions and deluded thinking?

    What percentage of species extinction will we tolerate?

    What percentage of our current wealth are we willing to spend so that our children have a future?

  5. Wit's End says:

    What percentage of our children getting cancer from toxic fuel emissions are we willing to accept?

  6. catman306 says:

    Gaia will provide us with answers to richard pauli and Wit’s End’s questions. Our acceptance or rejection of these answers will have nothing to do with it.

  7. MapleLeaf says:

    But, but Curry says…Oh never mind– she thinks/believes that the certainty of warming in the surface data is only 70%!

    Meanwhile, we have this happening:

    http://www.skepticalscience.com/Greenland-ice-mass-loss-after-the-2010-summer.html#comments

  8. Solar Jim says:

    Clearly, the percentage the US Plutocracy is willing to accept is vast ecological collapse along with multi-trillion dollar redistribution of wealth to the rich, as well as government insolvency from fossil wars and dependency. These are truly burning questions.

    Is coal an “energy resource” or a solid?

    Is the US a house on FIRE (finance, insurance and real estate)?

    What percentage of the term “global warming” is meaningless to the public?

  9. Ric Steinberger says:

    The wealthiest Americans largely repudiate global climate change for two main reasons: 1) They have multiple houses in multiple locations, sometimes in different countries. They think there’s always someplace they can retreat to, if they have to. 2) They believe (correctly) that acknowledging global climate change means that the US government will have to act, and they assume, probably correctly, that this could well mean higher taxes for them.

    The largest US companies simply don’t want to face the possibility of any additional taxes, no matter what the reasons.

    The Tea Party types reject global warming for many reasons: 1) Rush Limbaugh tells them to. 2) They hate the idea that “liberal, elite scientists” are “behind” the idea. 3) Many of them believe in a Bible that assures them that “God” is in charge and wants them to “dominate” the earth. 4) they think (perhaps correctly in some cases) that accepting global warming means their jobs are threatened (e.g., coal miners), their taxes will go up (which could happen no matter what), and that “their” country is being taken over by “socialists”.

  10. Must comment on Catman306 “Gaia will provide us with answers … Our acceptance or rejection of these answers will have nothing to do with it.”

    We can accept answers, but we need not submit.

    Acceptance is not acquiescence.

  11. jcwinnie says:

    [Dee-Bluroop]sound effect and the screen reads GAME OVER

    http://www.huffingtonpost.com/2010/11/01/fate-of-the-world-climate_n_777094.html

    Do not attempt to insert more money in the machine. It will not matter.

  12. Robert says:

    The disinformers make a good target but it’s the apathy that’s the real killer. This is a Google Trands comparison of “climate change” vs. “football”:

    http://www.google.co.uk/trends?q=climate+change%2C+football&ctab=0&geo=all&date=all&sort=0

    Enter any trivial, transient item in place of “football” and you will find it is invariably of more interest to the sheeple than climate change.

  13. Geza Gyuk says:

    Heather Says:
    “How can humans be responsible for more than 100% of warming? Sounds like crack-pot alarmism to me.” That’s the response I’d expect Schmidt’s quote to draw. While it may be scientifically correct, saying that 120% of warming is due to humans is bound to raise some eyebrows – particularly with no further explanation at hand.

    [JR: I really would spend less time guessing what nonsensical disinformation the nonsensical disinformers will say. I think it's pretty straightforward that he's saying that absent some of the cooling trends (notably the solar forcing), we would have warmed more.]

    I don’t think Heather was talking about disinformers… I think she was talking about “the man on the street”. Not everyone who doesn’t believe in climate change is a disinformer, most are simply the “disinformed”!

    To physicists (myself included!) this way of speaking is fairly straightforward… but it isn’t necessarily so for people who aren’t used to it. If one is trying to overcome misinformation, then one has to know the audience one is talking to.

    Though, frankly I find it hard to see how anyone can take a look at the temperature graph and not immediately think “uh oh, we are in trouble…”, regardless of percentages or details. Which is why so much effort has been expended in trying to undermine it!

    [JR: I'd love it if the "man on the street" read this blog, but even if he did, I doubt it would be his response, and I'm quite sure it isn't the response of my actual readers.]

  14. Deborah Stark says:

    From Joe’s post:

    …..NASA’s Lacis: “There is no viable alternative to counteract global warming except through direct human effort to reduce the atmospheric CO2 level.”…..

    The climate research community has been concluding much of their literature with this warning for well over 20 years now. Also, the preponderance of think-tank documents (as far back as the 1970′s) on the matter of rapid pollution-driven climate destabilization concludes in one way or another that sustained “public pressure” will be absolutely necessary to push the kinds of changes we need to initiate if we are to leave the generations behind us with a livable planet. I started hard-copy archiving a lot of these documents in 1999 with the intent of passing the collection along to my son (now age 40) and his peers so that they will know how we ended up where we (they) are.

    Someone (thank you so much) posted a link yesterday on the Weekend Open Thread. The link leads to information about the iMatter March on Mother’s Day 2011. This global event will involve hundreds of thousands of children. Jim Hansen is supporting this event. Alec Loors, the young (age 16) activist from Ventura, California, is taking a leadership role in organizing it. Here is the link again:

    http://kvgw.org/

    I think this is going to be phenomenal.

  15. Leland Palmer says:

    Yes, of course we are responsible for most of it.

    But I was wondering about something else, this evening.

    Suppose that the climate/biosphere system seeks stability.

    Lovelock certainly thinks so.

    Is the decline in CO2 levels over the past tens of millions of years evidence that the climate system is finding stability at lower and lower levels of CO2?

    Astrophysicists tell us that according to the standard model of stellar evolution, the sun is a few percent hotter now than it was hundreds of millions of years ago. John Cook of Skeptical Science tells us this:

    Atmospheric CO2 levels have reached spectacular values in the deep past, possibly topping over 5000 ppm in the late Ordovician around 440 million years ago. However, solar activity also falls as you go further back. In the early Phanerozoic, solar output was about 4% less than current levels. The combined net effect from CO2 and solar variations are shown in Figure 2. Periods of geographically widespread ice are indicated by shaded areas.

    Periods of low CO2 coincide with periods of geographically widespread ice (with one notable exception, discussed below). This leads to the concept of the CO2-ice threshold – the CO2 level required to initiate a glaciation. When the sun is less active, the CO2-ice threshold is much higher. For example, while the CO2-ice threshold for present-day Earth is estimated to be 500 ppm, the equivalent threshold during the Late Ordovician (450 million years ago) is 3000 ppm.

    So, has the climate system been finding stability at lower and lower levels of CO2, due to the brighter sun?

    Apparently so.

    There is good carbon isotope ratio evidence of several massive releases of methane from hydrates in the past. The geologists talk about the End Permian, the Early Toracian, the Early Aptian, and the Paleocene/Eocene thermal maximum, as having very good evidence of several gigaton releases of methane from methane hydrates. The times assigned to these events are 250, 185, 120, and 50 million years ago, approximately. Estimates of carbon released during these events vary quite a bit but are typically several billion tons of methane. These methane releases seem to be associated as well with oceanic anoxic events and severe and rapid global warming.

    What I was wondering, though, is whether it will stop, this time. If we ignite runaway global warming, leading to a methane catastrophe, will it stop, this time?

    The sun is brighter, now, and our triggering CO2 increases are occurring faster- hundreds, even thousands of times faster.

  16. Mulga Mumblebrain says:

    jcwinnie,#13-I saw this computer game mentioned in a UK newspaper, -’The Guardian’,I think. The story contained a paragraph in the introduction that was not present in the main body of the story. It outlined a possible scenario where ‘you’, (the gamer/God) decide to create a virus to massively cull humanity, having decided, in your omniscience, that overpopulation was the root cause of ecological collapse.
    I was quite struck by just how carelessly such a genocidal and evil proposition had been included in the game’s make-up, and how it was reported without comment, as if it was just another possible course of action. Now, call me old-fashioned or a victim of ‘moral vanity’ (a common term of abuse in Australia, used by Rupert’s Moloch’s retinue of trained cane-toad propagandists, to refer to those with less evil inclinations than themselves)but I found this disgraceful and disturbing.Disgraceful because mass murder upsets my moral equilibrium, and disturbing because I keep seeing references to ‘over-population’ coming from the Right and some ersatz ‘Left environmentalists’, depicted as the root cause of all our woes, and I can’t help thinking that we are being softened-up for something very nasty.

  17. Harold Pierce Jr says:

    MM @18 says:

    “I keep seeing references to ‘over-population’ coming from the Right and some ersatz ‘Left environmentalists’, _depicted as the root cause of all our woes,_ and I can’t help thinking that we are being softened-up for something very nasty.”

    After studying a recent atlas of the earth I have concluded:

    1. There are few humans on the earth.

    2. Humans occupy are small portion of the earth’s surface.

    3. Humans have irreversible changed an even smaller portion of the earth’s surface by construction of cities and urban areas.

    4. About 50% of humans live in urban areas.

    5. Humans are migrating in ever increasing numbers from rural to urban areas, i.e., they are abandoning the countryside.

    A substantial fraction of the humans live in povery and consume little of the earth’s resources. Unfortunately they cause much enviromental damage by living off the land for food and resources suchas fire wood.
    Much of the flooding in Pakistan and China is due to deforestation.

    There are vast areas of the earth that are unpopulated by humans such as Siberia, Canada. Alaska, etc.

    The earth appears to be over populated because most televisions broad casts orginate in cities and urban areas. The earth seems small due to instant world wide communications systems in particular due to satellite TV.

    Humans have modified portions of the earth’s surface for agriculure. For example, much of the Great Plains have been modified for farming. Where there was once native grasses and wild animals, there are modified grasses such cereal grains and domesticsted animals.

    There are vast areas of earth that have been set aside as parks, recreational areas, and certain wilderness areas that are off limits to humans. Indeed, so much land has been set aside that an avid envromentalist could be on safari forever. So why are they still complaining and challenging every new human projects?

    Because they are low life wiseyguys who are running an enivormental protection racket, and they and their lawyers are shaking down goverments and companies for billions in out of court settlements. I recently read an article about this but forget to bookmark it.

    There is several ways to put end to these rackets. When they file a enviromental law suit, the judge could require them to produce evidence (i.e., a signed letter or form) that a majority of their members have approved the lawsuit. If they do win a law suit, the defendents should pay them off with pennies, nickels and dimes delivered to their office by a cement truck.

    A good example of this is the law suit they filed on behalf of delta smelt which they claimed was threatened by diverson of water from the Sacramento river for irrigation in the Cental Valley.

    The real reason is that the super rich city guys want the land for their country estates and hobby farms which they can buy for peanuts after the farmers go bust. This is “China Town” all over again.

    These guys should be charged with violation of the RICO laws. Who put up the money for the lawsuit: the rich silk-stocking enviros and limosine liberals (cf, A. Branch in L&O episode). If they do aquire the iand, the water will of course flow in abundance. Big swimming pools and horses need lots of water.

  18. Wit's End says:

    Deborah, I almost missed that all-important link! Thank you so much for posting it.

  19. David B. Benson says:

    Looking at the readily computer orbital forcing, one sees that it has been increasing for about 2000 years now. So it is possible that a small portion of the warming since the minimum during the LIA is due to changes in orbital elements, which redistribute the sun’s heat. I’ve made modest attempts to determine this and standard methods produce 0.06 K per century during the instrumental period (since 1`880 CE). That about 10% of the total and for other reason the value determined seems rather large. So I’ll say about 95% of the warming since 1880 CE is man-made.

  20. David B. Benson says:

    Other data suggests not more than 0.02 K per century warming due to change in orbital elements. So using 0.772 K as the warming over the past 100 years, at most 2.6% is presumably due to natural causes, leaving ~97% man-made.

  21. Leland Palmer says:

    One correction in my post number 17, for the record, although probably very few people are visiting this thread any more:

    I kept saying gigatons, or billions of tons of carbon. I should have been saying teratons, or trillions of tons of carbon. The isotope ratio spikes are fit best by several trillion tons of carbon from the methane hydrates, entering the atmosphere and oceans.

    This of course makes the problem worse, and runaway methane releases from the hydrates much more serious than the original post made these events sound. Sorry for the mistake.