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Updating the Climate Big Picture

Posted on 23 December 2011 by dana1981

When discussing climate science and looking at individual pieces of evidence and common myths, it's easy to lose sight of the forest for the trees.  That's why The Big Picture is one of the pages featured prominently on the Skeptical Science homepage.  However, we created that page over a year ago, so it's worthwhile to once again step back and take stock of what we know and what remains uncertain, and update the Big Picture.

The Earth is Warming

We know the planet is warming from surface temperature stations and satellites measuring the temperature of the Earth's surface and lower atmosphere. We also have various tools which have measured the warming of the Earth's oceans. Satellites have measured an energy imbalance at the top of the Earth's atmosphere. Glaciers, sea ice, and ice sheets are all receding. Sea levels are rising. Spring is arriving sooner each year.  There's simply no doubt - the planet is warming (Figure 1).

warming world

Figure 1: Indicators of a warming world

Global Warming Continues

And yes, the warming is continuing. The 2000s were hotter than the 1990s, which were hotter than the 1980s, which were hotter than the 1970s. 2010 tied for the hottest year on record.  The 12-month running average global temperature broke the record three times in 2010, according to NASA Goddard Institute for Space Studies (GISS) data.  Sea levels are still rising, ice is still receding, spring is still coming earlier, there's still a planetary energy imbalance, etc. etc.

Contrary to what some would like us to believe, the planet has not magically stopped warming.  Those who argue otherwise are confusing short-term noise with long-term global warming (Figure 2).

skeptics v realists v3

Figure 2: Berkeley Earth Surface Temperature (BEST) land-only surface temperature data (green) with linear trends applied to the timeframes 1973 to 1980, 1980 to 1988, 1988 to 1995, 1995 to 2001, 1998 to 2005, 2002 to 2010 (blue), and 1973 to 2010 (red).

Foster and Rahmstorf (2011) showed that when we filter out the short-term effects of the sun, volcanoes, and El Niño cycles, the underlying man-made global warming trend becomes even more clear (Figure 3).

before/after filtering

Figure 3: Temperature data (with a 12-month running average) before and after the short-term factor removal

For as much as atmospheric temperatures are rising, the amount of energy being absorbed by the planet is even more striking when one looks into the deep oceans  and the change in the global heat content (Figure 4).

heat content
Figure 4: Total global heat content. Data from Church et al 2011

Humans are Increasing Atmospheric Greenhouse Gases

The amount of greenhouse gases in the atmosphere - particularly carbon dioxide (CO2) - has been rising steadily over the past 150 years.  There are a number of lines of evidence which clearly demonstrate that this increase is due to human activities, primarily burning fossil fuels.

The most direct of evidence involves simple accounting. Humans are currently emitting approximately 30 billion tons of CO2 per year, and the amount in the atmosphere is increasing by about 15 billion tons per year.  Our emissions have to go somewhere - half goes into the atmosphere, while the other half is absorbed by the oceans (which is causing another major problem - ocean acidification). 

We also know the atmospheric increase is from burning fossil fuels because of the isotopic signature of the carbon in the atmosphere.  Carbon comes in three different isotopes, and plants have a preference for the lighter isotopes.  So if the fraction of lighter carbon isotopes in the atmosphere is increasing, we know the increase is due to burning plants and fossil fuels, and that is what scientists observe. 

The fact that humans are responsible for the increase in atmospheric CO2 is settled science.  The evidence is clear-cut.

Human Greenhouse Gases are Causing Global Warming

There is overwhelming evidence that humans are the dominant cause of the recent global warming, mainly due to our greenhouse gas emissions. Based on fundamental physics and math, we can quantify the amount of warming human activity is causing, and verify that we're responsible for essentially all of the global warming over the past 3 decades.  The aforementioned Foster and Rahmstorf (2011) found a 0.16°C per decade warming trend since 1979 after filtering out the short-term noise. 

In fact we expect human greenhouse gas emissions to cause more warming than we've thus far seen, due to the thermal inertia of the oceans (the time it takes to heat them).  Human aerosol emissions are also offsetting a significant amount of the warming by causing global dimming.  Huber and Knutti (2011) found that human greenhouse gas emissions have caused 66% more global warming  than has been observed since the 1950s, because the cooling effect of human aerosol emissions have offset about 44% of that warming.  They found that overall, human effects are responsible for approximately 100% of the observed global warming over the past 60 years (Figure 5).

knutti breakdown

Figure 5: Contributions of individual forcing agents to the total change in the decadal average temperature for three time periods. Error bars denote the 5–95% uncertainty range. The grey shading shows the estimated 5–95% range for internal variability based on the CMIP3 climate models. Observations are shown as dashed lines.

There are also numerous 'fingerprints' which we would expect to see from an increased greenhouse effect (i.e. more warming at night, at higher latitudes, upper atmosphere cooling) that we have indeed observed (Figure 6).

prints

Figure 6: Observed 'fingperprints' of man-made global warming

Climate models have projected the ensuing global warming to a high level of accuracy, verifying that we have a good understanding of the fundamental physics behind climate change.

Sometimes people ask "what would it take to falsify the man-made global warming theory?". Well, basically it would require that our fundamental understanding of physics be wrong, because that's what the theory is based on.  This fundamental physics has been scrutinized through scientific experiments for decades to centuries.

The Warming will Continue

We also know that if we continue to emit large amounts of greenhouse gases, the planet will continue to warm. We know that the climate sensitivity to a doubling of atmospheric CO2 from the pre-industrial level of 280 parts per million by volume (ppmv) to 560 ppmv (we're currently at 390 ppmv) will cause 2–4.5°C of warming. And we're headed for 560 ppmv in the mid-to-late 21st century if we continue business-as-usual emissions.

The precise sensitivity of the climate to increasing CO2 is still fairly uncertain: 2–4.5°C is a fairly wide range of likely values.  However, even if we're lucky and the climate sensitivity is just 2°C for doubled atmospheric CO2, if we continue on our current emissions path, we will commit ourselves to that amount of warming (2°C above pre-industrial levels) within the next 75 years.

The Net Result will be Bad

There will be some positive results of this continued warming. For example, an open Northwest Passage, enhanced growth for some plants and improved agriculture at high latitudes (though this will require use of more fertilizers), etc. However, the negatives will almost certainly outweigh the positives, by a long shot. We're talking decreased biodiversity, water shortages, increasing heat waves (both in frequency and intensity), decreased crop yields due to these impacts, damage to infrastructure, displacement of millions of people, etc.

Arguments to the contrary are superficial

One thing I've found in reading skeptic criticisms of climate science is that they're consistently superficial. For example, the criticisms of James Hansen's 1988 global warming projections never go beyond "he was wrong," when in reality it's important to evaluate what caused the discrepancy between his projections and actual climate changes, and what we can learn from this. And those who argue that "it's the Sun" fail to comprehend that we understand the major mechanisms by which the Sun influences the global climate, and that they cannot explain the current global warming trend. And those who argue "it's just a natural cycle" can never seem to identify exactly which natural cycle can explain the current warming, nor can they explain how our understanding of the fundamental climate physics is wrong.

There are legitimate unresolved questions

Much ado is made out of the expression "the science is settled."  The science is settled in terms of knowing that the planet is warming rapidly, and that humans are the dominant cause.

There are certainly unresolved issues.  As noted above, there's a big difference between a 2°C and a 4.5°C warming for a doubling of atmospheric CO2, and it's an important question to resolve, because we need to know how fast the planet will warm in order to know how fast we need to reduce our greenhouse gas emissions. There are significant uncertainties in some feedbacks which play into this question. For example, will clouds act as a net positive feedback (by trapping more heat, causing more warming) or negative feedback (by reflecting more sunlight, causing a cooling effect) as the planet continues to warm?  And exactly how much global warming is being offset by human aerosol emissions?

These are the sorts of questions we should be debating, and the issues that most climate scientists are investigating. Unfortunately there is a there is a very vocal contingent of people determined to continue arguing the resolved questions for which the science has already been settled. And when climate scientists are forced to respond to the constant propagation of misinformation on these settled issues, it just detracts from our investigation of the legitimate, unresolved, important questions.

Smart Risk Management Means Taking Action

People are usually very conservative when it comes to risk management.  Some of us buy fire insurance for our homes when the risk of a house fire is less than 1%, for example.  When it comes to important objects like cars and homes, we would rather be safe than sorry.

But there is arguably no more important object than the global climate.  We rely on the climate for our basic requirements, like having enough accessible food and water.  Prudent risk management in this case is clear.  The scientific evidence discussed above shows indisputably that there is a risk that we are headed towards very harmful climate change.  There are uncertainties as to how harmful the consequences will be, but uncertainty is not a valid reason for inaction.  There's very high uncertainty whether I'll ever be in a car accident, but it would be foolish of me not to prepare for that possibility by purchasing auto insurance.  Moreover, uncertainty cuts both ways, and it's just as likely that the consequences will be worse than we expect as it is that the consequences won't be very bad.

We Can Solve the Problem

The good news is that we have the tools we need to mitigate the risk posed by climate change.  A number of plans have been put forth to achieve the necessary greenhouse gas emissions cuts (i.e. here and here and here).  We already have all the technology we need.

Opponents often argue that mitigating global warming will hurt the economy, but the opposite is true.  Those who argue that reducing emissions will be too expensive ignore the costs of climate change - economic studies have consistently shown that mitigation is several times less costly than trying to adapt to climate change (Figure 7). 

Figure 7:  Approximate costs of climate action (green) and inaction (red) in 2100 and 2200. Sources: German Institute for Economic Research and Watkiss et al. 2005

This is why there is a consensus among economists with expertise in climate that we should put a price on carbon emissions (Figure 8).

should US reduce emissions

 

Figure 8: New York University survey results of economists with climate expertise when asked under what circumstances the USA should reduce its emissions

The Big Picture

The big picture is that we know the planet is warming, humans are causing it, there is a substantial risk to continuing on our current path, but we don't know exactly how large the risk is. However, uncertainty regarding the magnitude of the risk is not an excuse to ignore it. We also know that if we continue on a business-as-usual path, the risk of catastrophic consequences is very high.  In fact, the larger the uncertainty, the greater the potential for the exceptionally high risk scenario to become reality. We need to continue to decrease the uncertainty, but it's also critical to acknowledge what we know and what questions have been resolved, and that taking no action is not an option.  Th good news is that we know how to solve the problem, and that doing so will minimize the impact not only on the climate, but also on the economy.

The bottom line is that from every perspective - scientific, risk management, economic, etc. - there is no reason not to immeditately take serious action to mitigate climate change, and failing to do so would be exceptionally foolish.

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Comments

Comments 1 to 48:

  1. An excellent article that sums up the main points of the science. As the article says we need to concentrate on determining the feedback mechanisms so that we can provide a better understanding to the general public of what the future temperature increase will be. We know that a doubling of CO2 from 280ppm to 560ppm should produce a temperature increase of 2-4.5C. However, it's also clear that we don't currently have the 0.78C anomaly that the lower end of this range would predict for the 39% increase from 280ppm to 390ppm. The expected 5 year mean anomaly for 2011 is about 0.55 based on the annual figures and projected monthly figures from GISS http://data.giss.nasa.gov/gistemp/_graphs3/Fig.A2.txt
    I feel we need a more convincing strategy than to label our opponents as skeptics or denialists who don't understand the science. We should concentrate on the science rather than getting in to arguments which could be construed as overly defensive.
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  2. mace, we do already have the warming expected from the lower end of the range of climate sensitivities.

    Your link indicates that the surface temperature anomaly in the 1880s was -0.25 - -0.3 oC when [CO2] was ~293 ppm. The anomaly in your record is now 0.55 oC. So the warming is 0.8 - 0.85 oC over that period from your data.

    A 2 oC climate sensitivity should give an equilibrium warming of ~0.85 oC on raising [CO2] from 293 ppm then to 394 ppm now. So we've had pretty much all the warming already that is expected from the lower end climate sensitivity of 2 oC. Since the bulk of that warming has come from hugely enhanced increase in rate of [CO2] since the 1970's (i.e. relatively recently) we've got quite a bit of warming still to come as the Earth surface tends towards equilbration with the enhanced forcing.

    And that amount of warming has accrued despite the rather significant cooling contribution from greatly enhanced release of manmade atmospheric aerosols. Since the evidence indicates that natural warming contributions over this period (largely solar) have been small, this rather large temperature rise is in itself indicative that climate sensitivity is more likely nearer the middle of the range (i.e. near 3oC for a forcing equivalent to 2 x [CO2]) than the lower end.

    (one should also factor in the contribution to warming from other greenhouse gaes including methane, nitrous oxide, tropospheric ozone and CFC's....)
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  3. mace @1 - see has Earth warmed as much as expected? (short answer - yes it has).
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  4. Thanks both. Sorry, I get confused with the baselines for these anomalies from time to time.

    I've come across this which plots CO2 against temperature for the last 50 years which I think is pretty conclusive.

    http://www.geocraft.com/WVFossils/last_500_yrs.html
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    Response:

    [DB] As Rob says below, it is better to relay on actual source material rather than just some blog.  Data from the primary sources, placed in context, shows clear relationships between CO2 & temps difffering from the portrayals of your source:

    Click to enlarge

    Click to enlarge

  5. Mace - your confusion will not be alleviated by reading fake-skeptic blogs, like the one you just linked to. Peer-reviewed scientific literature is what you should be reading.
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  6. I think the scientific understanding of carbon-cycle feedbacks has reached a point where it warrants a line or two in "the big picture." Significant, ongoing releases of CO2 and methane from melting permafrost imply that, at best, emissions must be cut more aggressively than previously estimated to stop the rise in atmospheric CO2. At worst, it could mean that we initiate a process in which even a completely carbon-neutral society sees CO2 levels continue to rise for centuries.

    Without wishing to distract attention from the central problem of human emissions, I think carbon cycle feedbacks are important enough to be included in a review like this one.
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  7. Sorry guys, I think this one's the one I meant to post:-

    CO2 v Temperature over last 50K years *Blush*
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    Response:

    [DB] Rather than promulgating fake-skeptic graphs from dubious blogs, use rather the scientific sites, like this one from NASA:

    http://climate.nasa.gov/evidence/

  8. I think what's clear is that mother earth's been around billions of years, and we need at least 50,000 years to see the signal emerge from the climate noise. I think those ice core charts are a brilliant attack against deniers when they claim a few not so hot years are the sign of a cooling trend.
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    Response:

    [DB] "we need at least 50,000 years to see the signal emerge from the climate noise"

    Um, no.  That is the entire point of the Foster and Rahmstorf Measure the Global Warming Signal thread.  A thread which you have already commented upon..

  9. 4, mace,

    That's a wonderful find!!!! You should now look and see how the site you posted absolutely, undeniably and maliciously tricked you and anyone else who visits it.

    Concerning the "modern temperature record" they used, the recent temps (1979-2001) are supposedly from "Satellite stratospheric data," but since stratospheric temperatures (a) are not in any way indicative of surface temperatures and (b) have been cooling for the last 30 years (in accordance with GHG theory expectations), I think they really meant "tropospheric temperatures."

    Beyond this, however, if you compare the different measures, you'll find that comparing ground temperatures to tropospheric temperatures is apples and oranges.

    Concerning the temperature data from 1871 to 1979, why in the world did they use Southern Hemisphere data, of all possible global data sources? One has to scratch one's head at that choice. They may argue that it is similar to the Vostok ice core data (by at least being in the same hemisphere), but that sort of points out how wrong it is to compare any of that to the global mean satellite data.

    Concerning the temperature data from 1871 back... the temperatures at the poles change substantially more than the global mean temperature. This was true then and it's true now. It's called polar amplification.

    But the temperature swing in the Vostok data before 1871 is less than 2 degrees from the mean. The temperature swing today at the South Pole is more than 3. At the North Pole it's more than 4.5.

    So... they used three wildly disparate sources that show entirely different things that can't be compared, in particular a comparison of temperatures at one specific, extreme location in the past (one everyone knows will show more variation) as compared to the global mean temperature in the present (using a metric that everyone knows will show less variation in comparison, and yet it is by far the more important and more sensitive number).

    Quite a wonderful load of denial misrepresentation you've found!

    And let it be a lesson to you. Look into the data, and understand what you are looking at, before you accept what they are trying to sell you.
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  10. "I think what's clear is that mother earth's been around billions of years, and we need at least 50,000 years to see the signal emerge from the climate noise."

    Nope.

    The temperature signal shows two things:
    1/ internal variability (eg ENSO) which is unforced variation due to distributing heat around a water-covered planet. 30 years appears to more than enough time to account for this.

    2/ forced variability from natural forcings (eg sun (milankovitch and solar output variation), volcanic aerosols; and longer time scales - variation from continent arrangement and GHG variation due to biochemical factors.

    To claim that you need a longer time to sort natural from anthropogenic would require some evidence that there is natural variation that is not yet linked to a natural forcing. As it stands - no evidence that I am aware of. We can account for past variation from past forcings and we know the strength of current forcings. Natural forcing alone do not account for current climate (eg Meehl 2005 or the summary in the IPCC report).

    Furthermore, there needs to some magic that counteract the effect of the known physics of GHGs. So far the modelled effect of increased GHG is being reflected the observations. Ignoring that and praying for some natural variation fairy to let us off the hook is imprudent to me.
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  11. mace,
    The geocraft CO2 history has been debunked many times. See this CO2 was higher in the past thread.

    Once again, the best advice is to read and learn, rather than make decisions from unsubstantiated claims.
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  12. This is a great article. Just one niggle. Would you consider replacing the term 'conclusively prove' (in the Humans are Increasing Atmospheric Greenhouse Gases section) with something else? Lots of the non-scientists who resd this will interpret that as implying 100% certainty, and seeing the term used here makes them susceptible to the skeptics demand that they shouldn't believe anything unless it's 'proven'.
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  13. GrahamC, the term 'conclusively prove' appears nowhere in the above article.
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  14. Mr mace:

    You should be careful with the sources of information you use.
    Your source is called "Plant Fossils from West Virginia" (http://www.geocraft.com/WVFossils/Articles1.html)

    This innocent-looking site do not just question the science of global warming.

    It also has this section:
    "America has the Worlds Largest Coal Supply"

    where, in a few words, the following is sustained:

    1:America is the "Saudi Arabia" of Coal

    2:The Petroleum Dilemma

    3:Coal is the Key to Affordable Energy

    4:China Chooses Coal

    5:Renewable Energy Requires Coal

    6:Liquid Fuels from Coal

    7:U.S. Economy at a Crossroads

    It a series of half-truths that fall in one category of writing: propaganda.

    This shows that whoever wrote this page is on the side of the most dirty fossil fuel industry: coal. Obviously this is not a reliable source.
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  15. To show how even more unreliable is your source, I show how the piece I linked before ends:

    "U.S. Economy at a Crossroads: Ironically, the communist nation of China is making energy decisions based on capitalist principles , while the United States of America is floundering with a non-energy policy that most closely resembles a variation of European Socialism ."

    This page has also the following intro:

    "This page contains facts and figures about U.S. coal resources that every American should know.

    If you dislike America or capitalism you should not read this page. Go instead to this page: http://www.greensocialist.org.uk/ags/" (a british socialist page called Alliance for Green Socialism)

    This statements that want to accuse proponents of action against climate change of being politically biased towards socialism and communism are likely an example of projection: a trasfer the sub-conscient sense of guilt to your adversary.

    (-Snip-)
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    Response:

    [DB] Please refrain from remarks about politics and ideology (snipped).

  16. A quick question. Looking at sea levels from 2010 to 2011 shows a drop of ~8mm. Assuming that all this water ends up on land at an average elevation of ~5m gives this water a raise in potential energy of ~ 10^17 Joules. This energy will be converted back to heat as the water returns to the sea.

    Is 10^20 Joules a significant amount of energy in the atmosphere - upper ocean system?
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  17. Sorry - 10^17 Joules, not 10^20.
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  18. Believe me, Daniel Bailey, it was there in the original post.
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    Response:

    [dana1981] Oh yeah sorry, I just went ahead and made the suggested change.  Probably should have made a note - it's been a busy day.

  19. John Brookes @17 & 18, globally averaged it is 6 *10^-6 W/m^2, so no. Specifically with regard to ocean heat content, that measured in units of 10^22 Joules for convenience for the upper 700 meters.
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  20. At the risk of being off-topic here goes on big picture:

    - CO2 cumulates and incremental emissions have an atmospheric life of tens thousands of years [This is so if one assumes the sinks are cleaning up CO2 from many decades ago - the right way to look at it given the impending feedbacks].

    - The general public and most politicians thinks CO2 is a smelly Fart that dissipates quickly once we reduce CO2 emissions. Governments are not interested in informing them otherwise.

    - Nevertheless this means paleoclimate comparisons are valid given CO2 is the main driver of global temperature for a constant solar irradiance. However, given that the rate of CO2 increase is now 10,000 times quicker than in paleoclimate Newton would not hesitate to claim the transition to Pliocene paleoclimate conditions will also be much much quicker. Basically 25m sea level rises for the 2C target and lots of other nasties.

    http://www.giss.nasa.gov/research/news/20111208/
    http://www.youtube.com/watch?v=hK8BbOnvGJU

    - This wonderful website of yours gets 2 to 3 thousand users a day in a world of 7bn. It has done great work and is a fantastic resource.

    - But how can we change the understanding of the public to motivate the politicians ?

    Or is this off topic ? Best wishes.
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  21. Michael - the figure is around 20,000 visits per day IIRC. And no where near 7 billion people have access to the internet. Billions are currently starving, so blogging is way down the list of their priorities.
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  22. Thank you Rob
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  23. The choice of graphs seem a little questionable. BEST for example is a much poorer source of land data than NASA. Both have known bias but NASA has a lot more external people pulling the data apart and correcting their mistakes. This is likely to produce more accurate data. But more importantly: NASA produces more scientifically defensible data.

    This article really isn't going to convince *anyone* skeptical of the science behind Global Warming of *anything*. It also makes so many claims that it difficult to even discuss the science behind it. Can we get back to discussing science?

    If you want to convince a Global Warming skeptic that is the way. Sweeping science away in "the Big Picture" is what makes people skeptical of Global Warming theory in the first place.
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  24. iPCC use the phrase 'very likely' rather than settled. We should stick to the consensus view. Mankind adding gases to the atmosphere that cannot be naturally balanced is settled, but the link between this and global warming is 'very likely', rather than settled. Terminology is important.
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  25. JamesWilson#23:

    Your objections to BEST make no sense; that data set was gone over with a fine-toothed comb. See the several existing BEST data threads. What NASA data are you referring to as 'more scientifically defensible' and how does this differ from BEST? Please be sure to cite your sources for these assertions; this is science we're talking about, not hearsay.

    In case you hadn't noticed, there are hundreds of posts here discussing specific aspects of science. No one is 'sweeping science away.' Many people think having one 'big picture' thread is a very good idea. If you are looking to discuss a specific point, find the thread that deals with it - and read the posting.
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  26. JamesWilson - "Can we get back to discussing science?"

    Yes, indeed. Like for instance who is taking the NASA dating apart and correcting mistakes?

    " If you want to convince a Global Warming skeptic"

    SkS does not attempt to convince fake-skeptics. The evidence for man-made global warming is overwhelming, and yet they still resist the evidence, throwing up one illogical objection after the other.Trying to convince those people is a futile exercise.

    Our objective is right at the top of the home page: Explaining climate change science & rebutting global warming misinformation
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  27. This is an excellent piece of work, thanks. It is probably the most important information that this site puts out because it will do most to convince those who are confused by the opposing views that they are presented with in the media, yet becoming sufficiently worried about it to seek better information.

    On a technical note, I would like to see more emphasis on the projected sea level rise and its likely non-linear progression (re. Hanson and Sato). For instance, the U.K. government in its infinite wisdom is spending an absolute fortune, which it can ill afford, on the Olympic Games in a city that is vulnerable to sea level rise. The time will likely come in the not too distant future when the chosen site for the games will only be suitable for water-sports, which will, of course, work wonders for real estate values. Long before then, Canute like, there will need to be a new Thames Barrier unless they, the powers that be, wake up and take London to high ground, which won’t be cheap! (And they think that the current financial situation is bad.) It is amusing to read current plans for a new London airport in the Thames estuary, which, I assume, will be designed to accommodate modern versions of Sunderland and Catalina flying boats. Virtually all coastal cities are vulnerable in their own way. A potential three meter rise in sea level from the collapse of the West Antarctic Ice Sheet should concentrate the minds of many, especially of those that can’t swim.

    On a practical note, errors in proof reading will, in the minds of some, reflect errors in the science it discusses, which is a pity, considering the effort that has clearly gone into compiling it. Though having done some proof reading on my own publications, you have my deepest sympathy. I found the following:

    ‘theory?". Well’

    ‘Unfortunately there is a there is a very vocal’

    ‘Th good news’

    ‘not to immeditately take’
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  28. mace @24, you need to quote the section of the main article which calls something settled science and the equivalent claim from the IPCC which is called "very likely" (>90% likelihood). Otherwise your sentence is post is meaningless. As it stands I cannot find anything called "settled science" above which the IPCC only calls "very likely".
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  29. James Wilson, the strange assertions that you make must be supported, otherwise it's just trash talk about the work of others. What does "scientifically defensible" mean? Who are these "external people" and what have they published in the litterature? What are the "known biases"? In what papers were these biases analyzed? When I say papers, I mean peer-reviewed science papers from serious journals.

    You talk about getting back to the science but you don't provide any scientific reference to a lenghty set of wild assertions.

    If you decide to respond with anyting specific, make sure it is on an appropriate thread.
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  30. James Wilson, setting aside the points others have made about the lack of factual grounding in your comments... it needs to be pointed out that NASA temperature data is virtually identical to the BEST data. Frankly, your insinuation of 'questionable' data is nonsensical given that BEST was used because it is a 'skeptic' data set. Feel free to use NASA data instead. The results don't change.

    mace, in addition to Tom's points, you should realize that, "the link between this [humans increasing greenhouse gas concentrations] and global warming" is basic physics, and thus somewhat more than just 'very likely'. If the quantity of greenhouse gases goes up then the greenhouse effect increases (i.e. more IR radiation is retained in the atmosphere) and you have global warming. The only people who dispute that are crackpots and those who have been misled by crackpots. All of the prominent 'skeptic' scientists (e.g. Pielke, Spencer, Christy, Plimer, et cetera) concede that human greenhouse gas emissions are causing global warming.
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  31. @Tom Curtis, I'd be very worried if anybody on here wasn't completely familiar with the IPCC 4th report, which is the basis on which our concensus holds.

    The IPCC 4th report uses the following strictly defined terms:-
    'unequivical' i.e. 100% confidence
    'very likely' i.e. >90% confidence
    'likely' i.e >60% confidence.

    The phrase 'settled science' isn't used but could be construed in most people's minds to be closer to 'unequivical' than to 'very likely', whereas they are a long way apart.

    The IPCC report says the following:-
    1. That there has been a warming trend since 1978 is 'unequivical'
    2. That mankind is responsible for the increase in the percentage of greenhouse gases resident in the atmosphere is 'unequivical'
    3. That greenhouse gases trap heat is 'unequivical'
    4. That items 1 and 3 are directly linked to item 2, is 'very likely'.

    We need to carry on focussing on making the link in item 4, but claiming that this link is 'settled science' means that we have a complete understanding of the climate, which isn't yet the case. We need to continue the work so far, so that we can turn 'very likely' in to 'unequivical' and finally silence the skeptic-deniers.
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  32. mace if

    2. That mankind is responsible for the increase in the percentage of greenhouse gases resident in the atmosphere is 'unequivical'

    and

    3. That greenhouse gases trap heat is 'unequivical'

    How can the direct link between 2 and 3 be anything other than "unequivocal"? GHGs are GHGs whether they are due to anthopogenic emissions or not.

    Furthermore you do not appear to understand the link between 2/3 and 1. If it is unequivocal that anthropogenic emissions are increasing the amount of GHGs in the atmopshere and that it is unequivocal that GHGs trap heat, then it follows that it is unequivocal that all things being otherwise equal we are causing the Earth to warm. The only uncertainties lie in changes in other forcings and unforced climate variability. The uncertainty due to the former is fairly small; the variability of the latter is enough that scientific honesty means that we should not claim that the rise actually observed can be unequivocally attributed to our emissions.

    None of this is a rational reason for skeptics to doubt that our emissions are afecting the climate, and suggesting that an unequivocal link should be required to silence the skeptics is deeply misguided. The deniers will accept any uncertainty to support their view, no matter how small. The correct argument to make is that there can be no absolute proof of a causal relationship regarding the real world based on observational or experimental evidence.

    PLEASE can you read more widely before posting, you are still contributing to the noise rater than the signal.
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  33. @Dikran Marsupial. The reason why the IPCC does not make the link, as you reckon they should, is because we need to unequivically prove that the amount of greenhouse gas produced by man and not re-absorbed in the carbon cycle, is responsible for global warming. At the moment, it's 'very likely', but to move it to be unequivical will, unfortunately, take a lot more proof. The problem that we have is that the climate is obviously very complex, and the interaction between natural and manmade forcing agents and other feedback mechanisms isn't wholly understood.

    The problem with claiming that we have 'unequivical' proof that the link is made, is that this would mean that the public would expect us to be able to reliably predict the global mean temperature within a short time frame, 5 years, say, to a degree of accuracy comparable to what they expect from other unequivically proven scientific theories. I would expect that with each report publication, our degree of confidence will be raised each time, which will increasingly move public opinion in our direction.
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  34. The direct link to the relevant section in the IPCC report is here:-
    http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9s9-7.html
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  35. "suggesting that an unequivocal link should be required to silence the skeptics is deeply misguided. The deniers will accept any uncertainty to support their view, no matter how small"

    True, but there are still people that deny the existence of dinosaurs, for example. Our aim isn't to eliminate all deniers but to marginalise them by producing more and more evidence to support anthropogenic causes of global warming.
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  36. This might be off topic (in which case I can repost on any other suggested thread), but as others have brought up the subject...

    With reference to the use of the phrase 'climate skeptic' (or 'sceptic' if, like me, you're British): I read someone the other day using the phrase 'climate cynic' (I think it was Joe Romm). I must say I much prefer that to the phrase 'fake sceptic'. My reason being that, OK, we know what 'fake sceptic' means, but to a lay-person it needs explanation.

    As we all agree, to be sceptical of evidence or ideas that appear to contradict accepted science is a good thing; consequently I don't feel it's right give validity to the word 'sceptic' in the context of a person who is ideologically opposed to the concept of man-made warming. Also, given the way in some quarters use of the word, 'denier' is being manipulated to suggest ideological abuse of 'climate cynics', then maybe this new phrase should be run up the mast and given an airing?
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  37. mace wrote "True, but there are still people that deny the existence of dinosaurs, for example. Our aim isn't to eliminate all deniers but to marginalise them by producing more and more evidence to support anthropogenic causes of global warming."

    You have just contradicted your earlier post. No amount o evidence supporting anthropogenic causes of global warming will ever make the trend 1978-present unequivocal, for the reasons I gave.

    The way to marginalise the skeptics (like those who doubt the existence of dinosaurs) is not to add evidence, but to show that absolute proof is fundamentally impossible, as good scientists know. This requiring unqeuivocal proof is irrational and unreasonable.

    What you have done is suggest that this requirement for an unequivocal link is somehow reasonable, and hence playing into the hands of the "skeptics" rather than marginalising them. This issue has been discussed more than once on SkS, so I repeat my advice, please read more before posting.
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  38. @Dikran Marsupial. Fair point. In my previous post, I should have said we need to move from 'very likely' towards 'unequivocal'. From the table in the IPCC link, you can see that there a lot of areas in which we will be able to move from 'More likely than not', 'Likely', 'Very Likely' and 'Extremely Likely (>95%)' to unequivocal i.e. 100%. In the 5th report, I would expect most of the current gradings to increase in their levels of confidence.

    I liken our current predicament with that of early cancer scientists. However, we need to keep an open mind ourselves. In 1926, Johannes Fibiger received the nobel prize for medicine for his discovery that a microscopic worm caused stomach cancer in rats, from which he deduced this was a possible cause in humans. http://www.nndb.com/people/172/000126791/
    This is why it's dangerous to label things which are 'very likely' as 'settled science'.
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  39. mace You are merely repeating your error. That anthropogenic emissions of GHG will raise global temperatures, all things being otherwise equal is already unequivocal. However that doens't mean that the warming since 1978 can be unequivocally attributed at anthropogenic emissions because of the "all things being equal" part. The doubt isn't due to the link between GHGs and radative forcing or climate sensitivity. It is because of uncertainties in observations of other forcings and internal climate variability. As I said that is no reason to doubt the link between anthropogenic emissions and global warming. Until you understand that point, repeating weakened versions of your original statement is merely contributing to the noise, not the signal.

    Some of the science IS settled. Some is not. The attribution of the observed warming since 1978 to anthropogenic causes is not completely settled, for the reasons I have given.

    It is a bit like attributing a particular extreme climate event to global warming, we can't really do this, we can only say that "all things being otherwise equal" a rise in global temperature will make those extremes more common or worse. Does that mean we don't need to worry about global temperatures with respect to extreme events? No, of course not.

    We don't need to move the evidence anywhere; the evidence is what it is. What we need to do is to act rationally on the evidence that we do have. If someone told you that crossing a busy street with your eye closed is "very likely" that you will be run over by a truck. Is that enough for you to keep your eyes open when crossing the street, or do you need to be told that it is "unequivocal" that you would be run over? The "skeptics" are in the latter position.
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  40. @Dikran Marsupial. I think we're in agreement here. If I was told it's 'very likely' that if I cross the road, I'll be knocked over by a bus, I'd be wary of crossing the road whenever I saw a bus. If I was told that it was 'unequivocal' that sticking my fingers in an electrical socket will at the very least cause burns and potentially death, then I'd definitely not be sticking my fingers in the socket. So, there is a big difference between the 2 statements. My original point is that we need to be extremely careful in our use of language.
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  41. @Dikran #37.

    As I know you know, absolute proof is possible, given enough time for events to unfold. However if we want to avoid potential disaster we can't wait that long. The level of probability that climate cynics demand is way beyond what they would require for any other aspect of their lives.

    I ask them: if there was a 90% chance that the family house they lived in was going to collapse at some time in the next twenty years, would they demand more evidence, or would they get out, fast?

    If evidence suggested that there was a 90% chance that our planet was going to be hit by a large asteroid in 30 year's time unless we start work now on a solution; what would they say to me if I told them it was all a scam to raise tax? Moreover it was dreamt up by a conspiracy of scientists: and here's a scientist who used to be big before he retired in the 1990s who's published a paper that shows asteroids don't exist. Anyway, Earth has been hit by asteroids many times before without a problem. And asteroid dust is good for plants. And even if it's true that an asteroid is heading for us, don't to worry -- it'll probably miss us.

    In the face of so many lines of evidence for man-made climate change, as you say, requiring unequivocal proof is irrational and unreasonable.
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  42. mace@40 no, we are not in agreement. We can be sure that increasing atmospheric CO2 concentrations will increase temperatures without being sure that the observed warming since 1978 was caused by anthropogenic emissions. Thus your argument that we need to make this link unequivocal implies that a "skeptic" requirement for this linke to be unequivocal is somehow rational or reasonable. When you agree that this requirement is irrational and unreasonable, then we will be in agreement.
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  43. John Russell wrote "As I know you know, absolute proof is possible,"

    This is incorrect, I don't want this thread to descend into yet another discussion of the philisophy of science, David Hume showed that we can have no certain knowledge of causal relationships in the real world. Instead, as Hume suggests, we should apportion our belief according to the evidence, but this falls well short of "absolute proof".

    The point is that the original statement referred to a warming trend since 1978. One could argue that the warming we have observed is due to deep ocean currents redistributing heat within the climate system. Our knowledge of deep ocean currents in the 1980s is unlikely to improve much on what we already know as we don't have a time machine to go back and take more measurements. Thus there will always be irreducible uncertainty on the attribution of warming over that period.

    What mace fails to understand is that there is a difference between what we can say "all things being otherwise equal" and what we can say about specific observed events.
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  44. Dikran Marsupial & John Russell:

    Re your exchanges with mace, "Beware of a wolf in sheep's clothing."
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    Moderator Response: [muoncounter] Let's go a step further. This posting is a summary article, not a detailed analysis. Protracted argument over exact wording is a distraction; let's make further commentary over shades of meaning of terms like 'very likely' off-topic from this point forward.
    If you would like to continue detailed discussion of specific terminology in IPCC AR4, there are several topic-specific IPCC threads.
  45. #41 John Russell : "I ask them: if there was a 90% chance that the family house they lived in was going to collapse at some time in the next twenty years, would they demand more evidence, or would they get out, fast? "

    For a skeptic mind, this is typically not a good metaphor or analogy (I've already had this kind of debate with Tom Curtis, by the way). I dislike analogies, but if you want absolutely use some, they must be convincing. In climate sciences' conclusions assessed by IPCC (which form the base for policy advice and citizen reflexion), the 90% level of confidence we're discussing does not concern a "collapse" in a short period (20 years), but an attribution (of past 60 years warming to GHGs as the main cause).

    See for example confidence levels in the latest IPCC report on extreme events, SREX 2011 (policymakers read the IPCC reports' SPM, not the full report and not some particular work in the abundant literature).
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    Response:

    [DB] As previously noted, IPCC discussion is OT here.  Please take this area of the discussion to the IPCC Reports: Science or Spin? thread.

  46. Sorry if I have misunderstood something, Dikran, but won't we have absolute proof of the consequence of our actions in 50/100 year's time, when we are experiencing the results of putting another ~200ppm of CO2 in the atmosphere? Or are you arguing that nothing can ever be 'absolute' proof?

    (I've also posted this comment on the 'IPCC Reports: Science or Spin' thread)

    [Moderator: by all means delete this post if it's O.T., but if you do, please delete my earlier post as well. Thanks.]
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  47. Dana:

    Figure 1: "Indicators of Warming" ought to be expanded to include severe dought/desertification and severe rainfall/flooding. These two indcators should be mentioned in the text as well.
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  48. Just to give a piece of context, the change in ocean heat content (joules) from 1960 to date is more that ten times the energy contained in the combined gas and petroleum reserves known in 2010.
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