One Hundred Years is not Enough

By illconsidered on January 25, 2006.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

Objection:

Global surface temperatures recorded over just one hundred and some years is not long enough to draw any conclusions or worry about anyway.

Answer:

The reliable instrumental record only goes back 150 years in the CRU analysis, 125 in the NASA analysis. This is a simple fact that we are stuck with. 2005 was the warmest year recorded in that period according to NASA, a very close second according to CRU. Because of this limit, it is not enough to say today that these are the warmest years since 150 years ago, rather one should say 'at least':

1998 and 2005 are the warmest two years in at least the last 150.

But there is another direct measurement record available that can tell us things about temperature over the last 500 years, and that is borehole measurements. Basically, this involves drilling a deep hole and measuring the temperature of the earth at various depths. This gives us information about century scale temperature trends as warmer or cooler pulses from long term surface changes propagate down through the crust. Using this method we can see that temperatures have not been consistently this high as far back as this method allows us to look. This way of inferring surface temperatures does smooth out yearly fluctuations and even short term trends, so we can not know anything directly about individual years. But given the observable range of inter-annual variations recorded over the last century, it is quite reasonable to rule out single years or even decades being far enough above the baseline to rival today.

Thus, using this record, we can extend our timeframe and reasonably conclude that it is warmer now than any time in at least the last 500 years.

It is possible to make reconstructions of temperature much further back, using what are called proxy data. These include things like tree rings, ocean sediment, coral growth, layers in stalagmites and others. The reconstructions available are all slightly different and provide sometimes more and sometimes less global versus regional coverage over the last one or two thousand years. Note: this covers the period often referred to as the Medieval Warm Period. As noted, all these reconstructions are different, but:

they all show some similar patterns of temperature change over the last several centuries. Most striking is the fact that each record reveals that the 20th century is the warmest of the entire record, and that warming was most dramatic after 1920

http://www.ncdc.noaa.gov/paleo/globalwarming/paleolast.html

Thus we can reasonably say it is warmer now than any other time in at least the last one thousand years.

The only other candidate for a higher temperature period going back through the entire Holocene (~10,000bp to now) is called the Holocene Climatic Optimum some 6000 years ago. It is not known exactly what the temperatures were then, the farther back in time we try to look, the greater the uncertainties there are to deal with. Even so, the Holocene Climatic Optimum has long been cautiously thought to be almost as warm or even warmer than now. That conclusion is starting to look less likely as it has been determined that the anomalous warmth of that time was actually confined to the northern hemisphere and occurred only in the summer months.

Robert Rohde's website, Global Warming Art has a nice graph of many reconstructions of Holocene temperature, regional and global, all super-imposed with an average of all of them combined, shown below. This represents the best estimate available of global temperatures in the Holocene.

Thus one can reasonably believe that it is warmer now than at any other time in at least the last 10,000 years.

Before the current interglacial the planet was in the grip of a much colder glacial period with ice sheets well down into the continental US. This period only just ended some 11,000 years ago. The record of glacial-interglacial cycles can be read in Antarctic ice core analysis and it shows these cycles over many 100Kyr periods. The IPCC offers a good version of this graph.

Thus we can say that if our reading of the Holocene is correct, it is warmer now than at any other time in over the last 100,000 years.

And that is a bit more than 100 years. It is in fact the entire history of our species.

This is just one of dozens of responses to common climate change denial arguments, which can all be found at How to Talk to a Climate Sceptic.

"One Hundred Years is not Enough" was first published here, where you can still find the original comment thread. This updated version is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.

More like this

I've always found that a good response to this is "well, how many years is enough?" they very rarely have a good response.

It is a Statistical fact that no amount of years is enough to prove both cases. (Global Warming vs No Global Warming)

(1) Does anyone have a hypothesis about the temperature spikes 120,000 and 230,000 and 320,000 years ago? How credible is the ice data to support these observations?

[coby says:
The glacial cycles are caused by Milankovich cycles, that is these orbital variations change the distribution of sunlight on earth's surface. The ice core data is very rich and very robust and the swings in temp and atmospheric composition agree with ocean sediment records.]

(2) The ice data suggest the current temperature spike began over 10,000 years ago, and was essentially complete 3000 years ago. The 10 degree warming of that spike dwarfs the 0.8 degree warming shown by the NASA/CRU data. Why do you think your data rebuts the "objection" you pose at the top of the page?

[coby:
The objection is about how significant the recent record high temperatures are. This data shows that it has been an extremely long time since the earth saw global average temperatures like today's. I have other articles about the causes and character of those temperature changes, please see those.]

(3) It will be interesting to see whether reduced emissions due to the current recession have a meaningful impact. Your data shows that World War II had a clear impact on global temperatures, but this drastic change in human activity only produced an impact of 0.25 degrees. What is our real opportunity to affect climate by incremental changes in social behavior?

(4) Of the myriad insults humans have given the planet, why have you singled out CO2 as a single source of problems? For example, you mention in your book that methane may have a much more powerful impact because its background level is low. Might we be causing more problems by wasting gas when drilling for oil that we cause with CO2? What else are we doing that needs attention?

[coby:
I talk about CO2 because it is the single largest factor in AGW. You are correct that there are many other important environmental issues out there, but the focus of this site is global warming]

Cody, you make this statement in the Co2 Lags article:

"The "junk" about being precise is the reality of the ice cores. The resolution is not annual when you go farther back in time. Some of the data points represent time periods thousands of years apart."

If this is resolution we have for past climate cycles, how can any meaningful comparison with the mere last 50yrs of well measured and recorded data be drawn?

I don't see how this works against the skeptic. I would think that the argument would go that temperatures have been rising steadily since 1700 (Pollack reconstruction for example). During much of that period CO2 levels were not rising from industrial output, so why attribute the last portion of the rise to CO2 output solely on this evidence.

Put in other terms don't we need to explain the rise from 1700 to about 1940, and then subtract that explanation from the rise from 1940 onward?

I note also that the Pollack reconstruction doesn't seem to have the same shape as the other proxy reconstruction during the overlapping periods.

Hi Nicolas,

Focusing on the Pollack reconstruction, we do not see a `steady rise` but rather an exponentially increasing one! There is no reason to try to base any theory soley on this one reconstruction.

As for the details of causes, no one who has put any thought into how the climate works thinks that CO2 is the one and only factor. The evidence currently indicate that the 1700-1900 rise was primarily solar driven as the world came out of the `Maunder minimum`. The early 20th century is a combination of solar, volcanic and GHG forcings. The late 20th century accelerating warming is being driven by anthropogenic changes to the environment, CO2, CH4, soot, land use. No significant solar or volcanic forcings are evident.

Thanks for the comment!

A thoughtful "skeptic" knows that CO2 is a positive forcing, but that the key is how the actual climate system reacts with various feedbacks. Theory since about 1980 has pretty solidly stayed with the idea that the various feedbacks plus the direct forcing of CO2 would cause a 1.5-4.5 degree C increase with doubling of CO2. But as I think everyone agrees this is still theory.

The question then becomes when does theory become fact (or as close as you can get in the physical sciences.)?

Someone looking at this specific post for evidence that the theory is correct won't find it. As I point out the Pollack curve shows steady increase over the period. You say it is exponential although it doesn't look like it to me, but the slope does appear to be increasing. The problem is that the increase in slope appears to start before significant introduction of CO2. The other reconstruction just looks like a bunch of averaged random squiggles until the instrumental period.

Arguments that the recent rise is particularly rapid are interesting, but I'm not sure that we actually know the pace of previous increases accurately enough to make that statement. It also starts getting us into exceedingly short time frames like 1980-2000 and silly arguments over whether the post 2000 period matters, or which measurement system is the most accurate.

The reality, it seems to me, is that the theory is very solid based on a lot of work, and many attempts to test it against paleo-climate etc. But there is as yet no proof that it is correct. Likewise there is certainly no proof that it is not correct.

"I think everyone agrees this is still theory."

Indeed, and it will always be a theory! But as more than just a pedantic point, I might add that in the case of sensitivity to CO2 we will never get the same confidence as we have with many other scientific "facts" (aka confident theories). The climate system is simply too large, slow and complex and there is no possibility of running real experiments, only model experiments.

This post is not trying to give a general argument about the AGW theory. I did give this a try here.

I agree that statements about how different today's change is from the past are only as strong as our confidence in proxy reconstructions, and this is quite low, especially on short time frames. I do however think that general understanding of the climate system can usefully constrain the range of possibilities for past global temperature trajectories enough to say it is really very likely that what we see today is not normal.

"The reality, it seems to me, is that the theory is very solid based on a lot of work, and many attempts to test it against paleo-climate etc. But there is as yet no proof that it is correct. Likewise there is certainly no proof that it is not correct."

I don't think any reasonable person can disagree with this!

Hi Eric,

you said"

"If this is resolution we have for past climate cycles, how can any meaningful comparison with the mere last 50yrs of well measured and recorded data be drawn?"

The comparisons are very limited, to be sure. The most useful aspect of this data is its use in generally testing models and specifically constraining climate sensitivity values.

Hi Thirsty,

I have replied to your recent comment inline.

Thanks for the visit.

Coby you said "I think everyone agrees this is still theory." True it is but a theory, if so why do its proponents talk as if the "science is in"? The planet is cooling not warming as C02 levels continue to rise, how many years of global cooling do we need to disprove the "theory"? Nicolas Nierenberg asked what caused the temp rise from 1700 to about 1940 if not C02, you dodged that bullit by saying there are "other factors" namely solar at work driving the climate. Okay lets all agree on that, so C02 is rising and temperatures are falling because of "other factors" solar?

In sumary 1700 to 1940 rise due to solar, 1940 to lets say 1998 caused by C02, 1998 to 2008 temp drop caused by what?

Coby Im sorry, but I am distinctly unimpressed by your post above. You say that the temperatures today are "very likely" not normal. Yet at the same time say this is "still theory" and that there is "no proof that it is correct". And how do these fit in with your statement below (and Ill quote the whole paragraph):

"But what certainty there is about the basic issue is close enough to 100% for all practical purposes that it should be taken as 100%. Don't wait any longer for scientific certainty, because we are there. Every major institute that deals with climate related science is saying AGW is here and real and dangerous, even though they will not remove the "very likely" and "strongly indicated" qualifiers. The translation of what the science is saying into the language of the public is this: Global warming is definitely happening and it is definitely because of human activities and it will definitely continue as long as CO2 keeps rising in the atmosphere."

http://scienceblogs.com/illconsidered/2006/04/scientists-arent-even-sur…

I dont see the phrases is "still theory" and "no proof that it is correct" there. It cant be both. It cant be both "certain" and "still a theory without any proof that its correct" can it? (And please think twice before repeating the Newtonian Mechanics Relativity argument from the post linked to above)

This is not the first time a lack of clarity has been so obvious.

http://scienceblogs.com/illconsidered/2006/04/models-dont-have-clouds.p…

Lets face the obvious - such verbal gymnastics are only required when one has to avoid having to state the plain truth.

The Halocene temperature plots and average plot of the various plots seems to me to highlight the shortness of the 20th century temperature rise as attributable to man. The borehole temperatures seems to indicate another driver than man, as it starts befor man got underway with real carbon freeing activities. How can this conclusion be reached based on these plots, "Thus one can reasonably believe that it is warmer now than at any other time in at least the last 10,000 years." The current high temps are not amenable to construning that ther is enough time in them to be place in the trend. In fact it seems to me that it is just as easilly said that they are consistent with the plot. Problem is that in the time scale the last 10 years is in fact the "particular" and cannot prove the general. We dont know if there were micro period of ups and downs at any time, with ups like, or more, than we have recently experienced.

Hi Matt,

It is quite true that due to poor temporal resolution these reconstructions alone can not rule out brief spikes and dips that could exceed anything observed recently. BUT, when combined with an understanding of what drives climate changes and the inertia of global response to forcings we can gain much more confidence in filling in the dots, so to speak.

There are no known mechanisms whereby the globally averaged temperature can jump up and down by degrees within such short timeframes and leave no trac of this in any proxy records.

Thanks for the comment!

Hi Coby, Thanks for the response. But you need to be more specific, I am trying to follow the science and logical arguments to support man caused heating of the earth. Lets take the Pollack Reconstruction. The curve's shape is consistent with the response of a system responding to a stimulus of some sort, but the stimulus starts long before man started to create CO2 and is persisting. The fluctuation about the curve look within a normal system's varibility about a fundamental underlying change. So how does this work support the man caused warming arguement? In fact it it appears to point to something else. Cheers Matt

If a child or a monkey scribbled with colored pencils it would probably make more sense than this assortment of convoluted data.

Shorter Harry:

These graphs don't line up with my preconceptions, so I will disregard the data with a snarky comment.

Matt-
The diagram which Coby posted is a schematic from here:

the actual data is usually plotted like this:
http://www.geo.lsa.umich.edu/climate/RECONSTRUCTION/CA-9105.html

Hi Coby,

You note above the 400k year graph that

"Thus we can say that if our reading of the Holocene is correct, it is warmer now than at any other time in over the last 100,000 years."

And you conclude...

"And that is a bit more than 100 years. It is in fact the entire history of our species."

OK, no doubt about that. But isn't the crux of the AGW argument not whether it is hotter now than at any time during the history of our species, but whether the present warming is anthropogenic, and, by extension, something we can (and should) be doing something about?

The graph shows that it has been much hotter than present around 125k years as well as 325k years ago. I'm not a climate change scientist, but when I look at that graph it seems difficult to argue that our present warming is in any way unusual, or anthropogenic, for that matter.

As a layperson it's impossible to come to a conclusion about who is right. And, as their are eminent scientists disagreeing on the subject, it appears to be the same even if you've invested an entire adult lifetime studying the subject. 'Warmists' all claim to have a 'consensus', 'deniers' poke what seem to be very large holes in their arguments, and most of the spokespeople for either movement appear to have vested interests in their positions. And meanwhile, the public are being readied to stump up colossal sums for things like sequestration, which, if the 'deniers' are right, will probably have no useful impact on our climate whatsoever - and prevent us doing other useful things.

Hi Big Jim,

Yes, you are quite right about what is the crux of the issue. This article is targeting one very specific talking point commonly used in the debate to discredit the conclusions of the IPCC reports. My goal with How to talk to a Sceptic was to go point by point, through over 60 arguments, and deal with each in turn. Pro/con AGW debates suffer from constant digressions and because of that quickly become unproductive. I am not aware of any "very large holes" deniers have been successful at poking.

For example, I deal with the point that it has been warmer before here and the suggestion that this is similar to other changes here.

For a brief overview of just why humans are being blamed for the current change, please see this post. For the whole story, you can not do better than reading the IPCC reports. Despite criticisms you might hear, they are based on the current state of peer reviewed research and have been reviewed by just about every scientific organisation with relevant expertise and found to be quite sound.

I disagree that for a lay person it is impossible to arrive at an intelligent conclusion, though it is clearly a lot of work especially considering the amount of deliberate misinformation that is out there. But if you (like most people!) have other things going on in your life you can and should trust the vast majority of climate experts out there. There are actually only a very few (perhaps 3 to 5) individuals who can truly claim to be eminent climatologists and do not fully endorse the major points of the consensus: 1. it is warming, 2. the cause is mostly anthropogenic, and 3. this represents a dangerous interference in the global climate.

Those individuals will only disagree on the last point. Maybe you have some specific people in mind?

Have a look at the research discussed here for further reassurance that the IPCC conclusion is extremely well founded and supported by the actual experts in the field.

Re: spending money, personally, I can not yet endorse money spent on sequestration or corn-based ethanol, but that is another discussion. Misguided political decisions don't help the PR case, but they are irrelevant to the scientific basis of climate change.

Thanks for your comment and questions!

You know it's nanoAl that has it right that most wouldn't know what to say if asked how many years is enough? So we need to pull in the skeptic in other ways >

I would start by explaining it was mans ingenuity which identified fossil fuels and how to extract and burn them to create energy that has brought us sustained improvement in expected life span and increased our standard of living and level of comfort beyond our wildest dreams.

The progress we have made over a mere 2-300 years is so phenomenal and the time freed up by our current level of productivity which is surely laid at the feet of fossil fuels will allow us to out engineer any possibly negative effects of the coming global warming.

I would also explain that the number of bright dedicated individuals and groups who inform us about global warming will lead us in the right direction. You will be able to tell how soon it is until the impending doom of civilization by their increased activity turning off lights, selling off cars and airplanes, etc. basically doing anything to lower their carbon foot print to nothing because of the extreme urgency of the situation.

So there you have it, bright industrious worker types working on the long range plan, solving problems as they occur. And the "canarys in the mine" so to speak, becoming ever more visible exemplifying how to live "sustainably" if the end draws near and the rest don't see it!

This is a curious temperature chart..

XXXX://www.globalwarmingart.com/wiki/Image:Phanerozoic_Climate_Change_Rev_png

It actually appears that the earth in in the midst of a global cold period... what the heck is the best termperature for the earth?

Hi catman2,

See the answer to your other comment posing a similar question. The short answer is the best climate is the one the earth's life forms are adapted to.

Hi Cody,

Can you help me address claims made here (http://alexhorovitz.com/blog/2009/05/how-i-learned-to-stop-worrying-abo…) that our time horizon should be in the hundreds of millions of years. And the additional claim, based on the model put forth in the referenced paper, that there is no correlation, let alone causation, between co2 levels and global temperature.

thanks.

I find it amazing that NASA was doing accurate measurement 125 years ago! As someone who has a minor in meteorology and has been following the global warming situation since the 70's I am stunned by the amount of information that has been been changed or disappeared off the Internet. I am so grateful that I have my original notes,printouts from National Weather collecting centers, and books to remind myself that I have not lost my mind but that someone is trying to make money off something they still are not sure about.

I will not list all the blatant lies. Well, other than the first one about NASA.

Are you even aware of when the first Landsat was launched? Where and who did the first weather collecting data? And just how it was done?

Have you ever heard of "gaps" in the geologic time table? It they can happen in rock, just imagine how easily they can happen in ice. And just what does ICE tell us about CO2 in the air? Where is the year of Krakatoa? I imagine New Yorkers would have something to say about that if they were alive today.

Hi Mollie,

Thanks for a rather bizarre mix of paranoia, incoherence and non sequiturs. If you have any sincerity in your queries, please read the IPCC reports. http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

Start at the summary and chapter introductions and continue as your inquisitiveness dicates.

I am stunned by the amount of information that has been been changed or disappeared off the Internet. I am so grateful that I have my original notes,printouts from National Weather collecting centers, and books to remind myself that I have not lost my mind but that someone is trying to make money off something they still are not sure about.

Great, then you'll have no problem stating one example of information that was once on the internet, and has now been removed, right?

You'll be able to use the "wayback machine" project to prove your point, right?

Put up or shut up.

The Climategate
scandal sheds a whole new light on this.

Have you ever heard of scientists (other than Pons
& Fleishman) keeping their raw data secret after they published, to
prevent other scientists from critiquing and verifying their results?Â