THEGREENGROK

Global Warming and Predictions of an Impending Ice Age: Global Warming Since 1998


by Bill Chameides | October 28th, 2008
posted by Erica Rowell (Editor)

Permalink | 31 comments

Has the sun set on global warming? Or is it a case of not seeing the forest through the trees?

This is the third post in a 4-part series on the connection between the sun, sunspots, and climate.

You don’t have to search too hard to find a skeptic’s blog proclaiming that global warming “stopped” in 1998. Oh happy day if it were true, but sadly it is not. Why do I say this? I’ve looked at the data.

Take a look at the graphic below, which shows the average global temperatures from 1990 to the present. The green diamonds show the 5-year averages for the periods from 1988–1992, 1993–1997, 1998–2002, and 2003–2007. Each successive diamond appears at a higher temperature than the one before. In other words, global temperatures have been increasing over the past 15+ years — global warming has not stopped.

Global temperature trends since 1990. Solid line with small dots indicate the annual averages. The green diamonds indicate the 5-year averages. Data taken from the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory: http://cdiac.ornl.gov/climate/temp/temp_table.html

If you look at the temperatures in the graphic year by year, it’s easy to see why someone might think that the warming has stopped. After all, there was a huge temperature maximum in 1998. Since then, only 2005 had average temperatures equal to or perhaps slightly greater than those in 1998.

Other Posts in This Series
Part 1: Total Solar Irradiance
Part 2: Sunspots
Part 3: Global Warming Since 1998
Part 4: Predicting Future Climate

Eyeballing temperatures from 1998 onward might lead to the inference that temperatures have not increased at all -– that global warming has stopped. But wait. If you do the same eyeballing exercise starting in 1999 or 1996 you would conclude that there has been a rapid increase in temperatures. Moreover, if you were back in 1992 or 1993 and had done the same eyeballing exercise back to 1990, you would have concluded that global warming had stopped; and you would have been wrong.

So what’s the problem? It comes from a confusion between inter-annual and short-term temperature changes and the longer-term changes in temperatures that are relevant to the issue of climate change on decadal time scales.

There are any number of factors that cause global temperatures to rise and fall. Solar activity is one –- as the sun goes through its 11-year sunspot cycle, solar radiation goes up and down causing global temperatures to fluctuate up and down. El Nino and La Nina oscillations in the South Pacific Ocean also lead to relatively warm years (El Nino) and cool years (La Nina).

The years 1998 and 2005 are interesting to compare. Depending upon the method used to analyze the temperature data, scientists have concluded that either both years tied for the warmest temperatures on record or 2005 was slightly warmer (see here or here).

That 1998 was unusually warm is not surprising. It was a year with an unusually strong El Nino and with the sun close to its 11-year maximum. By comparison, the sun in 2005 was near the minimum in its cycle, and the year began with a weak El Nino that dissipated by late spring. A reasonable explanation for 2005 being as warm or warmer than 1998 without the benefit of a solar maximum or strong El Nino includes warming from greenhouse gases.

Global warming from greenhouse gases does not occur in a vacuum; it occurs simultaneously with other factors that affect global temperatures like solar variations and El Nino/La Nina oscillations. As I discussed in my previous posts in this series, these other factors can cause short-term ups and downs in global temperatures. But the question for global warming is whether they cause a net temperature change. To determine that, we filter out the short-term fluctuations by using longer term averages (such as the 5-year averages shown in the graphic), and when we do, the upward trend in global temperatures comes through loud and clear –- take a look at the green diamonds.

In my next and final post in this series, I’ll take a look into the crystal ball and examine where climate might go in the coming decades.

Other Posts in Global Warming and Predictions of an Impending Ice Age

Part 1: Total Solar Irradiance

Part 2: Sunspots

Part 4: Predicting Future Climate

filed under: climate change, El Nino, faculty, global warming, La Nina, temperatures
and: , , , ,

31 Comments

All comments are moderated and limited to 275 words. Your e-mail address is never displayed. Read our Comment Guidelines for more details.

  1. Mike
    Jun 3, 2009

    Has anyone considered that, because most all plants grow faster and create more sugar with increased CO2, the increased rate of converting sun radiative energy into a chemical potential MUST therefore decrease the amount of reflected IR back into the atmosphere. I kinda doubt the IPCC included anything like that in their models but I think it ought to be measured and then considered if it is a significant factor. ” title=”Radiation to chemical storage rate

    • wendy
      Aug 18, 2009

      Mike, An interesting idea. But: 1. Do you mean reflected sunlight? IR is radiated from the earth’s surface and is not reflected by plants. 2. Only a very small percentage of the sun’s energy incident on a plant goes to photosynthesis, and it is not clear that a change in photosynthetic rates changes the reflectivity of the plant anyway. 3. I suspect the effect if any is quite small. ” title=”Dr. Chameides responds –

      • Mike
        Aug 18, 2009

        Your clause in #3, ‘if any’, can be summarily dismissed by the fact that we are digging up the very solar energy that was so captured – in the form of coal. The energy in coal is energy that came from the sun that was NOT reflected back out to space in any form / wavelength; energy mostly in the form of visible and longer UV that was not transformed into IR to further heat things up on it’s way back out to space but, instead, converted into a chemical potential. So while you are certainly free for now to suspect that the effect might be ‘quite small’, you do not have a leg to stand on implying that the effect might not exist. Exist it most certainly does. Agreed? Therefore, given the fact that every erg of solar energy so converted to chemical potential via photosynthesis is solar energy that is captured and stops right there, is precisely an amount that is not reflected at all and, that an increase in the rate that the solar energy is being captured would necessarily further decrease the amount of solar energy that goes into heating, I contend that what can be stated is limited to a discussion of the magnitude of such a decrease in the overall scope of “global warming”; it cannot be stated that the increase has no impact on the energy balance equation at all. To assert not having ANY impact would violate fundamental physics. Again, while I certainly agree that the magnitude may turn out to be small and insignificant, the notion that it might not exist and/or cannot have any impact is patently untrue. The whole point of my original post was to bring light to just one, perhaps minor, aspect of the complexity of our living earth that was left out of the modeling relied upon by the IPCC. That modeling remains the sole basis for the assertion that ‘human generated CO2 causes global warming’. Even the IPCC itself ADMITS that the entire climate system was NOT fully represented within their models, (such as water vapor cycling), and, of that, they did not further detail the breadth of what else they believe they may have missed. The relationship between plant growth rate and the capture of solar energy may be very small but it is very real and an example of something they did not consider. Many small things not considered can add up to a rather large mistake… What else did they miss? ” title=”Coal

        • wendy
          Aug 18, 2009

          Mike, Not agreed. You say: “…an increase in the rate that the solar energy is being captured (by photosynthesis) would necessarily further decrease the amount of solar energy that goes into heating…” Not really. Eventually the solar energy stored as chemical energy in plants is eaten and burned by some organism and in so doing releases that stored chemical energy as heat – the same heat that would have heated the planet as solar radiation in the first place. Because of conservation of energy it is a zero sum game. Now it is true that a tiny, tiny amount of the plant material ends up getting buried in ocean sediments (and is the stuff that will become fossil fuels in ~ 100 million years or so). But the energy impact of that is minuscule, far smaller than the heat released by burning fossil fuels which itself is insignificant from the point of view of the global heat budget. Now with regard to models: of course climate models do not include every process of the climate system. They focus on the ones of significance for the problem at hand. For example, it would not make sense to require the designer of a bridge to take into account the effect of ant colonies on the structural stability of the bridge. (And note please observe the 275 word limit.)” title=”Dr. Chameides responds –

          • Mike
            Nov 9, 2009

            Re: “… Eventually the solar energy stored as chemical energy in plants is eaten and burned by some organism and in so doing releases that stored chemical energy as heat …” I’m sorry to keep disagreeing with you Dr. Chameides but this is ignoring the issue of TIME. Again coal is my example where “solar energy is stored as chemical energy” but is NOT eaten and therefore sequestered away for who knows how long and not in oceans. Granted that we do not have tropical peat bogs like back in the Carboniferous but we still do have peat bogs sequestering carbon/energy and, the faster they grow, – the faster they sequester. (What if the bridge is made of wood and they are carpenter ants? 🙂 As for models, the IPCC admits that water vapor is the greatest GHG (it’s no ‘ant colony’) but then ignore it’s obvious negative feedback role altogether such as in the form of tropical thunderstorms that carry latent heat of water evaporation high into the stratosphere releasing the heat it collected on the ground well above ~99% of most all GHG’s. Such mechanical transfer of heat energy via convection is not considered in any models referenced by the IPCC to my knowledge, (I believe they said such things were “too complex”). Richard Lindzen and Yong-Sang Choi recently published a paper using ERBE data to show there is a strong negative feedback going on in stark contrast to the positive feedback assumptions made in the IPCC models. I suggest that you take a look: http://www.drroyspencer.com/Lindzen-and-Choi-GRL-2009.pdf ” title=”Coal again…

  2. alan falk
    Nov 15, 2008

    i feel so meek… no phD, no history of climatology in my resume… just some EE education at RPI a few or more decades ago.. but the graph you led this part of the series with struck me immediately as a nice approximation to a step function with most of the higher-level harmonics removed. therefore, your look at five-year average temperature points wouldn’t have any more validity in supporting your conclusion than to look at the five-year average of a step-funtion temperature increase and then concluding that the “long-term trend is constantly upward.”. …….. and the data would back it up! the data you show include non-increasing maxima with increasing minima. extrapolating the 5-year points is graphically misleading and “bad math” in my not-so-humble-opinion. no, still no phD, but i’ve been looking at graphs since the mid-60s or so [1960s, that is!] and my mind is nicely wired for seeing and extracting trends from graphs. the BSEE and PRI training didn’t hurt, either. cheers, and thanks for the posts! i like thinking… http://www.plusaf.com ….” title=”nice fourier graph…

    • erica
      Nov 17, 2008

      Dr. Bill Chameides replies – Alan, yes, analysis of higher level harmonics is a powerful way to deconvolute a trend and tease out the various modes of variability, and looking at a single five-year average cannot be used to infer a long-term trend — neither of which was the purpose of the post. It has been argued by some that there has been no global warming since 1998 — it is these folks (and not me) who are claiming to see a “long-term” from a short record. The fact is that the data do not support their conclusion. This was shown in my post that five-year averages in temperature have increased over the past 15 years. The last 5-year average was warmer than the previous which was in turn warmer than the previous. You can track that trend back over the decades if you want – the conclusion holds. Global warming has not stopped.” title=”Global warming has not stopped

      • alan falk
        Nov 17, 2008

        thank you Dr. Chameides… and that’s why i keep putting graphs on my global warming page… eg, http://www.plusaf.com/lessons/globalwarming.htm#tempgraphs how far back is “far back enough” to make a point? ymmv… your mileage may vary… :)” title=”always a “yes, but”, eh?

  3. Alfredo
    Nov 6, 2008

    The reason why I’m still a skeptic about the role of CO2 in global warming is that correlation is not causation. Many things correlate with temperature increase. Without a clear understanding of climate we can’t be certain it’s all due to CO2. The increase in CO2 doesn’t explain why there’s such a huge dip in 1999 and 2000. It doesn’t explain why we had a small ice age that lasted between 1650 and 1700. If we were living during the Little Ice Age in 1650 we would be looking for reasons why we created that ice age and we would be looking for ways to reverse it. Do scientists have irrefutable proof that global warming is not a natural phenomena? We only have about 60 years of data for CO2 because supposedly we didn’t produce as much CO2 before. Is that enough data to support the global warming hypothesis when the earth goes through so many cycles of cooling and warming? I appreciate your trying to warn us about global warming, but I don’t see any real science here.” title=”Where’s the proof that it’s all due to CO2?

    • erica
      Nov 10, 2008

      Dr. Chameides replies: Alfredo – I agree 100 percent. A correlation does not mean causation. The conclusion that CO2 is a cause of global warming is not based on correlation; it is based on physics. I’ve already explained why we do not expect all the dips and peaks in temperature to correlate with CO2. It’s fun to think about what the folks back in the seventeenth century might have thought about the Little Ice Age, but is it relevant? We’ve come a long way scientifically since then, don’t you think? If they saw a jet aircraft flying overhead, they would have probably concluded it was a huge bird. They would have been wrong. But that would not mean that we would be wrong concluding it was a jet.” title=”It’s All in the Physics

      • mark connolly
        Nov 11, 2008

        It’s clear from the posts in this series that everyone here knows a lot about climate science; at least as much as we can know with our imperfect knowledge. While it is crucial for scientists and everyone else to be aware that there is no such thing as an exact science, surely given the potential risks we may face from our own actions it is beside the point. The fact is the climate IS changing and no-one knows 100% why. It is better to make precautionary changes to ensure our role is discounted. Even if climate change is not caused overwhelmingly by humans, resource and environmental collapses have happened consistantly as a result of human actions. The world will survive (as it always has) whatever nature, the universe or humans throws at it. The question is whether we are destroying the planet’s carrying capacity for a species such as our own. Clearly we are- any acts to minimise our impact will mean future generations will have the best possible chance to survive changes that are beyond our control. The precautionary principle is a wise one, especially given the overwhelming consensus that our pollution is taking us on a runaway train. Hopefully in 50 years there will be a world fit enough for you lot to score academic points. http://www.facebook.com/pages/Sustainable-Earth/14936967018 ” title=”All very interesting but…

        • Tilo Reber
          Nov 18, 2008

          “The fact is the climate IS changing and no-one knows 100% why.” Yes, this has been the case for about 4 billion years. “It is better to make precautionary changes to ensure our role is discounted.” There is no reason to discount our role. There is absolutely no evidence that we have a role that has serious concequences for the planet. However, spending trillions fighting a non problem can seriously undermine our quality of life, and it can actually be life threatening to third world countries that cannot afford technologies more expensive than fossil fuels. “resource and environmental collapses have happened consistantly as a result of human actions. ” Sorry, I’m not buying any guilt trips. If all of this collapse has happened, then why do we have more human beings living better on the planet than ever in its history. Why is the biomass of the earth increasing? “Clearly we are- any acts to minimise our impact will mean future generations will have the best possible chance to survive changes that are beyond our control.” Future generations will have the best chance of surviving if they have lots of highly sophisticated technology to help them survive. A romanticised notion of some kind of benign, pastoral planet that never changes is absurd. And how is our famous canary in a coal mine doing? http://tomnelson.blogspot.com/2008/10/churchill-area-fall-aerial-survey-found.html” title=”Doom and Guilt

          • erica
            Nov 19, 2008

            Dr. Chameides responds – Tilo, Thank you for your comments, but: (i) the technical aspects of your comments are largely incorrect; (ii) you attribute statements and opinions to me that do not apply. For example, where in my post have I suggested that I am against technology or that I subscribe to a benign pastoral planet that never changes? Do try to keep your comments on topic.” title=”Try to keep comments on topic

          • mark connolly
            Nov 19, 2008

            Dr. Chameides Tilo’s comments were in response to my posting, so in reply… I’m not denying that climate change can happen as part of natural cycles, the evidence proves it so we are in agreement there. The question here is whether it is worth spending trillions to mitigate the human element in current climate change- something the majority of scientists and an increasing number of CEO’s and politicians say is the primary cause of current change. It’s not a question of money, clearly if we can bail out irresponsible business and inject trillions within months into the stock market, there’s more than enough money to pay for the programmes of Nicholas Stern or anyone else. You say there is absolutely no evidence that we have a role that has serious consequences for the planet- numerous reports by governments, intelligence agencies, the military, corporations and NGO’s say differently. All these reports be thousands of people may be wrong- the models are only as good as their programmers after all. If that is true then it will be a humbling experience where our best scientists can go back to the drawing board and come up with some new theories on how things work.I’d rather laugh and be wrong in fifty years than see my children cry because a myopic boomer generation refused to go on a guilt trip. I know that’s such a downer man but frankly I and a growing number of folks who will be around in 2050 are fed up with denial junkies who only see a problem if it is in their face. I agree that a romanticised notion of some kind of benign, pastoral planet is absurd. I didn’t suggest it, nor do I want it. Technology is the key, but it has to be technology which works with nature and people, not against. You ask why biomass is increasing…well as I’m sure you know a temporary increase due to changin climate patterns has been predicted, but in the decades ahead much of the gain is expected to disappear. As for canaries, take a look up…you will see the mine shaft is filling up. ” title=”Insanity: doing the same thing over and over again and expecting different results.

            • erica
              Nov 20, 2008

              Dr. Bill Chameides replies – Thank you, Mark. Let me add one thing. Not everyone agrees that going to a low-carbon economy with little greenhouse gas emissions is going to be bad for the economy. You might read Thomas Friedman’s new book – for more info check out my post on his visit to Duke: http://www.nicholas.duke.edu/nicholas/insider/thegreengrok/friedman” title=”Low-carbon economy could be good for the economy

  4. Tilo Reber
    Nov 3, 2008

    Bill: “Why do I say this? I’ve looked at the data.” No, there actually hasn’t been any warming for the last 11 years. Why do I say this? I have looked at the data. In fact, I downloaded all of the raw data from HadCrut3, RSS, GISS, and UAH. I used the monthly data, and this allowed me to get a picture of what was happening clear up to Sept. of 2008. Then I simply put that data into an Excel spreadsheet and told Excel to plot it for me. After that I told Excel to add a linear regression trend line to each of the data sets. Very simple, no tricks. Anyone and everyone can reproduce what I did and see for themselves. Here are the results. http://reallyrealclimate.blogspot.com/2008/10/updated-11-year-global-temp-anomoly.html Double click the chart to get a larger image. ” title=”The problem with outdated data

    • S2
      Nov 25, 2008

      Tilo, I can’t understand how you get your graph. You have 1997, 2001 and 2006 as being nice and warm – while 1998, 2005 and 2007 look distinctly chilly. This doesn’t agree with any of the datasets you claim to have used. ” title=”Tilo’s graph makes no sense

  5. Joe D'Aleo
    Oct 30, 2008

    Bill I was your student at NYU in the 1970s. See the real temperatures from Hadley and UAH MSU since 2002 here. http://icecap.us/images/uploads/MSUCRUCO2.jpg And for the USHCN version 2 (with urban adjustment removed, 5 of the last 7 decades have shown cooling. See http://icecap.us/images/uploads/CO2HCNlongterm.jpg. I prefer not to use the global data bases with suffer from dropout, missing data, poor siting and little or not urban adjustment. CO2 has precious little to do with climate change. I find much stroinger correlations between ocean multidecadal cycles and TSI and temps than CO2. See my website htpp://icecap.us All the best Joe D’Aleo” title=”Cooling since 2003

    • erica
      Oct 30, 2008

      Dr. Chameides responds – Joe, It’s great to hear from you, but there is a problem — I never was at NYU during the ’70s or otherwise, so I don’t think I can take credit for any of your education. As for the temperature trends: 1. The UAH MSU data: As I am sure you know, there have been major questions about and revisions needed for the temperatures inferred from the MSU satellite measurements. With recent corrections, those data are consistent with global warming from greenhouse gases. For example see: https://publicaffairs.llnl.gov/%5B…%5D/NR-08-10-05p.html 2. The Hadley CRU data: The trend lines you show in your links give a misleading impression. It is easy to get a negative trend using data covering a short period of time, especially when the data begin with a relatively warm period (2002) and end with a relatively cool period (the end of 2007). As I explained in my post, it is far more instructive and relevant to look at a longer-term trend. And if you do this, both the Hadley data, which you apparently prefer, and the GISS data, which I used in my post, give essentially the same result: 5-Year Average Global Temperature Anomalies (C) 1988-1992: 0.27 (GISS) | 0.16 (Hadley) 1993-1997: 0.29 (GISS) | 0.20 (Hadley) 1998-2002: 0.45 (GISS) | 0.39 (Hadley) 2002-2007: 0.55 (GISS) | 0.44 (Hadley) Both data sets show a continuing warming trend. For both data sets, temperatures over the past 5 years were warmer than the previous 5 years, which were warmer than the previous 5 years and so on. There is no global cooling, there is warming. Sources for the data: http://cdiac.ornl.gov/trends/temp/hansen/hansen.html and http://www.cru.uea.ac.uk/%5B…%5D/hadcrut3vgl.txt And finally, the fact that you see correlations on one time scale does not mean that there aren’t drivers of climate working on longer time scales. Moreover, since there are multiple drivers of climate operating on multiple time scales, there is no reason to expect a simple correlation with any one single parameter. Anyway, thanks for your comment, and I hope whoever taught you at NYU did a good job.” title=”Warming Trend

      • Steve
        Nov 1, 2008

        I went to the CRU link you provide at the bottom of your answer to Joe. Looking at the thick black line, I cannot see where you are getting continuing warming from. It’s just not there. Yes, I know that if you take this average, that time scale etc. But this is all smoke and mirrors stuff. Us laypeople have to look at simple graphs, and the very graph you link to (CRU) doesn’t show your warming, it shows a clear dip in temp for the past few years. [Note, it looks like it’s level, but a small dip is visible]. But I gave up on surface temps some time back, as they quite clearly are corrupted by their surroundings or worse “adjustment” or extrapolation (GISS – and that’s why you shouldn’t use it Bill!). I’ve been following the UAH and RSS data instead. When you look at that and see no net temp increase in decades of supposed CO2 forcing, then you can come to no other conclusion other than that global warming simply does not exist. Your ‘temp change’ graph doesn’t include the drop in temps at the end of 2007. Why not? To exclude it leads me to think you are not being honest with yourself, let alone your readers. This year’s CRU global anomaly will be 0.3 or even 0.2 – when for the past seven years it’s been 0.4. http://www.cru.uea.ac.uk/cru/data/temperature/hadcrut3gl.txt This at the very least shows flattening, if not falling. Quite simply Bill, you’re wrong.” title=”CRU

        • erica
          Nov 2, 2008

          Dr. Chameides responds – Steve, my friend, we can focus on all the little dips and blips in the data and argue whether there is an upward trend or a downward. In the end it’s an eyeballing exercise — a judgment call. Reasonable people may see different things. That’s why they invented statistics — they provide an objective analysis. If the averages are increasing, they are increasing. It’s as simple as that. In this case: The average temperature over the last 5 years was warmer than the average temperature over the previous 5 years, which was warmer than the previous 5, and so on. Don’t take my word for it — you can calculate it yourself. Clearly there has been a continuous warming. Does that mean that every month was warmer than the previous month or even that every year was warmer than the previous year? Of course not, for the reasons I explained in my 4 posts in this series. Some other points: I gather that you “gave up on surface temps” because you believe they are corrupted by local effects, etc. What about the warming of sea surface temperatures – no local effects, no adjustments. The temperature change graph I showed does not include the “drop in temperatures at the end of 2007″ because it was a plot of ANNUALLY AVERAGED TEMPERATURES. And by the way even with that drop in temperatures at the end of 2007, 2007 was the third warmest year on record. And the 5-year average that I calculated for the past 5 years included that drop in temperatures, and even so the average temperature for the period from 2203-2007 was warmer that that of 1998-2002. So no smoke and mirrors, just the data.” title=”The Data

          • Steve
            Nov 2, 2008

            Bill, thanks for relpying. Yes, I take your point about 5-year averages according to GISS and CRU, can’t deny it. But that’s not the only game in town, and you know it. The reason I wanted you to take another look at the CRU site is because of that thick black line. What’s that curl at the top tell you Bill? But more than that, what of UAH & RSS? I didn’t mention sea temps. Have you seen how they were taken in the past? Do you think that was ‘scientific’? What do we have with the ARGO bouys? What I actually said was that I only bother to see what the UAH & RSS are saying – as that’s where the weather is, and that’s where temps get nicely mixed. CO2 has never caused climate change and never will. The tiny forcing it provides is countered by nature’s checks and balances. Surely the last few years teaches us that? CO2 emissions have risen dramatically, whereas the temperature (according to UAH & RSS) has not. Why do these graphs show no net warming since 1980? The smoke and mirrors is that you prefer to use GISS rather than UAH & RSS. I know why, and so do you.” title=”UAH & RSS

          • Alex Kartashov
            Nov 11, 2008

            “In this case: The average temperature over the last 5 years was warmer than the average temperature over the previous 5 years, which was warmer than the previous 5, and so on. Don’t take my word for it — you can calculate it yourself” As you are undoubtedly aware, you can calculate different types of statistics on the same data. In this case, 5 years is a voluntarily chosen interval. Sure, it’s a less volatile measure than 1-year statistics. But what happens if you shift a scale 1 year to the right, to include year 2008? The result will be different. That simple exercise just shows that the estimate based on your method is not robust. Another objection is the post hoc character of your choice. Why 5 years, not 10, 20 or 3? Methodologically, you can not base your conclusion on 20 years of observation (showing positive trend) and ignore the last 7 years showing the negative trend. These are intervals well within the same order of magnitude. (Sorry: just to introduce myself, I have a PhD degree in marine ecology and currently am working on my degree in biostatistics, so the matter is more or less familiar to me)” title=”That’s why they invented statistics

            • erica
              Nov 11, 2008

              Dr. Chameides responds – Alex, I would be happy to include 2008. There’s only one problem – 2008 hasn’t ended yet… With regard to the interval, choose 10 or 20 instead of 5, and you get the same result: the most recent interval is warmer than the previous. Shorter than 5 is not very useful because it is so short. Again, look at the temperature record over the past 100 years. Lots of short-term swings over a few years but a long-term upward trend. And I have NOT ignored the last 7. Clearly they were included in the averaging.” title=”Same Results With Other Intervals

              • Alex Kartashov
                Nov 11, 2008

                I did not mean that you do not include it on purpose. My point was that when analyzing such a random process, the estimations of trends are only as good as they are. And the example of year 2008 noticeably changing the results is a good one. I do not argue that 20 years show the positive trend (whatever is the averaging interval). My other point, again, was that if we are making conclusions based on 20 year interval, we should pay some attention to the fact that the last 1/3 of this interval show the reverse trend. Would you agree with it?” title=”no offence meant

                • erica
                  Nov 19, 2008

                  Dr. Chameides responds – Alex, It does not show a reverse trend. The last 5 years were warmer than the previous, etc.” title=”No reverse trend

                  • Alex Kartashov
                    Nov 19, 2008

                    Excuse me, but I said: ” the last 1/3 of this interval” I am talking not about the 5 years compared to the previous 5, which makes a half of the interval, but about the trend within the last 7 years: http://icecap.us/images/uploads/MSUCRUCO2.jpg, and you have seen this plot before. Let’s wait till we have full data on 2008, and then we’ll compare two 5-years intervals, if you insist on this measure. If it does not show increase, would you be as ready to claim that there is no warming as you are now to claim there is? ” title=”trend in the last 1/3 of the 20 years period

                    • erica
                      Nov 20, 2008

                      Dr. Bill Chameides responds – OK, so you want to focus on the temperature “trend” over the last 5 years. It is interesting to speculate on the reasons for the year-to-year variability in temperatures over the past few years. And I have done that very thing in this blog, but it is not relevant to this discussion. Look at the temperature record over the past 100 years. There are numerous dips in temperature that last a few years or even more. But the long-term trend is upward. Why are you so convinced that this is not one of those dips? Do you have any special insight?” title=”Long-term trend is upward

                    • Alex Kartashov
                      Nov 20, 2008

                      No special insight into this last period. Picking the last 7 years (not 5, BTW, I said 7) does not say much; why are you so convinced that 20 years you picked provide such a great quantum leap? You are aware, of course, of the downward trend for along period, from the 40s to the 80s – why don’t you pick this period? Now, you talk about the las 100 years – why not compare it with the previous centuries? You know abouth the much warmer period around 1000 AD and of a colder period afterwards. So, again, if it’s a serious discussion, than you should not cherry-pick the periods that fit your theory. If we agree that 7 years mean nothing, and decline for a few decades in the middle of the XX century does not mean anything either, than why would you produce and discuss your plots at all? Second point is the following. You ask me: “Why are you so convinced that this is not one of those dips?” Well, the same question may be addressed to you: what does the evidence say about the natural fluctuations of the temperature? How can we be convinced that this particular trend, observed for the voluntarily choosen time interval, is not a random effect, or a part of a cyclical change? The difference is that I don’t ask the world to spend trillions on urgent measures to warm the planet. ” title=”long-term trends

                    • erica
                      Nov 24, 2008

                      DR. CHAMEIDES replies – Alex, Alex, Alex – Is it really necessary to go over the same points over and over again? We have clearly gotten to the point of diminishing returns on this thread. So let’s just leave it there.” title=”Point of diminishing returns

©2015 Nicholas School of the Environment at Duke University | Box 90328 | Durham, NC 27708
how to contact us > | login to the site > | site disclaimers >

footer nav stuff