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:
Temperatures plummeted over the last year (2007-2008). If you look at this data from the Met Office Hadley Centre you can clearly see that in one year alone global temperatures dropped .6oC, an amount equal to the entire warming over the 20th century claimed by the IPCC.
(click graph for a larger image in a new window)
Answer:
This argument represents a fundamental misunderstanding of the difference between weather and climate. Climate is generally defined as the weather conditions averaged over a long period, usually around 30 years. One can not discern a trend in climate change by looking at small numbers of years, much less a single one. On top of that, this fallacious objection is using global temperatures in a single month, not even an entire year! An even cursory look at the graph above reveals the very noisy nature of monthly temperatures, even when averaged over the entire globe. The particular Jan07 to Jan08 drop used for this argument is indeed large, but it is by no means the only place you could pick to draw a steep line, either up or down. Look at the huge leap up from month 219 to month 231 or the sudden drop from month 152 to month 164 (I am only using intervals of 12 months to avoid seasonal bias). This is very noisy data and those dramatic flucuations turned out to be just that: noise.
Discerning a trend from noisy data is one of the most basic processes in scientifc research, so even though this argument has a naive appeal to the majority of us with no statistical training, you can be sure that any scientifically trained individual trying to make a case for cooling out of this graph is not being intellectually honest. Please consider any source of this argument as very unreliable, either by being very uninformed about basic scientific processes, or very dishonest, hoping to tke advantage of less informed people.
So what do we see when we step back and look at the whole picture?
(image taken from this page)
Clearly the last few years, far from erasing the entire warming of the 20th century, have remained far above the global baseline (1951-1990 average). We can also see that even in globally and seasonally averaged and smoothed data, there are still numerous peaks and troughs that are irrelevant to the long term trends. On this graph, the last 4 or 5 years do look as though the trend has paused and even reversed but this is actually a misleading artifact of how the graph was produced. If you look at the page on the Hadley site that describes the smoothing method used, you will see that it is actually too soon to know what the real 2007 trend direction is. The smoothing they use requires 10 years of data on either side of the year in question. So though the trend today may in fact be down, we will not know this for sure until ten years from now. Hadley centre made the decision to continue the line until 2007 to avoid the appearance of incomplete data despite the fact that the last 10 years are less and less meaningful.
There is no convincing reason to think that the well established and attributed long term trend has reversed nor that it is likely to for many years to come, even if effective global actions were taken today to stop emissions of greenhouse enhancing gases like CO2 and CH4 (methane). Short term influences like La Nina and volcanic interruptions may cause dips and slow downs but the elevated levels of greenhouse gases already in the air will eventually overwelm the long term.
And before you let anyone argue that the uncertainty about today I just described just means we need to wait ten more years, please recall that we have done that and more already. 20 years ago James Hansen was telling the US senate that warming was real, significant and anthropogenic (human caused) and the projections he provided have been largely borne out by what has been observed. The skeptics have already made us wait, and the three IPCC assessments that came out in the meantime have been more and more emphatic in their conclusions. The wait is over, the trend is clear and the casue is well understood.
It is a telling and egregious double standard for those voices that for the past twenty years have told us to wait and see are now claiming the trend is over based on such a small blip in the mountain of data.
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.
"Temperatures in 2008 have plummeted" is also posted on the Grist website, where additional comments can be found, though the author, Coby Beck, does not monitor or respond there.
Environment
Physical Science
Comments
I am not a skeptic that there is global warming, nor am I skeptical that the CO2 we're producing is having some effect. I am skeptical about the severity of the effect, and I am deeply, deeply skeptical about the efficacy and cost-benefit of the various policies and protocols that are recommended to combat it, but I doubt there's anything productive we can talk about on that subject.
Next, let me say that I agree with you 100% - you cannot judge a trend based on a single year's datapoints. The people who claim that Global Warming is over because of a one-year drop are foolish.
But, there is another side to this.
Everytime there is a flood, people in the media, politicians and science pundits, etc, all claim that it is due to global warming. If a month is warmer than usual, they blame global warming. If a month is colder than usual, they blame global warming. If a month is wetter than usual, or dryer than usual. IF there are more storms, or there is a drought. More hurricanes this year - AGW. Fewer hurricanes? AGW. Literally, almost every anomalous weather event is attributed to Anthropogenic Global Warming.
And no one from the 'IPCC' crowd corrects them, at least not in any structured and consistent way. And why should you? These people are useful idiots whose distortions and mischaracterizations of 'weather as climate' are helping keep AGW front-and-center in the news.
I am not going to claim that 'you started it'. I don't know how we got to the point that every adverse weather event is blamed on AGW, and every drop in the temperature is 'proof it didn't happen'. But your "side" is, as far as I can tell, just as guilty of obfuscation and talking points as the other.
This is not to say that they are right, and you are wrong. But your lecture would hold far more moral weight if you also made a point of blogging on errors from those who support your cause as well.
Posted by: jb | September 8, 2008 2:44 PM
Plotting the first graph with the feb->july data might also be a good response. It would show that the "analysis" is old, incomplete, and pure cherry-picking. The last graph on http://hadobs.metoffice.com/hadcrut3/diagnostics/global/nh+sh/ has the longer record, and the data to make the extend to now.
Your second graph does answer the real question, but doesn't use the analyser's own analysis against him.
And good point on the double standard.
Posted by: Dave X | September 8, 2008 3:00 PM
Note that the effect of global warming on hurricanes in particular remain an unresolved issue - see Chris Mooney's excellent book Storm World on this topic, or any of several articles on realclimate.org (just search their site for 'hurricanes'). There is evidence that AGW is making hurricanes more intense globally, and more common in the Atlantic. But there's conflicting evidence that warmer temperatures make hurricanes more vulnerable to shear, and that AGW contributes to stronger and more frequent El Ninos, which result in fewer and weaker hurricanes in the Atlantic (but more and stronger hurricanes in the East Pacific.) These conflicts are not yet resolved. There are three things you can do about this: (a) be patient, (b) donate $20 a paycheck to some promising hurricane research, or (c) become a hurricane scientist yourself.
Interestingly - making the case for slowing global warming, can, in my opinion, be solidly made entirely without mention of hurricanes. First - the evidence that oceans are rising is very strong, and the evidence that sea level rise at least 30 cm by 2100 is also very strong. It's also possible sea level could rise much further - credible estimates range up to 1m by 2100. 100 million people live on land that would be underwater with 1m sea live rise. Not to mention thousands of miles of important roads, hundreds of power plants, untold numbers of important petro-chemical plants, and many other industrial structures. Next, consider farming. The NH jetstream is already moving north, and areas south of the jetstream are already getting dryer, forcing farmers to shift crop varietals, and change farming methods. Global warming will make it harder to feed the world. In particular - note Pakistan, India, Iran, and China are all highly vulnerable to this risk. All have a history of political volatility, three have a history of religious volatility, three have nuclear weapons. America - itself no stranger to war - is also at risk, though here we have the knowledge and the technology to cope, although the political and business will seems determined to push in the wrong direction. I could go on - global warming has effects on insect pests, plant pests, infectious disease, all of which present some risk. But none of these things are as photogenic as hurricanes. :-( .
Posted by: llewelly | September 8, 2008 5:09 PM
I agree 100% with jb, and I would add this:
If temperatures had increased steadily from 2000 to the present, the alarmists would be jumping up and down screaming about it from the rooftops. They wouldn't be saying "this is weather not climate"
Alarmists (generally speaking) have a double standard, and it's more than just a sign of intellectual dishonesty. It shows a fundamental and wilful ignorance of the core principles of science. Evidence should be seen as confirming only if the hypothesis was actually at risk.
Let me put the issue another way: If the AGW hypothesis is correct, can we basically exclude any weather or climatic trend? If not, then the hypthesis is non-scientific and meaningless.
Posted by: smile4me2222 | September 8, 2008 5:40 PM
smile4me2222,
If the global temperature trend were to diverge to a statistically significant degree from the trend predicted by the models (which incorporate what is currently understood by scientists about the climate system) then yes of course our understanding of the climate system would have to be questioned.
To get a feeling for how you go about doing this, have a look at Tamino's 'You bet' blog post where he explains how you might go about it in the context of a bet.
By contrast, currently the skeptics don't even have an understanding of the climate system that is coherent enough to model.
Posted by: Craig Allen | September 9, 2008 3:05 AM
"Discerning a trend from noisy data is one of the most basic processes in scientifc research, so even though this argument has a naive appeal to the majority of us with no statistical training, you can be sure that any scientifically trained individual trying to make a case for cooling out of this graph is not being intellectually honest. Please consider any source of this argument as very unreliable, either by being very uninformed about basic scientific processes, or very dishonest, hoping to tke advantage of less informed people."
Hmmm, who's being disingenuous here? I could apply the IDENTICAL argument you've made (covering the period 1850 to now) to the temperature graph of the last 1000 years (the one from the IPCC report). In this, the rise of 0.6 would simply be noise, in the same way the drop you point out can also be considered noise. You can't bang on about how important stats and science are but then make statements like "Climate is generally defined as the weather conditions averaged over a long period, usually around 30 years." These are not made by people with "statistical training" or "scientifically trained" individuals - where on god's warming earth does 30 come from, except as a number which aids your argument?
[Hi John,
Please see this post for an answer to the above]
Let's talk stats. There is no warming problem at present - carbon has gone up by 30% in the period of your graph, and the temperature remaining as it is now would be fine.
This is the null hypothesis.
[Have a look at this article wrt the Null Hypothesis.]
The alternative hypothesis is that carbon emissions will make things bad. Show me the data which allows you to reject the null hypothesis and state your confidence limits?
[Please refer to the IPCC reports]
Posted by: John | September 9, 2008 3:40 AM
Please use the more accurate plural with "data"; data show, data do not "shows." A data point, or datum, is the singular. (Science talk to be gooder must needs be preciser!)
Posted by: detailmaven | September 9, 2008 6:58 AM
Maybe. Also, maybe the point of communication is to convey your intentions, and as regardless of this "error" you know what I mean, maybe you shouldn't be wasting time and, I don't know, point out where I'm wrong.
Posted by: John | September 9, 2008 7:26 AM
Ha - and I actually just read what you said again, and it makes no grammatical sense anyway - it was "allows" which ought to be adjusted, not "shows".
Posted by: john | September 9, 2008 7:29 AM
And while I'm here.
http://www.askoxford.com/asktheexperts/faq/aboutgrammar/data
Posted by: john | September 9, 2008 7:32 AM
Coby, thank you for this. This is a point that I've been trying to get across to others for quite a while.
John, you appear to be confused as to what 'noise' means -- or perhaps assuming that any anthropogenic climate signal needs to predate human activity. I'd like to think you're smarter than this, so I'll assume it's just a misapplication of 'noise'.
I second looking at Tamino's "You Bet!" post, but more pertinent to this discussion is his "Wiggles" post, which elaborates more on the concept of noise.
Oh, and as for the 30-year point, as I understand it, this comes from a combination of physical principles (i.e. longer than 7 or 11 years, which prevents ENSO or the sunspot cycle from impacting the results significantly) and statistical rigor (i.e. minimum number of years for statistical significance in determining trends; I don't know precisely what this is offhand but I'd be surprised if it was less than 15). I do know for a fact that if it were too narrow, short-term weather noise would dominate the long-term climate signal, and if it were too broad too much of the signal would be lost. Although I suspect the exact number (30) is more of a convention than a rule (as the statements I've read are usually phrased like Coby's above), I would be surprised if significantly shorter timescales were considered legitimate by anyone involved in research. I welcome input by someone more qualified than I am here.
For the record, the IPCC's definition of climate is:
Climate in a narrow sense is usually defined as the “average weather”, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.
As near as I can tell, the WMO has used that definition since its inception in 1950. On the flipside, can you give any compelling reason (physical or statistical) why 30 years will not serve as the baseline, and if so, what would you suggest instead?
Oh, and as for the null hypothesis, Coby beat you to it.
Posted by: Brian D | September 9, 2008 3:12 PM
HI John,
I inlined some responses to your first long comment, and you also insprired a new post!
http://scienceblogs.com/illconsidered/2008/09/signal_vs_noise.php
Thanks for commenting.
Posted by: coby | September 9, 2008 3:16 PM
The point is not whether it is noise or not.The point is that CO2 has increased 5% from 2001 and meanwhile temperatures have gone DOWN.The exact opposite of the AGW theory!The WMO may have said that 30 years is optimum for a trend in climate,but that has nothing to do with how much time you need to test an hypothesis.7 years is enough time to show that temperature has de-coupled from CO2 levels.
Posted by: timwells | October 9, 2008 3:23 AM
The point is not whether it is noise or not.The point is that CO2 has increased 5% from 2001 and meanwhile temperatures have gone DOWN.The exact opposite of the AGW theory!The WMO may have said that 30 years is optimum for a trend in climate,but that has nothing to do with how much time you need to test an hypothesis.7 years is enough time to show that temperature has de-coupled from CO2 levels.
Posted by: timwells | October 9, 2008 3:25 AM
If make a trend for this graph, you will find that the trend has been going downwards since 2004.
Posted by: Nathan | November 3, 2008 3:31 PM
Nathan: a 3 year trend has nothing to do with climate. Even the five year smoothing NASA GISS uses shows a lot of irregularity from natural variation (aka weather)
Posted by: coby | November 3, 2008 5:36 PM