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Debunking various denialist myths. Updated July 2010 |
On this page, responses to popular denialist arguments:
Many sceptics point to the last 10 years of temperature records and claim they show global warming has ceased.
This is like watching waves on a beach for two minutes and claiming the tide has stopped rising. It's not long enough. The graph for the last 100 years shows several such pauses, but the long term trend is clear. A 'blind' analysis by independent statisticians repudiated the claim of a cooling trend. Has it really slowed? It is impossible to get a perfect snapshot of the Earth's average temperature at one instant. Satellites don't show everything. Some of the heat may have gone where we have few sensors, such as the deep ocean or under icecaps. Neither can they distinguish ice at 0C from water at 0C, but the latter represents a lot more heat: just as melting ice in the esky keeps the drinks cold for a while, melting ice at the poles temporarily cools the oceans. Recently it was discovered that a lot more ice has melted under Antarctica than had been realised. See http://climateprogress.org/2009/10/10/skeptical-science-global-warming-not-cooling-is-still-happening-ocean-heat-content/. Satellite data do show how much heat is coming in from the sun and that less is radiating back out. The difference is being stored somewhere, but current measurements only find about half.
For such reasons, the graphs are pretty erratic over periods of ten or 15 years. You have to look at periods of 25 or 30 years before a consistent picture emerges. See also http://climateprogress.org/2009/11/30/climategate-hadley-cru-climate-data/
April 2010: March 2010 was world's hottest March on record May 2010: Hottest Jan-April on record If it really has slowed, why?
In January 2010, NOAA reported that relative humidity in a critical part of the atmosphere had suddenly and unaccountably dropped. This could well explain a pause in the rise of temperatures. The bad news is that would mean the pause is only temporary, and, worse, could bounce back to make up for the pause. Another possibility is sulphate particles. It has been discovered (Science, DOI:10.1126/science.1182274) that the monsoon can thrust such pollution in the stratosphere, where it can last much longer as a sunshade.
Sea level as an indicator
A more reliable test of the short-term trend, Prof Barry Brook points out, is to look at global sea level. The rise comes from expansion of the water as it warms, at any depth, plus any extra water from melted ice. Either way, it indicates warming. Although it only has such data for the last 17 years, this graph shows a very clear picture:
http://www.cmar.csiro.au/ On the other hand, there is a lag in sea level changes, so it does not give quite the latest picture.
Extracts from hacked emails from the University of East Anglia's Climate Research Unit (CRU), popularly known as "Climategate", have provided ammunition for the sceptics. On closer inspection, however, it may be their only fault was to be less open than they might have been.
Some aspects of the furore are certainly a beat-up. The reference to using a certain "trick" with the data is normal techie-speak for a neat method of extracting answers from raw data. There's no implication in this instance that the method is not correct. The purported suppression of converse findings consisted of avoiding lending unwarranted credibility to non-peer-reviewed papers by their juxtaposition with peer-reviewed papers in the same journal.
For a good analysis see http://en.wikipedia.org/wiki/Climatic_Research_Unit_e-mail_hacking_incident. April 2010 update: a second inquiry has cleared the researchers of any wrongdoing, falsification, or bias. It has, however, found fault with their statistical methods and recommends working more closely with professional statisticians.
July 2010 update: a third inquiry, by Penn State University, has cleared Michael Mann of manipulating or falsifying data. "CO2 increase follows temperature increase" In the geological record that is true, and well understood. The change in CO2 was not the trigger in those cases. Rather, some other known event triggered the initial increase, such as large-scale volcanism or increased sun activity. When those other causes declined, the oceans cooled a little and reabsorbed some CO2, leading to further cooling, etc. But those triggers alone do not explain the eventual temperature rise that occurred. The initial rise caused an increase in CO2 (for well understood reasons, such as CO2 release from soils and seas) which then magnified it. This feedback resulted in the eventual rise being far more than it would otherwise have been, and is one of the reasons what we are doing now is so scary. Worse, we are adding CO2 into this system which was not then available for release. (You might wonder why this does not go on forever, leading to more and more GHGs and higher and higher temperatures. The feedback is not a simple straight-line relationship. Eventually, extra GHG has less effect. At the same time, the hotter Earth radiates more heat into space, leading to a new equilibrium.)
However, the fact that the initial trigger was a temperature change on those occasions does not explain the extent of the lag.
The recorded temperatures and CO2 are both at the Antarctic. While the CO2 can be expected to represent the global state, the temperatures may be more local. Andrey Ganopolski and D.M. Roche show that temperature changes tend to be greatest in the Antarctic first, whereas CO2 levels are driven more by temperatures elsewhere. Hence the data show temperature changes preceding CO2 changes.
"The expected 'hotspot' in the troposphere is missing" This is a very technical argument, but it has been adequately debunked. See http://scienceblogs.com/In short, the "hotspot" is not a predicted fingerprint of warming due to increased GHGs. It is predicted to exist regardless of any warming or any cause of such warming. So its absence did suggest the models are not perfect, but it did not point suspicion away from GHGs. Recently it has been shown that the measurements were unreliable, and the hotspot has now been found. See also http://www.csiro.au/news/Are-Climate-Models-Inconsistent--ci_pageNo-2.html. Meanwhile, there is a fingerprint predicted for GHG-induced warming: as the blanket of GHGs holds in more heat in the lower levels of the atmosphere, the stratosphere above cools and shrinks (leading to the darkly humorous remark that the sky really is falling!) That would not be expected if, for example, the cause were extra output from the sun. Yet cooling in the stratosphere is indeed what we see.
"Non-believers don't have to prove anything".
Wrong. This is not a criminal court case, where CO2 is innocent until proven guilty. It's a matter of risk management. The financial cost of making serious strides to reduce emissions is as nothing to that of a 3oC rise in global temperature.
In the last 100 years we have increased the CO2 level way beyond what it had ever been during mankind's previous existence. We are in unknown climatic territory. As with the unleashing of a new drug or food product on the public, the burden of proof is with those doing so.
It is quite true that if Australia is the only country to act it will hardly help at all. But those countries have huge populations. Would it make sense to say that each country should be allowed the same emissions, regardless of population? Of course not! It is the silliest argument of all. It's on a par with "my taxes are less than a millionth of the total, so it doesn't matter if I don't pay them". Why should an individual be entitled to more emissions just because he/she lives in a country with a small population? Ultimately, every country needs to become carbon neutral anyway (or engage in some financial arrangement by which another country draws down what that country emits). The countries which develop and adopt the required technology soonest will then be the best placed economically. Meanwhile, does it make sense for Australia to take a lead? Yes and no. There will short term economic cost in going it alone, but this has to be balanced against the overwhelming need to encourage the others. If each country waits for the others we all lose.
"The CO2 greenhouse effect is already saturated" Some denialists argue that the CO2 in the atmosphere is already having as much greenhouse effect as it can, so adding more won't hurt. That's sort of true if you only look at a fixed height layer of air close to ground level. But what matters is the thickness of the blanket. The effective thickness now is about 5km. From that height, where the temperature is -18oC, it radiates heat into space at the same rate that the sun pours energy in. As you go down through the atmosphere, the air gets warmer at 6.5oC per km. So down here the average is about +14.5oC. More CO2 thickens the blanket, raising the altitude of this -18oC point and increasing the temperature at ground level. The effect on Venus is dramatic: its atmosphere is 96% CO2 and the temperature at the surface is 467oC, hotter even than Mercury. With no greenhouse effect, it has been estimated the temperature there would be below -10oC. Reference: http://www.ccrc.unsw.edu.au/Copenhagen/Copenhagen_Diagnosis_LOW.pdf
In 2007 the IPCC reported that glaciers in the Himalayas could vanish in 30 years. The British Sunday Times claimed that was based on a conversation between a New Scientist journalist and a single Indian scientist a decade ago and was never published as peer-reviewed research. An alternative explanation is that it was a miscopying of the date 2350 as 2035. Either way, the consensus is now that:
How does this affect the GW debate? It ought not affect it much:
But of course, it is fodder for the denialists, so expect an avalanche of criticism for the IPCC. References: http://www.sciencedaily.com/releases/2008/03/080317154235.htm http://www.thegwpf.org/the-observatory/220-himalayan-glacier-melt-timetable-qmistakeq.html
Arctic sea ice extent reached a historical minimum in October 2007, prompting claims that it could be ice-free in summer in 10 or 20 years. In 2008 and 2009, summer extent has recovered somewhat.
Two points must be borne in mind:
Whatever the explanation, sea ice melt will reduce albedo, resulting in more warming. Total melt would threaten the Greenland ice sheet, and if that goes sea levels would rise by metres (but this will take centuries). References: May 2010: http://climateprogress.org/2010/05/13/arctic-ice-volume-nsidc-polar-science-center/ http://www.nasa.gov/topics/earth/features/icesat-20090707.html http://www.metoffice.gov.uk/corporate/pressoffice/2009/pr20091015b.html http://www.time.com/time/health/article/0,8599,1956932,00.html http://www.enn.com/climate/article/41214
The models used to predict the degree of warming assume that relative humidity in the atmosphere (most importantly, the upper troposphere) stays roughly constant. So as the GHGs we add raise the temperature, more water vapour is added. Since water vapour is a strong GHG, this amplifies the effect. Some measurements had cast doubt on this, indicating that the relative humidity is dropping: Theor Appl Climatol, DOI 10.1007/s00704-009-0117-x, Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data Garth Paltridge & Albert Arking & Michael Pook; Received: 21 July 2008 / Accepted: 4 February 2009 The data come from radiosondes, which are sent up on weather balloons. The authors themselves remark "It is accepted that radiosonde-derived humidity data must be treated with great caution". It certainly appeared contradicted by satellite data - see below. Furthermore, it uses "reanalysis". This employs data from different sources at different periods of time. That introduces time-based biases and can appear to show trends which are not there in the individual datasets. (See also Sherwood, S. C., R. Roca, T. M. Weckwerth and N. G. Andronova, Tropospheric water vapor, convection and climate. Reviews of Geophysics, In Press as at Jan 2010.) In January 2010 NOAA researchers reported there was a real and sudden drop in relative humidity of the stratosphere by about 10% around the year 2000. However, stratospheric RH is less important, and the drop was a one-off. Satellite data contradicting a drop in upper-tropospheric relative humidity: Dessler, A. E., Z. Zhang, and P. Yang (2008), Water-vapor climate feedback inferred from climate fluctuations, 2003-2008 Geophys. Res. Lett., 35, L20704 That last includes: "Although an international network of weather balloons has carried water vapor sensors for more than half a century, changes in instrumentation and poor calibration make such sensors unsuitable for detecting trends in upper tropospheric water vapor."
Some denialists claim that the IPCC is assuming CO2 levels in the atmosphere will rise exponentially, whereas observations show a straight line.
It has even been claimed that the CO2 concentration has not risen in 160 years! This seems to be from a misunderstanding of a finding that the fraction of emissions that stays in the atmosphere has not changed in that time.
Graphs have been published purporting to show that the MWP was warmer than today. Much is made of the presence then of a wine industry in England. The MWP was a local phenomenon, occurring only in the northern hemisphere, and in different places at different times. See also It's the Sun. Taking the whole Earth's temperature, from the best available evidence, removes much of the blip. Often, the graph also excludes today's temperature by stopping around the year 1900. For a more complete graph see http://en.wikipedia.org/wiki/Medieval_Warm_Period Even if they're overstated, the Roman and Medieval Warm Periods do indicate that the climate can go through significant swings. So the next step is to look into the cause. The RWP and MWP may well be explained by the high level of volcanic activity then, but for today's warming the only serious explanation is greenhouse gases. As for the wine, there are now more English vineyards than ever.
Researchers have found that volcanoes have been erupting on the Arctic seafloor over the last decade. What effect might this be having on sea ice? Seafloor vulcanism in the Arctic is not new. What's new here is that it was explosive, like a land volcano. This would have been caused by unusually high levels of volatiles and was not necessarily unusually energetic. Either way, the amount of heat involved is tiny compared with the observed ice melt. Reference: http://nsidc.org/arcticseaicenews/faq.html#volcanoes
Climate scientists predicted that GW will not increase the number of cyclones, but will make some stronger. In February 2010, scientists at the US National Hurricane Center reported modelling showing that while the worst will indeed be more violent, they will be fewer in number. Reference: http://www.nature.com/ngeo/journal/v3/n3/pdf/ngeo779.pdf
Denialists point out that water vapour is responsible for 90% of the Earth's greenhouse effect, while CO2 is only responsible for 4%. This is true at a very simple level, but overlooks the dynamics. If the CO2 increases then the temperature rises a little, but that puts more water vapour into the atmosphere, which boosts the temperature much more than the CO2 increase alone did. That is exactly why increased CO2 is so dangerous. If it were not for this amplification there would not be a warming problem (but there would still be the problem of too much CO2 in the oceans). And there's nothing we can do to reduce the water vapour directly. We live on a wet planet, and the amount of water vapour will always be determined by the temperature.
Only 3.4% of CO2 Anthropogenic Some denialists claim that only 3.4% of atmospheric CO2 is man-made. The proportion of CO2 in the atmosphere has risen from 280ppm to 390ppm since the start of the industrial revolution, and some of it would have been anthropogenic before that. So that's at least 28% and rising. Maybe they mean only 3.4% of the annual emissions to the atmosphere are anthropogenic, but that's irrelevant. The non-anthropogenic portion is all part of a long established cycle of emission and absorption. If we add 3.4% to the emissions, some of that will be reabsorbed, but the rest accumulates. It's the accumulation that hurts. Go on long enough and most of what's in the atmosphere will be anthropogenic.
Science is by proof, not consensus It has been argued that science is not a democracy. Here, it is put well:
What the argument glosses over is that falsification only disproves, it doesn't prove. Scientists and philosophers mostly accept that no theory (outside the pure reasoning of mathematics) can be proved in any absolute sense. So how do we acquire new scientific knowledge? When the substantial majority of qualified scientists accept that adequate attempts to disprove various alternative theories have left one as the winner, we have consensus. Various ways have been suggested in which changes in the Sun could affect climate.
So there is no good reason to suppose that the Sun's changes are responsible for an overall warming. But there is evidence that it shifts weather patterns, resulting in a large redistribution of the heat. In particular, shifts in the jet stream can produce cold winters in Europe.
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