'Without very significant action, temperature changes of at least 2°C, and possibly 3°C or 4°C are expected to happen by the end of this century.'
Why would anyone believe this? The first, and most superficial, reason is that most of us rely on newspapers, magazines, and TV for information on climate. We have recently been faced with scary stories about global warming, later modified to the general-purpose, timeless, and incontrovertible 'climate change'. This sleight of hand allowed whatever natural disasters took place (floods, blizzards, hurricanes, etc) to be blamed on fossil fuels, while still retaining the same underlying threat of scary hotness to come.
This is not new. It is merely the media exercising its preference for bad news over good.
Here are some media nuggets from the past, alongside the temperature trends for the time:
1) Cooling: approx. 1885 - 1915.
'Prof. Schmidt Warns Us of an Encroaching Ice Age.' New York Times, October, 1912.
2) Warming: approx. 1915 - 1945.
'Next Great Deluge Forecast by Science: Melting Polar Ice Caps to Raise the Level of the Seas and Flood the Continents.' New York Times, 15 May, 1932.
3) Cooling: approx. 1945 - 1975.
'The threat of a new ice age must now stand alongside nuclear war as a likely source of wholesale death and misery for mankind.' Nigel Calder, International Wildlife Magazine, 1975.
4) Warming: approx. 1975 - 2005.
'Scientists no longer doubt that global warming is happening, and almost nobody questions the fact that humans are at least partly responsible.' Time Magazine, 09 April, 2001.
5) Cooling next? The headlines have already started:
'The Mini Ice Age Starts Here: The bitter winter afflicting much of the Northern Hemisphere is only the start of a global trend towards cooler weather that is likely to last for 20 or 30 years, say some of the world’s most eminent climate scientists.' Daily Mail, 10 Jan, 2010.
Sources for the media quotes: (2), (3), and (4). Useful essay on the media and climate here: (5).
How can we get these short-term trends into perspective?
At any time at any location on the planet, it will either be warming on average or cooling on average, depending on the period of time and/or the spatial area the averaging is taken over. Average your temperatures over a few years, and you have one trend, average over a few hundred years, you have another, over a few thousand, another still. So it is a messy business. And to make matters worse, we have no temperature records at all except for the most recent centuries. A lack of thermometers, and earlier still, a lack of humans, over most of the life of the planet means that we guess at past temperatures using proxies, such as tree-rings (since one of many things influencing tree growth is temperature), isotope ratios in ice cores (since this ratio depends on the air temperature at the time of capture), and numerous other items such as fossils or pollen found in earth cores (since it may be possible to tie some of them to temperature bounds). Ancient documents and carvings permit speculation about harvest times, and major weather-related events such as floods and droughts. Archeological digs reveal details about diets and buildings, and geological explorations reveal previous sea levels, and the movements of continents.
On the really big picture, covering millions of years, we know (or think we do) that the planet was mostly ice-free at the poles. The relatively short periods when there are 'permanent' icecaps are known as Ice Ages. We are in one right now.
During Ice Ages, which can last many hundreds of thousands of years, there are warm spells known as Interglacial Periods, or just Interglacials. These are shown as the purple blips in this temperature reconstruction from ice cores, spanning more than 400,000 years:
During these interglacials, the ice cover disappears every summer in the temperature zones, such as most of North America, and Northern Europe. We humans thrive in such areas during interglacials, since we can grow crops, and not be displaced by inconvenient ice sheets. There is some evidence that the previous interglacial was warmer than our one (7).
Let us now home-in on the last 5,000 years:
We can see that on this big picture, we are in a cooling trend in what may well be near the end of our interglacial period. Superimposed on this trend, are many appreciable excursions, many of which are associated with clear effects on human settlements and civilisations.
Now let us home in on the past 1000 years or so.
The global Medieval Warm Period and the Little Ice Age are shown clearly on the temperature reconstruction using by the IPCC in 1990-2001. There are hundreds of studies of the Medieval Warm Period showing up in many places across the globe - see Jo Nova's report here (9). However, it was not politically convenient for the IPCC to have such a period warmer than our own. In 2001-2003, they replaced it with the infamous 'hockey-stick' plot also shown in the diagram below, in blue. The dismal story of how this artefact was created and jealously guarded for years, is vividly told in Montford's book, The Hockey Stick Illusion (10). It is not an edifying tale, but it is well worth reading for insight into the unscientific attitudes and methods of the small core of alarmists whose temperature reconstructions were so gratefully adopted by the IPCC.
We have been on a gentle warming trend pulling out of the Little Ice Age in the 19th and 20th centuries at overall rates of around 0.6 to 0.7C per century in estimated global average temperature, with shorter-term periods of more rapid warming, or of cooling, superimposed in approximately 30-year long spells. These can be seen on the next graphic, constructed using Hadley Centre data (12) to demonstrate the striking similarity in warming/cooling cycles in the 19th and 20th centuries, despite, of course, the large differences in ambient CO2 levels between them.
But what of real temperatures, as opposed to reconstructions or constructed 'global averages'? The longest temperature record using thermometers is the Central England Temperature (CET) set, which extends back to the 17th century. The Czech physicist Lubos Motl has stepped through this set year by year, calculating the overall temperature trend for the previous 30 years at each step (13). He found nothing unusual about these trends in the 20th century:
'In the late 17th and early 18th century, there was clearly a much longer period when the 30-year trends were higher than the recent ones. There is nothing exceptional about the recent era. Because I don't want to waste time with the creation of confusing descriptions of the x-axis, let me list the ten 30-year intervals with the fastest warming trends:
1691 - 1720, 5.039 °C/century 1978 - 2007, 5.038 °C/century 1977 - 2006, 4.95 °C/century
1690 - 1719, 4.754 °C/century 1979 - 2008, 4.705 °C/century 1688 - 1717, 4.7 °C/century
1692 - 1721, 4.642 °C/century 1694 - 1723, 4.524 °C/century 1689 - 1718, 4.446 °C/century
1687 - 1716, 4.333 °C/century
You see, the early 18th century actually wins: even when you calculate the trends over the "sufficient" 30 years, the trend was faster than it is in the most recent 30 years. By the way, the most recent 1980-2009 tri-decade didn't get to the top 10 results at all; if you care, it was at the 13th place. You can also see that the local trends are substantially faster than the global trends: that's because the global variations are reduced by the averaging over the globe. '
This helps confirm that nothing at all unusual has been observed in temperatures in modern times. Nothing unusual. Nothing untoward. Nothing to get alarmed about. The same is true of other climate measures such as rainfall, storm intensities and frequencies, sea surface temperatures, and polar ice fluctuations. The alarms of the alarmists are going off only in their computers, and not in the world outside.
So what can we say about the future? If we naively project the cooling/warming cycles alone, we can expect a cooling phase for the next 20 to 30 years or so, superimposed on a continuing slow warming, as shown in this diagram:
So where do the forecasts of 2C or more rises (some say 8C or more) come from? They come from computer models within which CO2 is given a more dramatic role by the insertion of a positive feedback parameter to amplify its effects (a feedback not observed in practice, and not even plausible given the relative stability of our climate on the big scale despite major disturbances such as solar dimming, and, incidentally, periods of far far higher ambient levels of CO2). This imagined feedback is needed to produce alarm, since it is widely accepted that CO2 on its own has only a very modest effect, say a few tenths of a degree rise from a doubling of CO2 levels [see Update at foot of this post]. Others of course dispute whether this is even credible, since the so-called 'greenhouse effect' is neither important nor required to explain why greenhouses get hot. It is a totally inappropriate phrase that deserves to be discarded. Other physicists have posited that increasing CO2 will actually tend to cause a modest reduction in temperatures by changing the density of the atmosphere, an atmosphere in which compression and expansion of air are important determinants of temperature. For some recent criticisms of the naive greenhouse theory promoted as gospel by the IPCC, see (15) to (22) incl. A review of climate forecasts from several sources is given here: (23).
What of the immediate future? The reality is we do not know what the temperatures will be at the end of the 21st century. This is currently way beyond our forecasting skills. We can only speculate, and in so speculating, a certain 'modest stillness and humility' would be in order. Not the tiger-like roars we have had to endure from the loudhailers of the IPCC. We would also benefit from further increases in ambient CO2 levels, since they would make possible a substantial increase in agricultural productivity. Overall, on the shaky grounds of past performance, we can 'expect' a temperature change by the end of the century of about 1C. Most people would be better off with a continued gentle warming, and if CO2 levels continue to grow, we'd all benefit from a substantial boost to plant growth rates. All in all, nothing there to get scared about. No need to frighten the children.
But we can be sure climate variation will continue, and it is sensible to review our abilities to cope with a spread in temperatures and other measures of climate. In general, the more wealth, the more advanced low-pollution technologies, and the more robustness to face challenges. One of the most heartening features of the late 20th and early 21st century has been the greater economic freedoms in India and China which have led to a dramatic rise in standards of living where massive poverty had once seemed all but inevitable. They are benefitting greatly from burning coal and oil, just as we did and continue to so do, even as we deploy cleaner sources such as nuclear reactors, and hydro. It seems more than likely that coal-fired power stations will increase in number, and in efficiency, before eventually disappearing as better technologies are developed. We do not benefit from self-hating neuroses about our industrial past and future. Furthermore, we do no good anywhere by transferring these ill-founded climate neuroses on to the next generations. The promotion of facile alarmism into our schools is threatening to depress not only educational standards, but more importantly, the spirits of the young, with lurid tales of a dangerous future due to the very technologies which have brought us so much progress..
Finally, the bit in our 'sentence du jour' about 'very significant action' begs the question of whether we have the first clue about how to direct climate in specific directions, even in principle, and even if so, whether we have the resources to do it.
(1) An apparent group called 'Mothers Against Climate Change' had a website pushing climate alarmism, 'green energy', and carbon trading on to schoolkids and their parents. The site is now defunct, but their statement of reasons why they wanted to get their children worrying about climate is reproduced here: http://climatelessons.blogspot.com/2010/06/schools-low-carbon-day-concerned.html
(2) The NYT quotes from: http://www.saveportland.com/Climate/index.html
(3) More quotes and timelines from 1890 onwards: http://anhonestclimatedebate.wordpress.com/2009/08/02/climate-change-alarmism-timelin/
(5) Overview of journalists and climate variations over the past hundred years or so (' It would be difficult for the media to do a worse job with climate change coverage.'): http://www.businessandmedia.org/specialreports/2006/fireandice/fireandice.asp
(6) Chart showing interglacials in context: http://c3headlines.typepad.com/.a/6a010536b58035970c013480b280e3970c-pi
(7) Comments on paper showing last interglacial warmer than ours in Antarctica ('Unless you are a young Earth creationist, it should be obvious to you that the paper shows that comments that 4 °C or even 2 °C of warming would be threatening for life don't seem compatible with the reconstructions of the climate.'): http://motls.blogspot.com/2010/06/antarctica-4-c-warmer-130000-years-ago.html
(8) Chart showing last 5,000 years or so: http://c3headlines.typepad.com/.a/6a010536b58035970c01310f4ff7a6970c-pi
(9) A useful reference to the hundreds of studies confirming the MWP as being global, along with a critique of the hockey stick ('These maps and graphs make it clear just how brazen the fraud of the Hockey Stick is.'): http://joannenova.com.au/2009/12/fraudulent-hockey-sticks-and-hidden-data/
(10) 'The Hockey Stick Illusion', by A.W. Montford, Stacey International, 2010.
(11) A composite chart showing the infamous hockey-stick plot, and a schematic previously used by the IPCC which more accurately reflects the existence of the MWP: http://wattsupwiththat.com/2010/03/10/when-the-ipcc-disappeared-the-medieval-warm-period/
(12) From the site Global Warming Science: http://www.appinsys.com/GlobalWarming/SixtyYearCycle.htm
(13) Central England Temperatures summarised by warming and cooling spells, with link to CET data: http://motls.blogspot.com/2010/01/warming-trends-in-england-from-1659.html
(14) Future temperatures and IPCC projections, graphic due to Dr Syun Akasofu: http://joannenova.com.au/2009/11/a-simple-proof-that-global-warming-is-not-manmade/
15) Challenging the naive blackbody approach, a paper by Hertzberg, Schreuder and Siddons notes that the Moon, for example, has mass and can store heat. Unlike a blackbody. Linked to here: http://climaterealists.com/index.php?id=5770
(16) A meteorologist asks us to get anthropogenic CO2 into perspective ('The atmospheric greenhouse effect is a flea on the back of an oceanic elephant and the influence of CO2 but a microbe on the back of the flea and the influence of anthropogenic CO2 but a molecule on the back of the microbe.'): http://climaterealists.com/index.php?id=1562
(17) Bootstrapping energy through the magic of re-radiation, and other curiosities discussed here: http://claesjohnson.blogspot.com/
(18) Violating 1st law of thermodynamics: http://climaterealists.com/index.php?id=5903&linkbox=true&position=3
(19) Saturation of radiative role of CO2: http://hockeyschtick.blogspot.com/2010/06/physicist-co2-greenhouse-effect-is.html
(20) CO2 as a response to temperature variations, not a driver of them: http://wattsupwiththat.com/2010/06/09/a-study-the-temperature-rise-has-caused-the-co2-increase-not-the-other-way-around/
(21) Rebuttal of greenhouse effect ('While it is now more-or-less accepted that greenhouses don’t work this way, what isn’t so well known is that neither does the Greenhouse Effect.'): http://www.countingcats.com/?p=4745/
(22)Not in our type of atmosphere ('On a global scale, however, there cannot be any direct water vapor feedback mechanism, working against the total energy balance requirement of the system.'): http://climatology.suite101.com/article.cfm/no-greenhouse-effect-in-semi-transparent-atmospheres
(23) An overview of a selection of temperature projections here ('The CO2 based models appear to be overestimating the amount of warming.'): http://www.appinsys.com/GlobalWarming/GW_TemperatureProjections.htm
Update (30 June 2010). I think my claim that 'since it is widely accepted that CO2 on its own has only a very modest effect, say a few tenths of a degree rise from a doubling of CO2 levels.' is overstating things a bit given the widespread promotion of higher values. I should have said 'around 0.5 to 1.5C' instead to encompass more of the published claims. The broad argument for about 1C without positive feedback, and less than 1C with negative feedbacks is given by Lindzen, e.g. in his recent address to the Heartland conference, and in a Wall Street Journal article last year:
(14a) ('The satellite records of outgoing heat radiation show that the climate is dominated by negative feedbacks and that the response to doubled and even quadrupled CO2 would be minimal.'): http://www.heartland.org/full/24841/Climate_Alarm_What_We_Are_Up_Against_and_What_to_Do.html
(14b) Slightly more technical ( ('You now have some idea of why I think there won't be much warming due to CO2' ): http://wattsupwiththat.com/2010/05/18/dr-richard-lindzens-heartland-2010-keynote-address/
I have also fixed a few typos in the original post.
Note added 7 March 2012. In the 4th last paragraph above I state 'They come from computer models within which CO2 is given a more dramatic role by the insertion of a positive feedback parameter to amplify its effects'. This year I have come across claims in blog comments that this positive feedback is not inserted into these computer models, but rather emerges from them as a result rather than as an input. While I do not find this convincing, I mention it here in case there is real substance to this claim. Since such feedback, and its consequences in the models such as a hotspot in the troposphere, has not actually been observed, this possible lack of a deliberate feedback parameter (or coding) is actually worse news for the plausibility of the models since it would then be a harder flaw to locate and correct.