- Is it Global Warming or Climate Change?
- Do we need to reduce GHG emissions?
- Ocean acidification
- What about the ozone hole?
- What is a sceptic?
- The Disinformation Campaign
- Useful links on the Science
- Popular denialists' arguments and web pages
- Facts and fallacies
- The Psychology of Belief and Denial
- Great video on the history of the science
In 1975, worldwide temperatures had been falling for 20 years, and the concern was that a new ice age was imminent. Dr. Wallace Broecker of Columbia University, a world authority on climate, dismissed it, publishing a paper titled, "Climate Change: Are We on the Brink of a Pronounced Global Warming?" That appears to be the first use of the term Global Warming, and at that time "Climate Change" was only used more generically.
Later, there was a push towards referring to the current problem as "Climate Change" thereby making that a more specific term. This is reported to have come from the fossil fuel lobby, believing it to sound less alarming. But in some ways it is a more accurate term. "GW" gives the impression that everywhere will get a little warmer, which is likely not the case, and fails to draw attention to the most serious consequences. Average temperatures will increase by a few degrees Celsius, but that's a lot less than the annual variations that occur in most places anyway. The local effects of that on climate, though, could be dramatic. Some places will get a lot hotter, some colder, some wetter, some drier, or more or less windy, etc. It may well be beneficial for humans in some regions, such as the far north, but is much more likely to be bad for most people, and to other species that have spent millennia adapting to local conditions.
There are many parts to this question:
- Is global warming happening?
- Can such warming be caused by GHGs (greenhouse gases)?
- Can anthropogenic (emitted by humans) GHGs change the climate significantly?
- Have they done so over the last century?
- How bad will it get if we carry on as now?
- What is a safe level in the atmosphere?
To get a complete measure of the heat in the biosphere you would need temperatures at billions of locations scattered through the atmosphere, land and oceans. You'd also need a good estimate of the total ice at the poles and in glaciers. (If you heat ice that's at 0oC it does not warm up, it melts. Only when it has all melted does the temperature start going up again.)
See "The Complex Business of Measuring Climate Change" http://www.enn.com/climate/article/42296
But there are several ways to spot trends. As well as direct measurents, we can look at ocean levels and changes in plant distributions and animal behaviours. Naturalists observe a shift in the seasons. Ocean levels are rising, which means either they're warming up or land ice is melting and flowing into them, or both.
There can be no doubt the world has warmed in the past 100 years. Some deniers claim it stopped warming around 2000, but that claim is shot down quite easily. Anyone who persists with this argument is a stranger to reason.
In 1896 Svante Arrhenius was thinking about ice ages. He calculated that halving the CO2 in the atmosphere would cool Europe some 4-5°C. Since then, fluctuations in CO2 levels over millions of years have been linked to temperature changes.
But it's not all down to GHGs. "Black carbon" (particles) also trap heat. Jan 2013: Black carbon much more warming than had been thought
Arvid Högbom then calculated that if we were to burn all the fossil fuel available to us it would produce 10 times the CO2 already in the atmosphere. This definitely had the potential to change the climate, but at the rate at the time it would have taken millennia to burn it all. At the current rate of growth it will take a few hundred years, and climate may be affected much sooner.
It is vital to understand that the rate of emissions only affects when it will become a problem, not if. Whether water gushes into a bath or only drips, it will fill it eventually. For this reason, every country needs to aspire to being carbon neutral.
Note that the question is not whether human emissions are the main cause, only whether they have made a significant contribution. Whatever the main cause, if we can mitigate it by reducing emissions then that's what we should do.
Over the years, a vast amount of work has gone into developing models of the climate. These get better all the time. They are assessed by their abilities to "predict" past changes, as known from the geological record, from what is known of the circumstances of those times: atmospheric mix, arrangements of the continents, strength of the sunshine and so forth. None of them are perfect, but increasingly they agree. And most agree that our emissions have been enough to account for the increased GHGs in the atmosphere, and that these in turn are sufficient to have driven the increase.
Nov 2010: 2010 so far tied for hottest year since records began in 1850: http://planetark.org/enviro-
With business as usual, the models predict the temperature will rise several degrees over the next 100 years or so. They indicate that even a 2oC rise is risky. The consensus on the recent Copenhagen accord is that it allows a 3.5oC rise!
Predicting the climate consequences is much harder. Even small long-term changes in temperature can shift winds and ocean currents, leading to quite different patterns of climate. Warmer polar waters could cause a permanent El Niño.
For sea-level rise, the prognosis is clearer. The long-term rise for an extra 1C depends strongly on how much ice is within 1C of melting. Estimates vary from 6 to 20m, but it could take hundreds of years to reach that.
Jan 2011: Canadian Centre for Climate Modelling and Analysis finds warming locked in for 1000 years: http://www.eurekalert.org/pub_releases/2011-01/uoc-cct010611.php
Feb 2011: US Geological Survey finds ancient megadroughts in American Southwest corresponded to temperatures a little above today's: http://planetark.org/enviro-news/item/61298
Sep 2011: Last time it was as warm, sea levels rose to 4-6m higher; Woods Hole: http://www.eurekalert.org/pub_releases/2011-09/whoi-ncd090911.php
What is a safe level in the atmosphere?
At first, the IPCC thought 450-550 ppm was ok, but revised it down to 450ppm. That number seems to have become etched into the minds of many politicians, but meanwhile the scientists have had cause to bring it down to 350ppm. Several propose 300ppm as the completely safe upper limit. The pre-industrial level was about 280, and right now we're approaching 390. If we're already past the safe limit, why aren't we seeing major disasters right now? Because there's a lot of lag in the system. If you increase the level of GHGs in the atmosphere quickly then keep it the same for a while the Earth gets slowly hotter for decades. We've left matters so late that now we don't only need to become carbon neutral but must actually draw down some.
Nov 2010: Atmospheric CO2 38% higher than in 1750: http://planetark.org/enviro-
Unfortunately, we're still not sure how sensitive the temperature is to the GHG level. Existing models say the Earth should have warmed 2oC since pre-industrial times, but it has only warmed 0.8oC. Is this because
- the GHGs are not as powerful as we think, in which case maybe 450ppm is ok,
- the heat is going somewhere we can't observe so easily (more ocean mixing, deep ice warming...), in which case there's more lag in the system, but we still need to act strongly now, or
- pollution haze is blocking the sun, so temperatures will climb rapidly as the air gets cleaner?
Of these, the biggest uncertainties in the science are regarding pollution haze ("aerosols"), so there's no cause for complacency. Another big unknown is how clouds will be affected as the temperature rises further.
Remember 350 ppm!
Oct 2010: 2 deg C "not safe"
Dec 2011: ... or is it 3.1 to 3.9?
May 2013: 1870s naval data confirms ocean warming
Various processes both affect the earth's temperature and are affected by it. So when the temperature changes, the chain of events can lead to another change later on. If the second change is in the same direction as the original one, amplifying it, it is called a positive feedback, otherwise it is a negative feedback. Note that a negative feedback cannot usually result in the temperature going down instead of up; it only makes the increase less.
What matters about a feedback is
- Is it positive or negative, and how strong is it?
- How rapidly does it act?
This can be complicated because a feedback can vary in strength, and even direction, according to circumstances.
Here are some known feedbacks:
- Radiation into space
- Absolute Humidity
- CO2 level
The feedbacks via clouds are a major uncertainty in the science of climate. Depending on the type, timing and location of a cloud, it can warm the earth by acting as a blanket, or cool it by blocking the sun.
Nov 2007: Univ of Alabama; heat-trapping cirrus clouds will decrease: http://www.sciencedaily.com/releases/2007/11/071102152636.htm
Nov 2010: Univ of Hawai'i; a better cloud model implies more warming than thought: http://www.sciencedaily.com/
Dec 2010: Texas A&M Uni; Warming due to increases in greenhouse gases will cause clouds to trap more heat: http://www.eurekalert.org/pub_releases/2010-12/tau-ca120910.php (This study looked at how short-term changes in temperature resulting from ENSO affect clouds. It is unclear whether the same will be true of longer term changes of a more global nature.)
April 2011: US DoE; Effect of clouds on light depends on wavelength: http://www.eurekalert.org/pub_releases/2011-04/dnnl-eoc042211.php
Negative, very strong, immediate. Though perhaps not usually thought of as a feedback, this is the basic mechanism that keeps the earth at a more-or-less constant temperature day-to-day. The hotter the earth, the more heat is radiated into space.
Positive, strong, short term. When the temperature rises, more water evaporates into the atmosphere. It may feel drier because the air is less saturated, but in absolute terms there is more water vapour, and this is a very powerful greenhouse gas.
Strong, positive in the medium term. When the temperature rises, CO2 in the atmosphere increases over the following hundreds of years. This is the result of several separate processes, some of which may in themselves be negative.
Also, CO2 is less soluble in warm water
Oceanic organisms may also flourish.
Feb 2011: Antarctic carbon sink grown since 1990: http://www.eurekalert.org/pub_releases/2011-02/cp-csa021611.php
Mar 2011: Icebergs boost phytoplankton: http://nsf.gov/news/news_summ.jsp?cntn_id=119058&org=NSF&from=news
June 2011: Forests getting denser: http://www.eurekalert.org/pub_releases/2011-06/ru-hdm060611.php
Aug 2013: Europe's forests taking up less carbon
- +/- CO2 released from soil by microcobes can be more with some warming but less with further warming
- Sea temperature
But much longer term there is a strong negative feedback. A hotter earth has more active weather systems, eroding rocks. The exposed rock absorbs CO2, sequestering it. This process takes millions of years, but is thought to be a vital thermostat keeping the earth habitable over billions of years, even though the sun has gradually warmed to be 30% hotter today.
Nov 2011: Peatland carbon more stable than thought
Positive, strong, short term. A cover of sea ice reflects the sun's rays back into space, keeping the planet cool.
CO2 dissolves less well in warmer water, so continued ocean warming will lead to less absorption of CO2, perhaps even a reversal.
Positive, unknown strength, various timescales. Clathrates are frozen mixtures of methane and water which can lie at the bottom of oceans. Permafrost also retains methane. Warming will melt more of these, releasing the methane into the atmosphere. How much is there and how quickly they will melt is uncertain.
Feb 2011: Up to 2/3 of permafrost likely to disappear by 2200; Uni of Colorado: http://www.colorado.edu/news/r/41e56cf851aed9b1d38ec3dddd7f60b8.html
Nov 2011: Release of gas hydrates may have caused 56myo mass extinction; Rice Uni: http://www.media.rice.edu/media/NewsBot.asp
Feb 20131.5C rise will melt permafrost
June 2013: NASA finds emissions from Arctic thaw scary
Oct 2013: IPCC lifts CH4 warming potential by 20%
Latitudinal air mixing
- Nitrous Oxide
There are signs that more mixing is occurring between arctic air and the northern temperate zone. While this produces cold weather in Europe and North America, it warms the arctic, leading to global warming as described above. If this mixing is caused by the warming then it is another positive feedback path.
Fresh water from melting glaciers and ice caps alter ocean circulation with potentially dramatic effects on climate.
July 2012: Release of N2O may have ended last ice age
Soot from forest fires and industry darkens snow, cutting albedo and helping it melt.
Even if global warming were not an issue, our CO2 emissions are seriously damaging ocean life. Denialists don't usually discuss this because there are far fewer opportunities for sowing doubt. CO2 increases the acidity, making it harder for corals and shellfish to grow, and even dissolving them.
The Carbon Cycles
The natural cycle by which carbon is moved and transformed on Earth can usefully be broken into two parts:
- A fast cycle, moving carbon between organic matter, the atmosphere and the oceans
- A slow cycle, moving carbon between the fast cycle and geological deposits
For a complete diagram see http://en.wikipedia.org/wiki/Carbon_cycle
Burning fossil fuels results in a much faster movement from the geological deposits into the fast cycle. As the quantity of carbon in the fast cycle increases, that will gradually raise the rate at which carbon is moved back out of the fast cycle, but it will take thousands of years for a new balance to be established. More carbon in the fast cycle will tend to mean more carbon at all stages within it, and that includes the CO2 in the atmosphere.
The loss of ozone in turn affects climate: http://www.bbc.co.uk/news/science-environment-13161265
Jan 2012: Arctic ozone hole at worst yet: http://www.kit.edu/visit/pi_2012_8751.php
Climate Change deniers prefer to be called sceptics. A sceptic, though, is someone who believes something only when the evidence for it outweighs the evidence against. All scientists worthy of the term are sceptics by definition, and the majority of climate scientists are persuaded of anthropogenic (human-induced) global warming. For most deniers the scepticism is entirely one-sided, not being sceptical for a moment about their own position.
Certainly there are some serious scientists who doubt AGW, and these must be given due consideration. It has been noted that they tend to be retired or approaching retirement. Eminent physicist Max Planck observed, "a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up." Or as some have it, "science advances one funeral at a time."
Meanwhile, major policy decisions cannot wait for unanimous agreement. Politicians must judge the consensus. This analysis should help: http://www.pnas.org/content/early/2010/06/04/1003187107.abstract.
Debunking various climate change deniers:Sandi Keane on the Institute of Public Affairs
Dave Rado on Martin Durkin's film, the Great Global Warming Swindle.
General discussions on denialism:
Bush's advisors as lobbyists for the carbon mafia
Jun 2013: Leaked memos betray campaign of doubt...
Fox News managing editor instructs staff to cast doubt on global warming: http://mediamatters.org/blog/201012150004
On the mismatch between scientific consensus and public impression: http://www.climatecentral.org/blog/are-scientists-confusing-the-public-about-global-warming/
Feb 2012: How US denialist group and Big Oil fund denialism in Oz: http://climatespectator.us1.list-manage1.com/track/click?u=3965871af52170b27860e0c8a&id=e10a3ed238&e=85faf75e25
May 2010 : Three reports from the US National Research Council
August 2010: Australian Acacdemy of Science Q&A
June 2011: CSIRO's eBook on climate change
June 2011: CSIRO's CO2 rise tracker
June 2011: ESA's Arctic sea ice thickness map
Sep 2011: On the use of models
A history of the science http://www.aip.org/history/climate/co2.htm
Good recent updates http://www.copenhagendiagnosis.org/, and http://www.parliament.vic.gov.au/research/2009CIClimateChange.pdf
The scientists write: http://www.ucsusa.org/global_warming
Climate simulation using C-ROADS
Earth - The Power of the Planet (BBC DVD, 2007)
Oct 2010: Obama science advisor
The Gulf Stream is part of the Atlantic Meridional Overturning Circulation (AMOC), an ocean circulation system that carries warm upper waters north and returns cold, deep water south. This process is also known as the North Atlantic thermo-haline circulation.
Yes, GW could shut down the Gulf Stream, and yes, that might make temperatures a few degrees cooler in Western Europe than GW would otherwise have made them. But stopping the Gulf Stream will not cause an Ice Age. Most of the winter temperature difference between Eastern seaboard US and Western seaboard Europe is caused by the prevailing winds being West to East. The Atlantic ocean acts as a huge heat buffer, tending to smooth out the year-round temperatures, and the Westerly winds transport this smoothing to Europe. The Gulf Stream helps, but is not the major component.
But GW could change the wind patterns in ways that are hard to predict.
Nov 2010: Northern winters may get colder; Potsdam Institute for Climate Impact Research: http://www.sciencedaily.com/
Apr 2011: Leakage of Agulhas current from Indian Ocean to Atlantic could help maintain the AMOC and keep Europe warm; US NSF: http://nsf.gov/news/news_summ.jsp?cntn_id=119293&org=NSF&from=news
First, there have not been more earthquakes and volcanoes than normal in recent years. Secondly, it would be very hard to relate any given such event to global warming.
That said, GW could affect seismic activity. Melting of thick ice cover could release magma; conversely, rising sea levels could mean fewer eruptions from coastal volcanoes; changing wind patterns alter the ocean's pressure footprint on the crust, triggering earthquakes and tsunamis.
Research by the National Oceanography Centre, Southampton, UK, into weather variations during the Cretaceous warm period indicates that these decadal cycles occurred at about the same frequency as today.
Oct 2011: GW making El Ninos more severe
While CO2 is the one most discussed, other emissions can be significant. See the IPCC's GHG list for details. How much each contributes is complex. The relative importance can change over time. Methane slowly converts to CO2, which is a less powerful GHG. For convenience, formulas have been standardised for expressing all such emissions in tCO2e (tonnes of CO2 equivalent).
Soot particles ("black carbon") are also important.
Aug 2011: Two possibilities for why methane increase stopped in the 1980s: http://www.eurekalert.org/pub_releases/2011-08/uoc--usf080511.php
The Psychology of Belief and Denial
US public greatly underestimates the level of scientific consensus:
How denialists turn noise into pauses:
Many have become intrigued by the phenomenon of climate change denial. Social scientists have found strong correlations between political hue and a general tendency to reject bad news. Their studies could help frame the AGW message more effectively.
May 2011: Belief unduly influenced by weather this instant; Columbia Business School:http://www.eurekalert.org/pub_releases/2011-05/cbs-sfl052711.php
April 2011: Uni of NH: Those most confident of understanding issues are the most split along political lines:http://www.eurekalert.org/pub_releases/2011-04/uonh-uci041911.php
April 2011: Uni of Michigan: political divide deepens:http://www.enn.com/pollution/article/42600
April 2011:Uni of Michigan:http://green.blogs.nytimes.com/2011/04/09/taking-on-climate-skepticism-as-a-field-of-study/
April 2011: Daily weather affects belief in climate change; Columbia Uni:http://www.earth.columbia.edu/articles/view/2794
April 2011: "Greenhouse 2011" conference in Cairns: http://www.newscientist.com/blogs/shortsharpscience/2011/04/are-climate-change-sceptics-ju.html
Mar 2011: Research on climate change communication:http://www.eurekalert.org/pub_releases/2011-03/cu-awr033111.php
Jan 2011: Merseyside Skeptics meeting:http://liverpoolcafescientifique.org/climate-skeptics-climate-and-holocaust-denial-how-do-we-change-minds
Jan 2011: Dire warnings counterproductive:http://www.nature.com/news/2011/110104/full/news.2011.701.html
Jan 2011: George Marshall's video:http://climatedenial.org/
Sep 2010: ABC RN's All In The Mind:http://www.abc.net.au/rn/allinthemind/stories/2010/2998311.htm
Dec 2009: The Psychology of Climate Change Denial:http://www.wired.com/wiredscience/2009/12/climate-psychology/
Dec 2009: AGW message viewed as "revenge of the nerds":http://www.opendemocracy.net/ourkingdom/brian-davey/mass-psychology-of-climate-change-scientists-need-attitude
March 2009: Bristol conference http://www.guardian.co.uk/environment/cif-green/2009/mar/09/denial-climate-change-psychology
Nov 2011: The Hierarchical-individualistic versus the Egalitarian-communitarian: http://theconversation.edu.au/why-do-people-reject-science-heres-why-4050
Nov 2011: Report on public risk perceptions, understanding, and responses in Australia and UK: http://apo.org.au/research/public-risk-perceptions-understandings-and-responses-climate-change-australia-and-great-bri
Political stance has also been related to neurological differences in areas affecting threat response:
April 2009: Brain structure differences between liberals and conservatives:http://news.yahoo.com/s/afp/healthpoliticsusbritain
The Australian Psychological Society has a help page on coming to terms with environmental threats:http://www.psychology.org.au/publications/tip_sheets/climate/
Jan 2012: The Debunkers Handbook