Is it Global Warming or Climate Change?

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.

Broecker was not the first.  Several researchers in the early 70's made remarkably accurate predictions of what would come to pass by 2000

Do we need to reduce GHG emissions?

There are many parts to this question:

Is global warming happening?

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"

But there are several ways to spot trends.  As well as direct measurements, 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.

Perhaps the strongest evidence for continued global heating is the radiation imbalance.  Satellites show there is more energy coming into the Earth from solar radiation than the Earth is radiating back out.  That excess energy is being stored somewhere.

Oct 2011Erstwhile sceptic Prof Muller declares GW real

Oct 2013: 21st century slowdown in warming may be due to background oscillation

Dec 2014: Link to extreme weather events can now be made

Can such warming be caused by GHGs (greenhouse gases)?

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

Apr 2013: Major study shows gradual cooling for 2000 years was reversed by industrial revolution
Feb 2016: Statistical correlation nails GHGs

Can anthropogenic GHGs warm the planet significantly?

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.

Nov 2012: Tropospheric and Stratospheric measurements finger human activity

Have they warmed it significantly over the last century?

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:

Aug 2012: American Meteorological Society's 2012 report

Apr 2016: Humans responsible for nearly all warming since 1950s 

How bad will it get if we carry on as now?

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.

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 6m 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:

Feb 2011: US Geological Survey finds ancient megadroughts in American Southwest corresponded to temperatures a little above today's:

Sep 2011: Last time it was as warm, sea levels rose to 4-6m higher; Woods Hole:

Nov 2012: Stalactite study shows rise likely limited to 1m/century, in line with most current models

Aug 2013: Geologic record shows Antarctic melt can raise seas 5m in under a millennium

Jan 2014: Vertical mixing of air  stronger than thought, increasing climate sensitivity

Dec 2014: Equation expresses relationship between GHGs and warming

Jan 2015: Plankton study confirms 1.5-4.5 sensitivity range

Apr 2015: Burning all fossil fuel would raise temperature 16C

Apr 2016: Significant impact differences between 1.5C warming and 2C 

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 (2010) we're approaching 390If 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:

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. 

May 2011: Less ocean mixing than expected; spotlight shifts to aerosol pollution

Remember 350 ppm!

Oct 2010: 2 deg C "not safe"

Nov 2010: Each GtCO2-e leads to 0.0015 deg C of global warming

Nov 2011: Study puts sensitivity at about 2.4 deg C per CO2 doubling ...

Dec 2011: ... or is it 3.1 to 3.9?

May 2013: Range of future warming narrowed by new research

May 2013:  1870s naval data confirms ocean warming 

Mar 2014: Warming slowdown has led to underestimates of climate sensitivity

May 2014: Pacific hotspot adding to Arctic warming

Does GW threaten humanity's survival?

The most worrying aspect may be the effect on ocean circulation.  Several major extinctions in the geological record have resulted from prolonged vulcanism pumping vast quantities of CO2 into the atmosphere.  The resulting warming is more at the poles than at the equator, reducing the temperature difference.  That takes away the driving force behind the deep sea ocean currents.  Without those, the deep ocean becomes de-oxygenated.  Sulphate-reducing bacteria take over, pumping toxic H2S into the atmosphere.

Has GW stopped?

The pace of warming has certainly slowed since around 2000.  Has  it reached a plateau?  How long will the slowdown last?

A major reason scientists conclude Global Warming is a reality is the 'radiation imbalance'.  Satellites show that more radiant energy is entering the planet than leaving it.  In a steady climate, it should be the other way around; heat generated by nuclear fission within the Earth needs to escape too.

It's much harder to pin down exactly where the heat is going.  There are relatively few measuring stations at the poles, and hardly any before 2000.  The deep ocean is an even greater unknown.  If vertical mixing is only a little more than currently believed then it would account for a great deal of hidden heat.

There have been changes which, together, largely explain the slowdown:


1998 was an unusually strong El Niño year.  Since then, La Niñas have predominated.  As far as is known, this is not a result of GW but of natural variability.

Solar cycle

In the sun's cycle of activity, the current quiet phase has been longer than usual.


The last decade, has been more than usually volcanic.  Sulphate aerosols serve to reflect some of the sun's radiation back into space. 

 In each case, the respite is likely to be temporary.

Jan 2015: World network of sensor buoys proves excess heat going to deeper ocean


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?
  • This can be complicated because a feedback can vary in strength, and even direction, according to circumstances.

  • How rapidly does it act?
Nov 2012: Faster-than-expected rise blamed on feedbacks

Here are some known feedbacks:

April 2011:

July 2012: CO2 rise from warming blamed on Southern Ocean winds

  • -/+ Plant growth is stronger in temperate zones when warmer, taking up CO2.  But too much warming can make it a positive feedback.  One model suggests the response of plants to increased CO2 could trim 15% off a 2 degree warming.

Oceanic organisms may also flourish. 

Feb 2011: Antarctic carbon sink grown since 1990:

Mar 2011: Icebergs boost phytoplankton:

June 2011: Forests getting denser:

July 2013: Tropical forests absorb less CO2 as temperature rises

Aug 2013: Europe's forests taking up less carbon

Jan 2014: Eucalypt forests expected to shrink

Jun 2015: Algal protein to change ocean absorption models 

Positive, long term.  CO2 dissolves less well in warmer water, so continued ocean warming will lead to less absorption of CO2, perhaps even a reversal.

  • Sea pH

Ocean acidification to add up to 0.5C warming this century

  • Methane, Permafrost and Clathrates

  • 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: 

Nov 2011: Release of gas hydrates may have caused 56myo mass extinction; Rice Uni:

Aug 2012Likely to be large methane deposits under Antarctic ice

Oct 2012: Increased CO2 and temperature leads to more methane from agriculture

Feb 20131.5C rise will melt permafrost

May 2013: Carbon in tundra soils more stable than thought

June 2013: NASA finds emissions from Arctic thaw scary

June 2013: Caves show 1.5C warming tipping point for permafrost

Oct 2013: IPCC lifts CH4 warming potential by 20%

Apr 2014: Warming wetlands responsible for methane increase

July 2014: Melting permafrost might not be all bad

Nov 2015: Natural methane emissions rise exponentially with temperature

Ocean Acidification

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.

Jan 2012: Acidification up to 100 times natural rates in geological record

Apr 2014: High CO2 makes fish rash


Dec 2012: Higher CO2 can boost production but at expense of nutritional value

Other factors affecting climate

Many other factors affect climate, but only GHGs come close to explaining the observed trend.  See graphs.

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

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.

What about the ozone hole?

GHGs warm the earth's surface by trapping heat in the lower layers of the atmosphere.  That also means the upper layers get colder.  Unfortunately, the chemical reactions up in the stratosphere by which CFCs destroy ozone happen faster at colder temperatures, so AGW also expands the ozone hole. 

The loss of ozone in turn affects climate:

Jan 2012: Arctic ozone hole at worst yet:


What is a sceptic?

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:



The Disinformation Campaign

Debunking various climate change deniers:

Abraham and Nuccitelli on Richard Lindzen

Amory Lovins on the role of the media

Jon Abraham on Viscount Monckton

Sandi Keane on the Institute of Public Affairs

Tim Lambert's blog 'The Australian's War on Science"

Bob Ward on Prof. Bob Carter at James Cook University

Dave Rado on Martin Durkin's film, the Great Global Warming Swindle.

Howard Friel on Bjørn Lomborg.

Ian Enting on Ian Plimer

Mike Sandiford on Ian Plimer

Barry Brook on Ian Plimer's "Heaven and Earth"

Jon Doig on Leon Ashby's"Why an ETS is not necessary"

Ove Hoegh-Guldberg on The Australian's deceptions over the threat to the Great Barrier Reef.

Michael Ashley on The Australian's readiness to be a platform for denialists

General discussions on denialism: of Denial

Bush's advisors as lobbyists for the carbon mafia

Naomi Oreskes' "Merchants of Doubt" on Radio National : Audio/Transcript

Greenpeace's exposure of denialist funding

Jun 2013: Leaked memos betray campaign of doubt...

... and Australia's media play along

Jan 2011

Fox News managing editor instructs staff to cast doubt on global warming:

On the mismatch between scientific consensus and public impression:

Feb 2012: How US denialist group and Big Oil fund denialism in Oz:

 Useful links on the Science

May 2010 : Three reports from the US National Research Council

Advancing the Science of Climate Change

Limiting the Magnitude of Future Climate Change

 Adapting to the Impacts of Climate Change

August 2010: Australian Acacdemy of Science Q&A

Jan 2011: Big four climate groups agree on temperature record 

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 2011On the use of models

A history of the science

Good recent updates, and 

The scientists write:

Climate simulation using C-ROADS

Earth - The Power of the Planet (BBC DVD, 2007)

Oct 2010: Obama science advisor

Jan 2015: Models get it right, on average

Jan 2015: Prof Chris Rapley's one-man show

Aug 2015: Models predict readings accurately

July 2016Climate models now highly accurate

Oct 2016: Energie Portal (Dutch site, in English) 



Popular denialists' arguments link

Climate Change deniers' websites:

A Cool Look at Global Warming

JoNova's Skeptics Handbook 

Lord Monckton & SPPI 

Climate Sceptic Show 

The Galileo Movement





Miscellaneous facts and fallacies

1. Will GW shut down the Gulf Stream and cause an Ice Age in Europe?

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:

Apr 2011: Leakage of Agulhas current from Indian Ocean to Atlantic could help maintain the AMOC and keep Europe warm; US NSF:

May 2011:

2. Is GW responsible for increased earthquakes and volcanoes?

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.

3. Could GW cause a permanent El Nino or La Nina?

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.

May 2011: Strong ENSOs likely more frequent in warmer world

Oct 2011: GW making El Ninos more severe

4. What are the GHGs?

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. 

It is often stated that methane is a much more potent GHG than CO2.  That's not really true.  In the context of the emissions spectrum from the Earth, and the presence of large amounts of water vapour but little of other GHGs, CO2 is intrinsically about twice as powerful as methane.  But the effect of any given gas declines logarithmically.  Each doubling of the gas concentration increases the absorption by the same amount. 

Although the atmosphere is only about 0.04% CO2, that's far more than for methane. So a small increase in methane level represents a large percentage increase, which means a high GHG potential.

For convenience, formulas have been standardised for expressing all such emissions in tCO2e (tonnes of CO2 equivalent).  Since methane slowly converts to CO2, the equivalence also depends on the timescale considered.

Soot particles ("black carbon") are also important.

Feb 2011:

Aug 2011: Two possibilities for why methane increase stopped in the 1980s:

Sep 2012: Methane stopped rising because of changed mining practices

Dec 2013: New potent and persistent man-made GHG identified

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.

Apr 2017: What brings denialists around 

Apr 2016: Conservatives respond to patriotic appeal 

Apr 2016The Key?: make taking action the new normal 

Apr 2016: Leading denialist shies from wager 

Sep 2015: Audio: Clive Hamilton and Carmen Lawrence on ABC's Big Ideas

June 2015: A practical guide to dealing with denial

Nov 2014: Climate too hard, while clean & green inspires

Nov 2014: Sceptics unswayed by hot winters

Aug 2014: Climate facts can persuade conservatives

July 2014:  "My side bias" beats the facts 

Jun 2013: The open-minded are swayed only by hearing both sides

Dec 2012: Conservatives get environmentalism when expressed as threat to purity

Nov 2011: The Hierarchical-individualistic versus the Egalitarian-communitarian:


Nov 2011: Report on public risk perceptions, understanding, and responses in Australia and UK

Sep 2011: On the joys of not being a climate scientist


May 2011: Belief unduly influenced by weather this instant; Columbia Business School:

May 2011:American Psychologist special issue on environmentalism

April 2011: Uni of NH: Those most confident of understanding issues are the most split along political lines:

Jan 2011: George Marshall's video:

April 2011: Uni of Michigan: political divide deepens:


April 2011:Uni of Michigan:

April 2011: Daily weather affects belief in climate change; Columbia Uni:

April 2011: "Greenhouse 2011" conference in Cairns:

Mar 2011: Research on climate change communication:

Jan 2011: Dire warnings counterproductive:

Sep 2010: ABC RN's All In The Mind:

Dec 2009: The Psychology of Climate Change Denial:

Dec 2009: AGW message viewed as "revenge of the nerds":

March 2009: Bristol conference

Political stance has also been related to neurological differences in areas affecting threat response:

April 2009: Brain structure differences between liberals and conservatives 

The Australian Psychological Society has a help page on coming to terms with environmental threats:

Jan 2012: The Debunkers Handbook

Feb 2012: What drives public opinion on climate change? Study

Aug 2013: How Fox News creates distrust in the science