2011-09-21 11:44:28BLOG EXPERIMENT CONDITION 1: warmist post, warmist comments
John Cook


As the second part of our experiment on science blogging, we'll be showing 4 conditions to lab participants at the Uni of W.A. The condition for this thread is Warmist Blog Post, Warmist Comments. So would be great if a handful of SkSers could post glowing, very warmist comments to our "How we know..." blog post - posted here in this forum thread. We need exactly 10 warmist comments. If you need to nitpick any element of the post (I'm looking at you, Chris Colose), do so in the Warmist Blog Post, Skeptic Comments condition.

How we know we're causing global warming in a single graphic

Posted on 27 July 2011 by John Cook

In 1859, physicist John Tyndall ran an experiment demonstrating the greenhouse effect. Visible sunlight easily passes through our atmosphere to warm the Earth. However, invisible heat rays rising from the Earth’s surface, otherwise known as infrared radiation, don’t easily escape back to space. What Tyndall showed by shining heat rays through tubes filled with different gases is that certain gases like water vapour and carbon dioxide block the heat rays. These became known as greenhouse gases.

Tyndall also made several predictions of what we should expect to see if greenhouse gases were causing warming (Tyndall 1861). In fact, we expect to see a number of distinctive greenhouse patterns in global warming. Observing these patterns strengthens the evidence that humans are causing global warming, as well as eliminates other possible natural causes. Let's have a look at the many human fingerprints on climate change:

How we know we're causing global warming

Humans are raising CO2 levels

The first point to establish is that humans are the cause of the rise in atmospheric CO2 levels. This fact is common sense. The amount of CO2 in the atmosphere is going up by around 15 billion tonnes per year. Humans are emitting around twice that much! On top of this, there are a number of lines of evidence to confirm that we're the cause of rising CO2 levels.

When we measure the type of carbon accumulating in the atmosphere, we observe more of the type of carbon that comes from fossil fuels (Manning 2006). As you burn fossil fuels, you take oxygen out of the atmosphere. Measured oxygen levels are falling in line with the amount of carbon dioxide rising (Manning 2006). There's been a sharp rise in "fossil fuel carbon" in corals (Pelejero 2005) and sea sponges (Swart 2010). Anthropogenic CO2 is penetrating even to the ocean depths (Murata 2010). Measurements of radiocarbon in tree-rings confirms human activity is the cause of rising CO2 (Levin 2000). Even the pages of ancient books trace the rising effects of fossil fuel pollution going back to beginnings of the industrial revolution (Yakir 2011).

So many independent lines of evidence (and common sense) confirm that yes, we are responsible for the recent rise in atmospheric CO2.

The extra CO2 is trapping heat

Our understanding of the greenhouse effect provides a number of verifiable predictions. If carbon dioxide is trapping more heat, we should see less heat escaping to space. Satellites measuring infrared radiation coming from Earth find less heat escaping to space over the last few decades, at those exact wavelengths that carbon dioxide absorbs energy (Harries 2001Griggs 2004Chen 2007). The researchers who analysed this data described this as:

"...direct experimental evidence for a significant increase in the Earth's greenhouse effect".
Harries 2001

If less heat is escaping to space, there's only one place it can go - back to the Earth's surface. Scientists check this by measuring infrared heat coming down from the atmosphere. These measurements confirmed the satellite data - more heat is returning to the Earth's surface (Philipona 2004Evans 2006Wang 2009). This extra piece of evidence upon the existing body of evidence led scientists to conclude that:

"This experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming."
Evans 2006

Unfortunately the scientists underestimated the human capacity to ignore  evidence staring us in the face.

Global warming has a distinct greenhouse signature

As far back as the mid 1800s, Tyndall predicted that greenhouse warming should cause nights to warm faster than days. This is because at night, the Earth's surface cools by radiating heat out to space. Greenhouse gases trap some of this heat, slowing the night-time cooling. It took over 130 years before Tyndall's prediction was confirmed. Over the last few decades, surface measurements have observed nights warming faster than days (Braganza 2004Alexander 2006,Zhou 2009).

Tyndall made another prediction of what greenhouse warming should look like. Just as greenhouse gases slow down nighttime cooling, they also slow down winter cooling. So Tyndall anticipatedwinters warming faster than summers. Again, recent analysis of temperature trends over the last few decades bear this out (Braganza et al 2003Braganza et al 2004). Both thermometers and satellites find winters warming faster than summers.

And the evidence continues to build. Another distinctive greenhouse pattern can be found in the atmosphere. With heat being trapped, we expect to see the lower atmosphere to warm. But with less heat escaping to space and more carbon dioxide in the stratosphere, we also expect to see the upper atmosphere cool. Satellites and weather balloons both observe this curious contrast between upper cooling and lower warming (Jones 2003).

With the lower atmosphere (the troposphere) warming and the upper atmosphere (the stratosphere) cooling, the boundary between the troposphere and stratosphere, otherwise known as the tropopause, should rise as a consequence of greenhouse warming. This has been observed (Santer 2003). An even higher layer of the atmosphere, the ionosphere, is expected to cool and contract in response to greenhouse warming. Satellites measure this effect (Laštovika 2006). We are changing the very structure of our atmosphere.

What's fascinating about all these greenhouse signatures is they also rule out a number of other potential causes of global warming. If the sun was causing global warming, it would cause summers to warm faster than winter, days to warm faster than nights and the upper atmosphere to warm. Observations rule out the sun.

Similarly, the pattern of ocean warming rules out ocean cycles as the driver of global warming. The world’s oceans have been building up heat over the past half century. This isn't a case of heat shifting around due to ocean cycles but the entire global ocean system building up heat. The specific pattern of ocean warming, with heat penetrating from the surface, can only be explained by greenhouse warming (Barnett 2005).

If it walks like a duck and quacks like a duck...

Current global warming shows all the distinctive signatures of greenhouse warming. To be skeptical that humans are causing global warming, you must believe two things. Something unknown is causing warming that happens to mirror the greenhouse effect. And something unknown is somehow suppressing the well understood (and well observed) greenhouse effect. So we can accept what we know to be true (greenhouse warming) or we accept two unknowns.

The saying goes if it walks like a duck and quacks like a duck, then it must be a duck. But climate skeptics are trying to convince us it's some other, undefined animal impersonating a duck that's also mysteriously hiding the real duck.

2011-09-22 00:30:04


Yes - climate change is happening and we are causing it.  It isn't rocket science.

How we know that climate change is happening, apart from the satellite data, is that these observations can all be - and have been - replicated by amateur scientists.  Even the relatively 'hard' science of CO2 absorption has been tackled by amateurs.  All you need is an astronomical telescope and a spectrometer and you too can see the absorption spectrum of CO2.  Or you can rely on direct observation with the proverbial 'Mark 1 eyeball'.  I live in a coastal region.  With no exceptions, all the places I played in as a child back in the 1950s have had their sea defences raised - in many case three times.  Spring buds are seen earlier; leaves fall later.  I know from first hand experience that the climate here is changing.  I have no reason to disbelieve older people from other regions and countries who similarly report changed climates in their lifetimes.

How do I know that we are causing it?  I don't.  But I do know that we have exhausted many sources of coal, oil and gas.  I also know that we keep adding area to our roads and cities.  This reduces the area capable of absorbing CO2 and adds CO2 from the manufacture of cement.  We have used up most of the high grade metal ores and are now using carbonates.  Reducing carbonates to metals puts vast amounts of CO2 into the atmosphere.  We are making vast reductions of green spaces and we are dumping great quantities of CO2 and other gases into the atmosphere.  The suggestion that this is not causing the climate change that I have observed in my lifetime is far beyond the realms of rational thinking, to put it as kindly as I can.

2011-09-22 05:15:40
Steve Brown


If anyone is interested in more info on john Tyndall and how the evidence grew from the mid-19th century I can thoroughly recommend this book which is a free download: The Discovery of Global Warming by Spencer Weart.


Great post!

2011-09-23 13:11:42Pieces in a jigsaw puzzle.
Glenn Tamblyn


Skeptics often think the the theory of Global Warming is like a house of cards - pull one card out and it all falls down. Actually it is more like a jigsaw puzzle. Lots of pieces that all fit together. Most of the pieces are in place but occassionally we aren't sure about where one piece should go. And we can see most of the detail of our puzzle - looks like a farming scene. If one piece doesn't look quite right does that mean we have it all wrong and the jigsaw is actually of a scyscraper? No. It just means we aren't quite sure about this piece yet.

Climate Science is made of so many parts that all support each other. Physics predicts what GH gases will do in the atmosphere which says we should see changes in the pattern of radiation going to space, which we do. It then predicts that the structure of the atmosphere will change, which we see. Since the GH Effect operates 24/7 we should see changes at night as well as during the day - ditto. Then most warming will go into the oceans because it takes massively more heat to warm them. And so on... Since it is our CO2, we should see the chemistry of the type of CO2 we are releasing reflected in places where this CO2 can go - Oceans, Corals, Trees etc.

The pieces all fit together pretty well. And I think most of us can tell the difference between a jigsaw puzzle and a house of cards. So why can't they? Why does admitting this is true frighten them so much?

2011-09-24 21:41:04


A picture says more than a thousand words, doesn't it? Thanks for the neat graphic highlighting some of the important fingerprints showing that, yes, indeed humans are causing global warming. we may not yet know all the nitty gritty details of how and why things work as they do, but we most certainly know more than enough to get our act together and reduce our carbon emissions ASAP.

2011-09-25 12:17:20
Dana Nuccitelli

That is a great graphic, showing all the 'fingerprints' of man-made global warming.  A key 'fingerprint' is the cooling upper atmosphere, as the Earth's lower atmosphere and surface warm.  There aren't a lot of ways to explain why the upper atmosphere would be cooling, other than an increased greenhouse effect trapping heat in the lower atmosphere.  Increased solar activity would make all layers of the atmosphere warm, for example.  Great graphic, and great summary of the evidence for man-made global warming.

2011-09-26 04:32:25
Alex C


One other indicator of humans increasing CO2 as opposed to the oceans being a source is that oceanic acidification at the surface is occurring, and at lesser rates as you go down.  If the oceans were net giving up CO2 instead of taking it in, we would expect pH to go up since CO2 is an acid.  As CO2 increases, it leads to a decrease in pH, which we are observing.  So, it's not just that the isotopic ratios of 13C/12C and 14C/12C are decreasing, the idea of oceans supplying CO2 is incompatible just with the fact that CO2 is accumulating in them!

Excellent summary, and especially list of references.  If only people would read the science more, there is a lot of fascinating material to learn.  I remember disucssing global warming with a friend of mine, he said that he has yet to see much scientific evidence for them (and said the issue is becoming too political - which I agree with to an extent).  I brought up the Suess Effect - the CO2 ratio effect you mentioned - and he said that he hadn't heard of that before, and thought that if the science could be better communicated then people would take the issue more serisouly.  I think this is a great start to doing just that.

2011-09-26 13:28:09


Ocean acidification is a strong sign that humans are raising CO2 levels. But it's also a grave environmental concern as the acidification is causing damage to coral reefs which are some of the most diverse ecosystems on the planet. Adding insult to injury, the increased CO2 causes warming which is causing further damage to the coral reefs through bleaching. Corals provide both evidence for man-made global warming and concern over its impacts.

2011-09-26 14:07:17
Glenn Tamblyn


Good points about ocean acidification. ANd the impacts aren't just restricted to coral reefs. There are a range of small and microscopic creatures throughout the open ocean that will also be badly affected by the impact of acidification on their ability to maintain Clacium Carbonate shells. Corals are a great source of biodiversity and are often spawning grounds for many fish, but the open ocean is where most of the life in the oceans is located. And the small creatures out there are the basis of the entire marine food chain. Acidification combined with overfishing could devastate that food chain.  We may have stopped hunting whales to extinction but we could well starve them to it.

A couple of interesting things I came across recently. When you look at rocks in the ocean, above a certain depth, typically 1000 metres, they are often light and white colours. This is because they contain lots of Calcium Carbonnate - limestone etc. Below that they are dark brown colours. No more Calcium Carbonate. At that depth the calcioum carbonate can't exists - it dissolves into the seawater. Ocean Acidification means that this critical depth is rising, up towards the bilogically rich surface waters. Scary!

Then I read recently about a period 55 million years ago called the Paleocene/Eocene Thermal Maximum (PETM). The Earth was around 5-8 degrees warmer then than now and then something triggered a  huge release of Methane or CO2 from the bottom of the ocean. Temperatures rose a further 5 degrees or so and an 'acidification event' happened on the sea floor. It is still visible in the geology of the sedimentary rocks.

I just can't understand why some people can deny that the warming is even possible! Why not, its happened before?

2011-09-26 14:19:01


The past tells us much about what our future holds in store for us. In the past, when the Earth was warmer than it is now, sea levels were metres higher than current levels. So just on the sea level front alone, we can expect severe impacts on the vast majority of the human population living on coastlines. The past also describes these concerning feedback events, where warmer temperatures lead to further release of greenhouse gases. We're already seeing this start to happen in the Arctic, with methane bubbling from the permafrost and methane clathrates. The past paints a vivid picture of our future and it's a picture of great concern.

2011-09-26 14:46:22Que sera
Daniel Bailey
Daniel Bailey

1.  Increasing the level of a greenhouse gas in a planet’s atmosphere, all else being equal, will raise that planet’s surface temperature.

2.  CO2 is a greenhouse gas.

3.  CO2 is rising.

4.  Therefore (given 1-3 above) the Earth should be warming.

5.  From multiple converging lines of evidence, we know the Earth is warming.

6.  The warming is moving in close correlation with the carbon dioxide.

7.  The new CO2 (as shown by its isotopic signature) is mainly from burning fossil fuels.

8.  Therefore the global warming currently occurring is anthropogenic (caused by mankind).


Not exactly rocket science.

2011-09-26 14:47:11Done and dusted
John Cook


That's 10 comments for this thread, thanks all!