The CO2 experiment you can do at home.


‘Why’ you are saying, would anyone need to demonstrate CO2’s tendency to trap heat? ‘This was discovered 100 years ago, and demonstrated with mercury thermometers!’.

Well because presidents and prime ministers and EPA chiefs and party leaders and communicators of all kinds say that this is not a thing. Of course, this experiment won’t change their minds, its only science after all, but it does head off that one argument – that the CO2 effect is mind-bogglingly complex.

Put some vinegar into a tall glass. Add some baking soda. As it froths up CO2 is formed. It is heavier than air and you can literally pour it from the glass. If you get it right, you can pour the invisible gas over a candle and extinguish it. That was the kind of thing kids did in the old-old days to learn about science.

You can demonstrate the greenhouse warming affect of CO2 in a similar way. By placing two vessels containing mostly-air in front of a powerful light source, and by giving one a much higher concentration of CO2 than the other, its possible to actually measure the temperature difference between the two vessels.

You can do this with normal thermometers stuck to the inside of the vessels but its much cooler to go digital and to have a log. Then you get to make a graph like this.


Its too small to see the times at the bottom but the increased in temperature in the CO2 jar began at 13:24 and dropped away at 14:36. That was the point where I turned the light source off. Note the steep drop off as there was suddenly much less to trap and both jars moved to room temperature (around 20C). The three bars on the upper part of the lines are 30, 35 and 40 degrees C. So the differential across one hour was between 5 and 7.5 degrees. The sensors read in farenheit so I converted it along the way.


The equipment to do this will cost you less than $20 NZ on TradeMe.

  • Arduino board (any one will do) – 7.99
  • DHT 11 temp sensor (2) – 6
  • 7 segment display (2) – 4

If you do a bit of electronics you’ll probably have these – if not they are an extra $7.

  • breadboard $5
  • jumper wires – $2

Other stuff you’ll need:

  • Two identical vessels (I used Agee jars but plastic bottles would be fine)
  • A light source that throws out some heat. I had a 150W worklight from Bunnings
  • A computer to set up the Arduino and also to record the logs if you want them.
  • Vinegar and baking soda (to make the CO2)

Also get something to seal the vessels. They shouldn’t be fully airtight since pressure differences affect the temperature. But sealed enough to stop all the CO2 escaping immediately. I used clingfilm and rubber bands.

I put equal parts vinegar in both jars and added baking soda to one. To make it fair, repeat the experienment with everything in the same place but swapping the roles of the jars – so the control jar becomes the CO2 jar and vice versa.


Here are the parts and the names for all the pins. The pins on the Arduino are pretty clearly marked.

Parts to make an Arduino CO2 experiment

Now here’s how to join them up. Connect the 5V pin on the Arduino to the long red bus on the breadboard. You’ll need to connect every pin marked VCC to that bus. (note on the breadboard in the picture the long bus is actually separated in the middle – you’ll see a couple of leads joining it up).

Connect the GND pin on the Arduino to the blue bus. Connect all the GND pins to that.

Now the DHT11s. They have a DATA pin. I’ve connected the one on the left to pin 20 on the arduino and the one on the right to pin 21.

Last is the digital readouts – the two TM1637s. On the left readout DIO goes to digital pin 6 and CLK goes to 7. For the right readout DIO and CLK are 3 and 2 respectively.

Note that you can use other pins provided you set the right numbers in the program below. Its pretty clearly marked in the code.

Preparing the arduino

You’ll need to install the Arduino IDE. Then install the libraries for the DHT11 and the TM1637.

Then create a new sketch in the Arduino IDE and insert this code into it:

#include "DHT.h"
#include <TM1637Display.h>

// Two DHT temperature sensors with 7 segment display and
// logging to the serial port. Suitable for the CO2
// greenhouse gas experiment.  Note the values are all
// in Farenheight.

// Module connection pins (Digital Pins)
#define CLK2 7
#define DIO2 6
#define CLK1 2
#define DIO1 3

TM1637Display display1(CLK1, DIO1);
TM1637Display display2(CLK2, DIO2);

#define DHTPIN1 20
#define DHTPIN2 21 
#define DHTTYPE DHT11


void setup() {
#ifndef ESP8266
  while (!Serial); // for Leonardo/Micro/Zero
  Serial.println("DHT1xx test!");


void loop() {

  float f = dht1.readTemperature(true);
  float f2 = dht2.readTemperature(true);

  if (isnan(f2) || isnan(f)) {
    Serial.println("Failed to read from DHT sensor!");

  display1.showNumberDecEx(ftoc(f),0x80 >> 1, true);
  display2.showNumberDecEx(ftoc(f2),0x80 >> 1, true);

  Serial.print("Temperature1: ");
  Serial.print(" Temperature2: ");
  Serial.println(" ");
int ftoc(float x)
  return x * 100;

Capturing the logs.

You can cut and paste from the Arduino IDE’s serial monitor but the Arduino had no idea of the time so here’s a trick to add it for linux users.

Install minicom and use it to capure a log file. You can do this by running it against the USB port the Arduino is using:

sudo minicom --device /dev/ttyUSB0 --baudrate 9600 --capturefile=minicom.cap

(Note you’ll need to see on the Arduino IDE whether you’re using the same USB port and baudrate)

Here’s a line to catch the minicom file and add times to it while its being created:

tail -f minicom.cap | perl -ane 'print scalar localtime . " $_"'

The output from that can be schlepped into excel fror graphing.

And finally

So wasn’t that fun. When you’re bored with that you can use the parts (with a few more – maybe another 10 bucks) to make a logging, standalone methane sensor.


‘Why’ you ask, ‘would anyone want one of those? Surely the hundreds of well sites in NZ are monitored closely using sophisticated gear since we all know that fugitive emissions are the curse that effectively make gas as bad (or worse than) the coal it is meant to transition us from?’

Yup. You’d think that. But for about $30(NZ) you can have a one of your own. This one will run on a battery and can log to an SD card – meaning you can set it up anywhere and look at the logs later.

This can measure methane levels down to 200ppm. I think this is probably enough to see when its milking time, given a shed full of cows tend to get a lot of belching in while they wait. Its also well below the recommended safe concentration for workers (1000ppm) so its all together something you’re likely to see in the wild,

From the Whack-a-mole trenches.


(NOTE: Look out for the next podcast episode in the next fortnight. Dr Terrence Loomis, author of Petroleum Development and Environmental Conflict in Aoteraoa New Zealand)

People tell me not to do it – argue with out-and-out climate skeptics. But no one else wants to talk about the subject so I wind up there. Don’t do it. Probably. Honestly, I don’t know – not talking about it is worse, and staying in your echo chamber is not great either. If we’re talking, we’re learning, I suppose.

Let me tell you what I learned this week.

They need a new name.

They call us ‘warmists’ now. Which seems like a reasonable title. We still call them ‘skeptics’, which sounds anti-science, or ‘deniers’, which makes our cause sound like a religion. I’ll suggest something for now – see if you like it. Its based on the stages of grief:

  1. denial
  2. anger
  3. bargaining
  4. depression
  5. acceptance

I’m going to name them by stage. This might sound a little patronising, but screw it, they’re wrong and it’s killing us.

I really like some of these guys.

Disagreements with stages one to three wind up turning into a trading of links to news sources. Winning in this battle is generally just a matter of staying in the ring. You don’t win, the other person typically runs out of points and goes off to do something else.

Yeah, I know. This is probably a pointless exercise. Almost as pointless as not talking about it.

Seeds of doubt can be cast in either direction. I never convinced an anti wind turbine campaigner that they were a Good Thing. But I made the point that the ‘noise’ argument is terrible and the environmental damage is not much better. This left him on some weird ground – that certain frequencies of sound not audible to the human ear were making people ill. There’s a hill to die on.

But hang in long enough and you find they are just people, and you are just sparring. The stakes may be immense and involve life and livelihood, but eventually you start hitting ‘like’ when they land something funny. And so do they. Congratulations. In this unbearably long game you are at least listening to each other.

They do matter. Even when they are clearly as mad as eels.

Seeds of doubt are all it takes. When Christopher (Lord) Monckton, a British toff with a BA in Classics, announced he had created cures for Graves disease, herpes, influenza, herpes and MS (also reducing the viral load of HIV) that was not enough for his claims about Global Warming to be dismissed. He toured this country to packed houses and people still quote him. I was referred to one of his ‘papers’ this week in an argument. He is still a thing.

To that note, people remember being told by their leaders that warming is hoax for decades. Even if those leaders have changed their minds, their original statement still applies. They simply don’t come out to the public and say ‘I was wrong, and this is really important’.

I like the people I spar with, to be fair, but there is a special place in hell for people who were trusted to know about these things and took too long to listen, then never came out about switching. The fact that many of them are still on podiums finding ways to capitalise on this crisis makes me question our viability as a species.

A scientist, when not doing science, is simply another person with an opinion.

The scientific method, from Collins:

British: a method of investigation in which a problem is first identified and observations, experiments, or other relevant data are then used to construct or test hypotheses that purport to solve it

American: a method of research in which a hypothesis is tested by means of a carefully documented control experiment that can be repeated by any other researcher

If someone with a background in science is telling you something that was not created using this method, then its just an opinion. These things are great when you want to decide what to learn. After that, do some science or save yourself some time and check out the science that is already there.

That’s pretty much what we do anytime we engage in any activities that the other mammals aren’t into. Actually, we use science to obtain food and hunt for a mate so maybe we’re just talking about breathing, digesting food and walking around at this point.

Some scientists NOT doing science when telling us about climate change include David Dilley and Doug Edmeades. There are many more but they came up this week. Telltale signs of ‘not doing science’ include:

  • Providing arguments based on too few observations
  • Not working the steps that turn observations into a hypothesis
  • Not submitting this work to other scientists for review

David Dilly noted three spikes in ocean temperature, 8 years apart, in the last 20 years, and turned that into a statement that dismissed pretty much all of other the science on the subject. To a scientist this is clearly absurd, but the man in the tweet buys it, because we respond to official titles and the presence of patterns.

Fictional characters can be scientists too.

One item making the rounds is the OISM petition project. This petition purports to be the opinions of over 31,000 scientists refuting the consensus on global warming. This is held up in response to the claim that over 97% of climate scientists agree that global warming is caused by humans. The thing was, this is an online petition where anyone claiming to be a scientist could sign and it didn’t matter what kind of scientist they claimed to be. Only 39 claimed to be climate scientists.

To make the point that this petition was not legitimate some signatories used names of Star Wars characters and one signed up as Spice Girl Geri Halliwell. Attempts to locate and identify these and most of the contributors to this survey were fruitless.

Laugh all you like, but people confidently cite this petition as proof of warmist propaganda. Its sticks and it worked.

Still it matters.

So. Many. Moles. Still, they clearly do matter, since people really think the clearly insane. We should explore for more oil, gas is a transition fuel, fracking is safe, cows can be reverse engineered, industries can be trusted to regulate themselves, the temperatures will fall again, there’s more ice and polar bears reckon its a good time get into real estate.

Don’t think you’ll look back on changing your lightbulbs or recycling as appropriate responses.

Pick up a hammer. Better still, find something that makes more difference. Clearly we are all thrashing around at this point and our efforts seem hopeless. But start with the effort. You might get lucky.

Quick video on methane


I’ll be recording an episode with Dr Terrence Loomis this month. This conversation will talk about the Oil and Gas exploration decision, the MBIE briefing advising the government to continue exploration, and the popular, but flawed notion than gas could serve as a transition fuel.

In the meantime the discussions about methane have recommenced. I recorded this short video explaining why methane from livestock is important and how it fits into the overall picture. Apologies for the audio on this – I expected to re-work it but ran out of time. If you like the format and think I should do more (and better!) videos like this please let me know. This really was a first attempt at the format. I could imagine other pieces talking about the history of carbon and the evolutionary process.