January 2020 was the 6th warmest on record in the UK, with a mean temperature 2C higher than the 1981-2010 average. Early in February it was announced that Antartica had recorded the highest temperature ever recorded there of 18.3C, beating the previous record of 17.5C in March 2015. The atmospheric concentration of CO2 in January 2020 was measured to be 413 ppm following the trend that has seen the atmospheric CO2 concentration increase more than 10% from just the year 2000. That the polar regions would warm faster than other parts of the planet had long been a prediction of global warming based on increased CO2 emissions. Nonetheless, to see the figures reported quite so starkly was startling.
Each month brings new headlines and more concerns about whether we are responding fast enough to limit global warming to 1.5 or 2C. And yet, the greenhouse effect was proposed back in 1824; the idea that carbon dioxide (and water vapour) were greenhouse gases suggested during the 1850s (1,2) and it was back in 1895 that Arrhenius predicted that doubling the atmospheric levels of CO2 (relative to 1890s levels) would result in a global temperature increase of 5-8C.
So given that it is such an established theory, why are we still arguing about it? And, more importantly perhaps, what has this to do with coffee?
It is, in many ways, an ideal connection for the theme for one of the Coffee & Science evenings that we’ve been holding at Amoret Coffee in Notting Hill. And so it was that a group of us got together over coffee to discuss the greenhouse effect and its links to coffee.
The first coffee-greenhouse connection is in the condensation. When you make a pour over, or even if you pour your coffee into a cold mug, you will notice the condensation forming on the colder glass (or ceramic) surfaces as the steam evaporates. We know that the droplets form because the temperature of the surface is below that at which water vapour will re-condense into liquid. Technically, this temperature is known as the dew point. And it is partly to dew that we owe our understanding of the greenhouse effect.
Back in 1814, William Charles Wells made a series of detailed observations about how, where and when dew formed. He was able to show that more dew formed on clear (or not terribly cloudy) nights and on surfaces that were exposed to the sky; they were space facing. Which brings us to a second coffee connection: just as your coffee cup warms you by radiating its heat (in the infra red) to your hands, so all objects with heat radiate their energy out. Wells realised that this meant that space was cold because, just as a coffee cup if it is not being heated and not surrounded by reflecting material (think about the inside of a thermos flask) will radiate its heat and get cold* so the surfaces of the earth, if there is no energy coming in from space and no surfaces above them to reflect their heat back at them, will also get cold.
If space is cold, you can calculate what the temperature of the Earth should be if the energy it is losing is balanced by the energy it gains from the Sun and when you do this, it turns out that the mean temperature of the Earth should be -18C or about 30C lower than that observed**.
This leads to the idea that there is a natural greenhouse effect whereby gases in the Earth’s atmosphere form a layer which lets through a large amount of the energy from the Sun but lets a lot less energy escape back through it from the Earth (owing to the lower frequency of the radiation being emitted by the Earth compared with that coming in from the Sun). This ‘natural’ greenhouse effect results in a warming of the Earth to a delicate balance and to the temperatures that we experience on Earth***. Fairly clearly, if this delicate balance is disturbed by adding extra greenhouse gases to the atmosphere it will lead to a warming effect (as Arrhenius predicted back in 1895), the question is how much and how fast?
We were very fortunate to be joined for the evening by Dr Robin Lamboll of the Grantham Institute of Imperial College London. Robin explained the latest science and understanding of the effects of climate change and of adding increased CO2 into the atmosphere. Particularly highlighting how an increase in CO2 leads to an increase in water vapour (owing to the initial temperature increase produced by the CO2) which is itself a greenhouse gas, and so the warming effects of a small amount of CO2 can be amplified by this mechanism.
At this point the conversation diverged away from coffee, not just because Robin is a tea drinker (!) but we moved onto the effects of sulphur dioxide in the atmosphere, local vs global temperature effects and the science of Eunice Newton Foote. We discussed what we know, and what we are just starting to understand, such as how what happens in one part of the world may lead to consequences in other parts of the world (weather wise). We also got to a discussion of albedo and the reflection of heat by ice via playing with a couple of infra red thermometers that we had to hand and the different ways that human eyes and shrimp eyes detect colour. How is this connected to climate change and coffee? I’m afraid that there is a connection but the path to it is a little circuitous for a write up. It’s the sort of thing that pops up when you have a number of people of different backgrounds all contributing to the discussion. This is what, from my point of view, makes these evenings so interesting (and on a personal level induces such pre-event nerves): the fact that the conversation can go in so many directions, with such different contributions from the attendees, that each evening takes on a different character, with a different set of connections and a new set of things to think about. I hope that others feel the same way!
Our next Coffee & Science evening is scheduled for March 2020. Please do sign up to the events list or keep an eye on the Facebook events page to learn details as they are announced. Thanks again to Dr Robin Lamboll for coming along in January. I look forward to seeing both familiar faces and some new people in March.
Bean Thinking’s Evenings of Coffee & Science @ Amoret Coffee are held approximately every 2 months from 5.30 until about 8pm at Amoret Coffee in Notting Hill. More details can be found here.
*Two caveats here: firstly the coffee will also get cold through convection and conduction, the connection is illustrative rather than precise – though were you to put your coffee into a vacuum it would cool via radiative cooling only. Secondly, Wells himself never made the coffee connection but instead considered the latest physics theories about heat.
**In “Introduction to Atmospheric Physics”, David Andrews, (2000)
***For details about how we can know what the temperatures have been over such a time period and the effects of other cyclical temperature variations on the climate, it’s worth reading “The Ice Chronicles” P Mayewski & F White, (2002)