Putting a number of catastrophe - the story of two degrees

There’s been a bit of fuss recently surrounding a new paper on how much more carbon we can blow before we’re really, really screwed.

Headlines varied from strong denier – we’re all fine and the scientists lied – to softer variations on this theme – hey guys, stop feeling guilty about that flight, things were going to be ok after all – with only a few really getting the point that this is only an update to current science which may, possibly, offer a tiny crack of sunshine within of what otherwise is still a pretty bleak view.

Let’s be very clear. All the authors are saying is that they now think that it is not geophysically impossible that we might manage to only heat the earth by one and a half degrees. There is still a massive gap between something being ‘not geophysically impossible’ and it becoming a political, economic, social and cultural inevitability (a massive gap, it should be said, we aren’t filling very quickly).

It’s also important to remember that this figure of 1.5°C global warming isn’t exactly all happiness and unicorns. It’s just a figure various parties have settled on as a line we’d rather not cross. They’ve settled on it based on a load of science, but also some morals, some arguing, a fair bit of compromise and the odd bit of laziness and misunderstanding too.

The production of numbers like 1.5°C (or 350ppm, or the year 2020) are based in science – which itself is based on reading nature – but are also, perhaps inevitably, massively political. Numbers like these can offer an illusion of a weird sort of pure faciticity, a sense of truth beyond human meddling. But they are a long way from that, and we should be careful about endowing them with quasi-religious power. We need to remain attuned to the politics that helped build these numbers and bring them to our attention, along with other human actions which made these numbers, like just being a bit crap and lazy.

So here’s a bit of background on all this talk of 1.5°C to help us get a better sense of what it means.

To start off with, a small sketch of the scientific work that goes into this number. This 1.5°C number refers to the average temperature for the whole world, for the whole year, above what it was before we started pumping out all that extra carbon dioxide in the industrial revolution. By average, it’s the ‘mean average’ which means they added up all the numbers for the year and divided it by the amount of numbers they had. Although both temperatures and climate change impacts vary by place-to-place and time-to-time, this collective temperature check on the planet is a useful signpost, offering an iconic sign of where we’re going. 

You’ve probably seen Ed Hawkins’ gif showing warming over time (it featured in the Rio Olympics). If not, or in case you just want a reminder:


In case you’re curious where we are at the moment, it was a bit under one degree in 2016. It was the warmest on record.

What counts as ‘pre-industrial’ is an interesting question. Most research works from 1850-1900 as a baseline. But maybe that’s a bit too late in terms of when we really started pumping out all that carbon, plus it’s a bit messy because of some big volcanic eruptions around then. So some people argue we should be working from 1720-1800. But on the whole, if you see ‘pre-industrial’ in a global temperature context, it means end of the 19th century.

In terms of how we get this number, we can’t just stick a thermometer under the planet’s armpit and have a row over whether it’s well or enough to go to school. The truth is a pretty awe-inspiring mix of methods, with temperature stations on land, sea and in even in space. There are four major data sets. One in Japan, two in the USA and a fourth in the UK. When it comes to measurements on land, scientists tend not to physically stick thermometers in the ground either, but instead go for the air, usually a meter and a half above the ground in weather stations – so strictly speaking, when scientists say 'surface temperatures' they mean nearish-to-the-surface temperatures. When they measure the water, it usually goes in between 1mm and 20m deep, often over the side of a ship, or using buoys. Up in space, satellites use infrared and microwave data. When scientists make conclusions about the Earth’s temperature they draw on a mix of multiple sources to get the fullest picture possible. (If you want more on this topic, there’s a great Carbon Brief explainer, and a really useful blogpost from Imperial College).

And this C thing? It’s Celsius, which you probably know about from the weather (unless you are American) or school. It’s a system first proposed in 1742 by a Swedish scientist named Anders Celsius. His scale was built from the freezing and boiling points of water – no degrees at one end, and one hundred at the other. Anything colder than the freezing point of water was minus something or other, and obviously it was easy to go above 100 degrees for things that were hotter. Celsius originally called it a centigrade scale, from the Latin for ‘one hundred steps’ and it’s handy for us humans because we like to count using our fingers (i.e. in tens) and we spend a lot of time playing with water. How we came to measure temperature in the ways we do is a story for another time though (read Hasok Chang if you’re interested) the point to remember is that like all ways of measuring temperature it’s made up, but it’s useful. It’s also worth keeping in mind that the numbers that might seem neat and significant to us – us humans with our ten fingers – like 1.5 or 100 or 2 are just numbers on a scale. Nature has its own games to play.

But to really get a sense of why 1.5°C is a big deal, we also need to understand its political history too.

One of the key things to come out of the 2015 Paris climate talks was an agreement to at least ‘pursue efforts’ to limit global temperature increases to 1.5°C above pre-industrial levels. Writing in Nature Climate Change in summer 2016, a group of scientists led by Daniel Mitchell at the Environmental Change Institute at the University of Oxford described this as one of the most momentous decisions of the decade (paywall free edition if you want to read it).

This was important because, up till then, people had mainly been throwing 2°C around as the big scary number we should work together to avoid.

And why 2°C?

I’d love to say it was because back at the end of the 20th century, some scientists – well funded to do the best, most comprehensive work – carefully calculated this figure as the safest possible limit we humans and our carbon emissions could push the planet’s climate to. They then collaborated closely with those most vulnerable to the impacts of climate change to give advice to politicians who made wise and caring decisions based on that. Then, by 2015, the science had been updated so, again, everyone sagely changed their minds and we upped ambition.

But sadly our approach climate policy didn’t work out like that.

Wind back the early 1990s. Things were hotting up in climate change, and not just in terms of the actual planet getting warmer (although that was a thing too).

The science was building, and politicians and advocacy groups were picking up the pace too. Thatcher had made her speech to the UN in 1989 Nasa’s James Hansen had been getting press for his testimony to the US Senate. And policy makers were, perhaps understandably, asking the question ‘what counts as really, really bad?’ What would count, numerically count, as a catastrophe?

It’s understandable that in order to build international agreements they wanted some simple, guiding numbers. Stuff to talk to voters and businesses and newspapers and each other about. A numbers or two which would offer the basis for target setting, the distribution of various funds and commitments.

Still, it’s arguably also a somewhat disingenuous question to ask, as they’re really kind of asking 'how long can I put this off for?' Plus, it’s not necessarily a fair question to ask scientists. For all that scientist can tell you about the ways in we are warming the planet and might in the future, as well as the sorts of impacts this might have, what counts as 'bad' is a subjective, moral point for the politicians and wider society to work out for themselves.

Researchers from the Stockholm Environment Institute did try to offer some sort of detail though, with a report published in 1990 on targets and indicators of climate change (full thing if you want to read it). This referred to two different targets - 1°C and 2°C. They recognised that even with a lot of speedy action we were likely to go beyond 1°C but at the same time 2°C degrees was a long way from safe. Sadly, too many seemed to take this 2°C line as some sort of speed limit to try to avoid (or just feel naughty if you passed) rather than the massive flashing 'toxic danger danger do not go anywhere near this' sign it was meant as.

If you want to scratch back a bit further, 2°C has some history in the 1970s with a couple of papers from Yale economist, William Nordhaus. He refers, almost in passing, to 2°C as a point where we’d have pushed the climate beyond the limits humans were familiar with. As David Titley argues, Nordhaus was thinking out loud about what what a reasonable limit for carbon emission might be, and clear that science alone shouldn't set this limit – it must account for both society’s values and available technologies. Nordhaus himself stressed how ‘deeply unsatisfactory’ his thought process was, and it’s perhaps rather painful to think that it ultimately became a cornerstone of international climate policy.

Back to the policy-chat. The 1992 Rio talks fudged things a bit, saying they didn’t want ‘dangerous’ climate change, but without opening a can of worms over what this thing they called dangerous actually looked like, precisely.

The EU wanted something more though, and in 1996, the European Council of environment ministers formally adopted two degrees as the line they didn’t want to cross. As Carbon Brief point out in their long read on the idea of the two degrees ‘speed limit’, the signatories to that statement included people who now sit at the forefront of international climate politics – the current chair of the UK’s Committee on Climate Change, John Gummer, and Germany’s Angela Merkel. 

As 2°C made its way from the EU to global climate policy, were three key (and conflicting) problems with this idea of two degrees. Firstly, for some, it seemed just way too ambitious. It meant dropping fossil fuels at a rate many would just not stand. Secondly, at the same time, it wasn’t nearly ambitious enough. Letting our planet warm by two degrees would put too many people in danger. Finally, it didn't really help policy makers work out what we need to do and communicate this action to the wider public (in contrast, a set of broader 'vital signs' might be more helpful).  

Roll on to the 21st century, and the Kyoto protocol was due an update. A joint editorial published by 56 global newspapers before the 2009 Copenhagen talks explicitly referred to two degrees as a way in which ‘the science is complex but the facts are clear.’

Except it was far from clear. It made for a good slogan to build momentum in the face of people who would rather keep burning oil than take action, but didn’t ignored the fact that for a lot of the world, two degrees was still very dangerous indeed.

At 2°C, parts of southwest Asia, including places with big populations like the Persian Gulf and Yemen, would be basically uninhabitable without pretty drastic air conditioning. Just that half a degree between 1.5°C and 2°C could half corn yields in parts of Africa, and mean total flooding of many coastal regions and islands. We pretty much loose the coral reefs if we go beyond 1.5°C too. (useful Fread Pearce feature if you want to read more).

And yet 2°C was still way too ambitious for a lot of people. The Copenhagen talks pretty much collapsed, and wasn’t until the following year, in Cancun, that the UN could agree to “hold the increase in global average temperature below 2°C above pre-industrial levels.”

As we moved towards the Paris talks in 2015, climate policy chat was increasingly suffused with the idea of 2°C. If there was doubt, it was more likely to be around whether 2°C was possible than whether it was desirable.

Indeed, the focus was so squarely on 2°C that when the UN negotiators in Paris emerged with a commitment not at least try to keep to 1.5°C there wasn’t even much research to help us work out how to do that. The UN asked the IPCC – an international body that assesses the state of scientific literature on climate change – to issue a special report on 1.5°C, to be published in October 2018. Work like that paper that caused all the fuss the other week is part of the work scientists are doing to find out more.

So, where does that leave us? Is 2°C safe? Depends where you’re standing but no, not really. Is 1.5°C safe? Again, depends where you’re standing, but it does look better. Should we be annoyed that the climate policy of the 1990s and 2000s has left us targets that were both way too ambitious and no where near ambitious enough? Yeah, I think so. Can we manage to keep to below 1.5°C warming? Theoretically, yes.