Excerpted with permission from “Facing up to Climate Reality: Introduction to the Project” by Brian Heatley and Rupert Read of Green House. First published in 2017, prior to the 2018 IPCC 1.5°C special report
The original title was “Dangerous Climate Change Is Now Inevitable,” because the piece doesn’t consider a scenario with activists forcing a rapid drop to zero carbon emissions. If we think and act outside of the box, we can achieve a path like that shown below in purple.
Our first assumption will be that dangerous climate change involving a temperature rise of at least 4°C by 2100 is now inevitable, despite the Paris Agreement and talk of 2°C. The purpose of this section is to persuade you of that.
It is not just the election of a climate change denier to the US Presidency that persuades us of this. Quite independent of Trump, and the way that other big emitters like the Chinese react to a potential US-prompted free for all, or whether the UK post Brexit will abide by EU targets, the Climate Agreement signed in Paris at the end of 2015 would not anyway have saved the world.
The headlines said that at Paris the world’s nations had agreed to limit climate change to 2°C, and even recorded an aspiration to keep it within 1.5°C. 1.5°C is plainly impossible; global average temperatures are now already 1°C above pre-industrial levels, and further warming to 1.5°C is now very likely indeed even if, per impossibile, no further greenhouse gases were emitted.1
But Paris will not contain the rise to 2°C, even if President Trump were to turn out to be a fervent environmentalist. To see this we have to see what the substance of the Paris Agreement actually was. Paris amounts to a series of unilateral ‘Intended Nationally Determined Contributions’ (INDCs) by individual countries. The EU countries (including the UK) for example have promised collectively a 40% reduction in domestic green house gas emissions by 2030. China says that its emissions will peak in 2030 at the latest, and that it will lower the carbon intensity of GDP by 60 - 65% below 2005 levels by 2030. The US has undertaken to reduce net green house gas emissions by 26-28% below 2005 levels in 2025. And so on. In total 185 countries covering around 94% of world emissions made such promises.
The small effect of Paris can be seen in the graph below. The blue line on the left shows what has happened up until 2010. The short red line from 2010 to 2030 shows what was expected to happen without Paris. The still rising green line shows what is expected if Paris were fully implemented. No, it’s not very different.
Historical and projected world greenhouse gas emissions 1950-2100
To see that the 2°C target is now impossible, we can use the IPCC’s estimate that to stay within 2°C no more than 1000 gigatonnes of CO2 equivalent could be emitted after 2010 (IPCC 2014, 10). We now add to that stock at a rate of about 50 gigatonnes a year (see graph). Even with the Paris pledges we will go on emitting over 50 gigatonnes a year for the next 20 years, or a total of 50 times 20 which equals 1000 gigatonnes. It defies everything we know about the longevity of energy infrastructure investments and how the economy works to suppose that emissions will just stop altogether in the 2040s, especially in growing economies. So 2°C must inevitably be substantially breached.
Even if in 2020 a radical programme of reduced emissions was started, and one that went far beyond the Paris Agreement, it would need to achieve zero emissions by 2040 to stay within the 2 ° C limit (the purple line on the graph). This is because by 2020 there will have been a further 10 years of emissions after 2010 at 50 gigatonnes per year making 500 gigatonnes. So after 2020 there are only 500 gigatones in total left (1000 - 500 = 500 gigatonnes). If we were to reduce to 0 emissions by 2040, we’d have 20 years with average emissions of 25 gigatonnes (because we start at 50 gigatonnes a year in 2020, and reduce to 0 in 2040). Then 20 years times 25 gigatonnes a year equals this 500 gigatonnes. Zero emissions by 2040 is simply not going to happen.
So what will happen? Surely the very most optimistic assumption we are entitled to make based on current political agreements and actions across the world is that emissions will continue to rise after 2030, hopefully leveling off later in the century though this is more hope than experience to say the least. This is broadly represented by the orange curve on the graph, which is associated with a 3-4°C rise. This is endorsed by a recent (November 2016) UN Environment Programme report which estimates that we are actually on track for global warming of up to 3.4°C on the basis of the Paris Agreement being implemented (UNEP 2016, pg xi) which one of the authors of this report predicted as the Paris Agreement was reached in late 2015. More realistically, we might instead expect the future simply to reflect the past, and follow the top light blue line, which is the IPCC’s ‘Business as Usual’ case, where the temperature rise is in the range 4-5°C.
So we must assume that the level of global temperature rise associated with carrying on as we are with emissions limited to broadly current levels—at the very least a 3 - 4°C rise by 2100, and more likely a 4 - 5°C—will now happen. This estimate is strongly biased on the side of optimism: