The new, massive climate change report by world’s leading scientists is out. For the first time, the Intergovernmental Panel on Climate Change is clearly telling governments that reducing heat-trapping emissions is not going to be enough. We have to get emissions to zero.
Every new barrel of oil, or ton of coal we burn is making the situation worse. In many ways, we are already in a danger zone, with the emissions we have already released to the atmosphere, so there really is no safe level of additional pollution anymore.
How fast should we get to zero then? Do we really have time until the end of the century? The short summary of the IPCC report introduces the concept of zero emissions, but is disturbingly vague when it comes to the timelines.
That’s why it’s important to look into the underlying science in the actual report for more details. Below are the relevant graphs and facts from the IPCC Fifth Assessment Report that can give more clarity on the timelines:
1. The starting point: below 2°C or below 1.5°C?
World governments have agreed to take enough action to limit warming to less than 2°C compared to pre-industrial levels. However, more than 100 vulnerable countries want the target to be strengthened to maximum 1.5°C, as for them, 2°C would already be very damaging. As their slogan says “1.5 to stay alive”.
The IPCC report proofs them right, as you can see below. 2°C would already imply high risks related to 2 out of 5 key risks defining dangerous climate change. Limiting warming to 1.5°C or below would be safer. (See the degrees on the right hand side, in the light grey thermometer.)
Source: IPCC Fifth Assessment Report, Synthesis report, page 104 of the longer report.
The choice of whether we aim below 2°C or below 1.5°C makes a big difference to the amount of emissions we can still release, and by when must we get to zero.
2. All greenhouse gases must head for zero by 2100 – or closer to 2050?
To keep warming below 2°C with higher than 66% likelihood we’d have to follow an emissions trajectory that is illustrated here below with the 430-480 ppm CO2-eq scenarios. (Follow the light blue line and the bar on the right). So basically, by 2100 we’d have to get all greenhouse gas emissions to about zero or even below.
However, the IPCC also says (page 15 of the SPM) that if we aimed for below 1.5°C warming, we’d probably have to get all greenhouse gas emissions to 70–95% below 2010 emissions already by 2050. Needless to say, zero would then also need to be reached way earlier too – closer to 2050 than to 2100.
3. Fossil fuel emissions will have to reach zero by 2070 or way before
Now, there’s a difference between all greenhouse gas emissions and the most important of them – carbon dioxide (CO2). It is the cumulative emissions of CO2 that largely determine global mean surface warming by the late 21st century and beyond.
As the graph below from the IPCC Synthesis Report shows, in average, CO2 emissions will have to get to zero by around 2070 (in scenarios that give about 66% likelihood of staying below 2°C).
Source: Figure SPM.5 of the AR5 Synthesis Report, Approved Summary for Policymakers
More than 90% of these CO2 emissions result from fossil fuels, cement and flaring. So it’s fossil fuel emissions, really, that need to get to zero by around 2070 or before in scenarios that aim below 2°C. Why before? See the next graph.
Source: IPCC AR5, Synthesis Report, Summary for Policymakers, Figure SPM.1 (d)
4. Later peak, higher certainty or no CO2 removal = earlier zero
The graph below helps to see why we should head for zero in fossil fuel emissions even before 2070. It’s from the IPCC AR5 WG1 Technical Summary.
It illustrates that it’s enough to get fossil fuel emissions to zero by 2070, if emissions peak by 2020; technologies that enable removal of CO2 from the atmosphere are available (and acceptable) by 2070; and we’re fine taking a risk that there’s a 1/3 risk that warming by 2100 could exceed 2°C.
Source: AR5. WG1. Figure TS.19
However, if it takes longer than 2020 for global fossil fuel emissions to start declining (now they haven’t even peaked yet), and/or we don’t want to count on negative emissions, and/or we want a higher certainty to keep below 2°C, and would rather stay as far below it as possible, then we need to get to zero well before 2070.
Also, if we want to leave room for “surprise factors”, like large releases of methane that could force to shrink our carbon emissions even faster, then we have another reason to aim for zero faster.
5. Electricity sector will have to get to zero even faster, by 2050 for <2°C
Electricity sector is easier and cheaper to decarbonise than other sectors like transport. Therefore, models typically assume faster cuts in electricity sector’s emissions. This applies to the models assessed by the IPCC too.
Here’s another figure from the IPCC summary released on Sunday. It shows you where CO2 and non-CO2 emissions will have to be around 2050 in different sectors, for these 430-480 ppm CO2-eq scenarios that aim at below 2°C. As you can see, in the electricity sector emissions need to get to about zero by 2050.
Source: IPCC AR5, Synthesis Report, SPM, figure SPM.14
6. Ocean acidification rates alone scream for zero CO2 asap
Let’s put the climate models aside for a while and simply look at CO2, and what it is doing to our seas. The ocean has absorbed about 30% of the emitted anthropogenic CO2, causing ocean acidification - which features heavily yin the IPCC's latest synthesis report.
As the World Meteorological Organisation recently warned, CO2 is now causing oceans to acidify at a rate that is likely the fastest in 300 million years, posing a serious threat to marine life. As a result, ocean scientists are urging governments to cut CO2 simply as low as possible, a fast as possible.
Alex Rogers, IPSO Scientific Director and Professor of Conservation Biology, University of Oxford has said: "The combination of acidification, warming and deoxygenation that we are seeing - the so-called 'deadly trio' is unprecedented in the carbon record. It poses a serious threat not just to the ocean but to the Earth system services it supports and there can be no stronger imperative for action by governments and others to reduce greenhouse gas emissions to the lowest possible levels in the shortest amount of time"
The IPCC has now opened an important debate on zero emissions that could be game-changing, as the negotiations under the United Nations Climate Convention (UNFCCC) have never before been about phasing out emissions, but about reducing and controlling them.
Now, the next step is to start defining by when should zero be reached globally? Do we head for 2°C, or 1.5°C, or even below? Should we first set a goal for zero CO2 emissions? By when?
In light of the realities of climate change - with key glaciers in the West Antarctic Ice Sheet already having reached a point of no return - I would urge a fossil fuel phase out and shift to renewable energy by 2050.