As warming approaches 1.5°C, a carbon budget for the Paris targets is delusionalJul 13, 2020
There’s a lot of talk about how much “carbon budget” (new emissions) are allowable to keep global heating to the Paris target of 1.5°C. The reality is that over the last year, global average warming was already close to 1.5°C, based on a true, pre-industrial baseline.
And the warming already in the system may well be enough to take the planet past 2°C, without any more emissions. The propositions pushed by governments, big business and many large climate movement NGOs that we have a “carbon budget” available for the Paris targets runs contrary to the evidence and suggests a world of politically convenient make-believe.
|Figure 1: Global warming July-to-June, illustrated here with a 1981-2010 baseline. Image by CarbonBrief.|
- According to CopernicusECMWF, globally, the twelve-month period from July 2019 to June 2020 was 0.65°C warmer than the 1981-2010 average (see chart above).
- Then 0.63°C should be added to these values to relate recent global temperatures to the pre-industrial level defined as a late 19th century baseline.
- So warming for the period July 2019-June 2020 is 1.28°C, compared to the late19th century, for which instrumental temperature records are available from 1850. This ties with the warmest year on record.
- But there was also warming from the start of the industrial revolution and the use of coal from the mid-eighteenth century, up to the end of the nineteenth century. That figure ranges up to 0.19°C, according to Importance of the pre-industrial baseline for likelihood of exceeding Paris goals.
- And new research published last year found that gaps with missing data in the observational temperature record are responsible for an underestimation of the global warming between 1881–1910 and 1986–2015 by 0.1°C.
- Adding up all those components takes the warming over the last year, from a true pre-industrial base, very close to the lower end of the 1.5-2°C Paris goal, whilst recognising there is some uncertainty about warming in the pre-1850 period.
As CopernicusECMWF note, “the value for this period is very close to that of the 12-month periods ending in May 2020 and September 2016, the two warmest such periods in this record. 2016 is the warmest calendar year on record, with a global temperature 0.63°C above that for 1981-2010. 2019 is the second warmest calendar year in this data record, with a temperature 0.59°C above average.”
Other datasets give slightly different results: “The spread in the global averages from various temperature datasets has been relatively large over the past three years. During this period, the twelve-month-average temperatures, relative to 1981-2010, presented here are higher than those from five other datasets, by between 0.03°C and 0.14°C, with median 0.06°C, for the year 2019. This is due partly to differences in the extent to which datasets represent the relatively warm conditions that have predominated over the Arctic and the seas around Antarctica.”
So what does this mean for advocacy around the Paris targets? As we have shown previously, warming of 1.5°C as a trend (rather than a one-year result) is just a decade away (see chart below), and a consequence of past emissions. And there is no carbon budget for 1.5°C. Nothing in the short-term bar geo-engineering — the use of sulfates to provide some temporary atmospheric cooling — will keep us under 1.5°C. But such approaches have not yet been demonstrated to be of net environmental or social benefit.
|Figure 2: Future co2 emission scenarios|
And 1.5°C by 2030 tallies with a paper published in 2017, ‘Trajectories toward the 1.5°C Paris target: Modulation by the Interdecadal Pacific Oscillation’, which found that in the absence of external cooling influences, such as volcanic eruptions, the midpoint of the spread of temperature projections exceeds the 1.5°C target before 2029, based on temperatures relative to 1850–1900.
The warming trend is 1.2°C at moment, based on 5-year running average, and 1.1C° based on 10-year running average (see figure below).
|Figure 3: Rise in global average temperature|
But if 2020 turns out to be a record year, and next year is hot as well, and then there is an El Nino, it may turn out that we are closer to 1.3°C trend already. It’s just that we don’t know, except in retrospect.
The warming rate appears to be around 0.3°C/decade at moment, but some including former NASA climate science chief James Hansen say the underlying trend may be ramping up towards 0.4°C:
La Nina minima probably provide a better estimate, and they provide more recent rates. As the figure (below) shows, the most recent two La Ninas imply a warming rate of 0.38°C per decade, at least double the longer term rate! Such acceleration is predicted by climate models for continued high fossil fuel emissions as a result of amplifying climate feedbacks and is a cause for concern. We expect global temperature rise in the next few months to confirm our analysis.
|Global warming acceleration becomes obvious by connecting global temperature at successive
La Nina minima. Credit: James Hansen.
If that is the case, history may show that that warming trend broke through the 1.5°C mark several years before 2030.
The role of aerosols in this calculus should not be underestimated, and in the question of committed warming.
Aerosols (including black-carbon soot, organic carbon, sulphates and nitrates and dust) are very short-lived particles in the atmosphere that have a cooling impact that lasts around a week. Most of these aerosols are anthropogenic, that is produced by human activity, and most of the anthropogenic aerosols are a byproduct of the extraction and burning of fossil fuels. Perhaps best known are the polluting sulphates and nitrates from coal-fired power stations, that combine with water molecules in the atmosphere to produce what is popularly known as “acid rain”.
The problem is our “Faustian bargain”: these aerosols are keeping the planet cooler than it would otherwise be, but are coming from burning fossil fuels that pour carbon dioxide into the atmosphere, heating the planet for centuries to come. The absolutely essential moves to eliminate fossil fuel emissions will also cut the cooling aerosol impact; the net effect will push the planet towards very dangerous warming conditions.
The question is how much warming are aerosols masking?
- A number of scientists have estimated the figure at around 0.5°C. Writing in the Huffington Post in late 2015, Prof. Michael E Mann noted: “While greenhouse warming would abate, the cessation of coal burning… would mean a disappearance of the reflective sulphate pollutants (aerosols) produced from the dirty burning of coal. These pollutants have a regional cooling effect that has offset a substantial fraction of greenhouse warming, particularly in the Northern Hemisphere. That cooling would soon disappear, adding about 0.5°C to the net warming… So evidently, we don’t have one-third of our total carbon budget left to expend, as implied by the IPCC analysis. We’ve already expended the vast majority of the budget for remaining under 2°C. And what about 1.5°C stabilization? We’re already overdrawn.”
- Prof. Stefan Rahmstorf agrees that “another half a degree of warming is already locked in – even without short-term fluctuations – taking us to the lower end of the 1.5-2°C limit agreed on by almost 200 nations last December in Paris.”
- Aerosol cooling probably reduced global warming “by about half over the past century”, says James Hansen, who estimates the temporary cooling “aerosol forcing -1.6 ± 0.3 watts per sq. m.”, which is around 1.2°C . That is, without the aerosols associated with burning fossil fuels, the planet would be more than a degree warmer, and well past 2°C.
- In a 2018 paper, “Climate Impacts From a Removal of Anthropogenic Aerosol Emissions”, Bjørn Samset and colleagues found that “removing aerosols induces a global mean surface heating of 0.5–1.1°C”, with a multi-model mean of 0.7°C. Samset says the vast majority of this net temperature change would be due to sulphate emissions from fossil fuel sources. This is because, in general terms, the other two forms of anthropogenic aerosols — black carbon and organic carbon, which have major contributions from biofuel and other biomass burning — cancel each other out, at roughly 0.1°C each, one cooling and one warming. In other words, going to zero emissions with carbon dioxide at ~420ppm would result in a warming of around 2°C at equilibrium, if the level of short-lived gases was constant.
- And Ramanathan and Feng in “On avoiding dangerous anthropogenic interference withthe climate system: Formidable challenges ahead” found that “The observed increase in the concentration of greenhouse gases (GHGs) since the pre-industrial era has most likely committed the world to a warming of 2.4°C (range 1.4°C to 4.3°C) above the pre-industrial surface temperatures. The committed warming is inferred from the most recent Intergovernmental Panel on Climate Change estimates of the greenhouse forcing and climate sensitivity. The estimated warming of 2.4°C is the equilibrium warming above pre-industrial temperatures that the world will observe even if GHG concentrations are held fixed at their 2005 concentration levels but without any other anthropogenic forcing such as the cooling effect of aerosols.”
And all this is without factoring the slow feedbacks, such as permafrost loss and weakening of other carbon stores. As Hansen notes, the lesson from our climate history is that if carbon dioxide is held at 400ppm (the current level is 417ppm), then “the eventual global temperature is expected to be about +3.5°C relative to pre-industrial temperature, including the effects of fast and slow feedbacks”. But that is another whole story for a future post.
From any sensible risk-management point of view — where special concern is given to the high-end and most devastating possibilities, not the middle-of-the road probabilities — there is no carbon budget left for the Paris targets.
Yet world-leading scientists tell us that “Even if the Paris Accord target of a 1.5°C to 2°C rise in temperature is met, we cannot exclude the risk that a cascade of feedbacks could push the Earth System irreversibly onto a ‘Hothouse Earth’ pathway.” ‘Hothouse Earth’ is a scenario in which system feedbacks and their mutual interaction could drive the Earth System climate to a point of no return, whereby further warming would become self-sustaining, without further human perturbations.
Let’s stop pretending that mainstream climate politics has the Paris goals as it real focus. It doesn’t, and suggesting that any more emissions at all from this day forward is compatible with Paris is bunkum. Supporting propositions of more emissions till 2030, 2040 or 2050 is talk in support of warming above 2°C and on the way to 3°C.
This week a study by Oxford Economics found that at 3°C of warming, GDP in India would falling 90% by 2100, and that is something government and business seems willing to contemplate even as they support continuing emissions for another 30 years.