A paper published last week in Nature Geoscience entitled “Emission budgets and pathways consistent with limiting warming to 1.5 °C” has set a few heads spinning. The primary thrust of it is that the amount of CO2 that can be emitted is perhaps bigger than previously thought if we are to still stick the goal of the Paris Agreement (keeping global temperature rise to under 1.5 degrees C).
That all sounds great. Unfortunately there are also several technical concerns, and so various Climate Scientists has been pointing out some of the flaws within the paper.
This is all par for the course is is what normally happens. The publication of a paper within a reputable science journal is part of a conversation and not simply a declaration of truth. It is how the wider scientific community interacts. Unfortunately, things have taken a rather weird right-hand turn. Some climate denying journalists have latched on to this paper and started distorting the content to advance their own very non-scientific agenda within the various media outlets that they scribble for. They are not engaging in the scientific conversation, but instead are touting a misrepresentation of this paper in the media as “evidence”.
First: What are the concerns within the paper itself?
Let’s briefly review the issues that have been identified within the paper.
Quote: “warming of about 0.9 °C from the mid-nineteenth century to the present decade”
The dataset they used to establish this was the HadCRUT global temperature data set, and that’s a bit problematic. It does not include data for the Arctic region. Since that is one of the fastest warming regions on the planet their analysis will not have been complete. The 0.9 C observation is also rather obviously not what has been measured or observed by other teams …
Headline claim from carbon budget paper that warming is 0.9ºC from pre-I is unsupported. Using globally complete estimates ~1.2ºC (in 2015) pic.twitter.com/B4iImGzeDE
— Gavin Schmidt (@ClimateOfGavin) September 20, 2017
It is also rather important to recognise that different groups use different baselines and different richer datasets, so they may indeed arrive at a different number.
What baseline should you use?
Human induced warming did not start in the mid 1800s, there is evidence that we were warming the planet prior to that date. So if you start with a baseline in 1850 then you will derive a number that others will quibble about because they use a different baseline and a different dataset.
CO2 does not go away – temperatures keep rising until they stabilise
When we emit CO2 into the atmosphere there is not an immediate warming, it takes time for the system to respond and stabilise.
We simply do not have the carbon budget that they claim because the method they used to calculate it is also flawed. If we stopped emitting CO2 right now we would still most probably be committed to a rise that takes us well over the 1.5 C target. The problem is that the calculation they used for a carbon budget is measured by the amount emitted between the baseline and the point at which we cross the 1.5 limit. After we cross that limit, the temperature rise will not stop, but will keep rising until it stabilises.
In summary, both approaches used by Millar compute budgets that do not actually keep global warming to 1.5 °C.
The Media Spin Cycle
Now let’s see how this paper has been abused by media outlets, and remember that these are non-scientific individuals that have a very specific climate denial agenda to promote for ideological reasons.
Ben Webster, the Environment Editor of The Times, has a reputation for distorted coverage of climate change, and is once again quite determined to maintain that reputation. He has latched on to this paper with a story that claims “We were wrong — worst effects of climate change can be avoided, say experts“. His source is a deliberately distorted misreading of this paper and so he writes as follows …
The world has warmed more slowly than had been forecast by computer models, which were “on the hot side” and overstated the impact of emissions, a new study has found.
That is simply not true at all.
Never willing to let itself be trumped by fake facts, the Daily Mail (and others) have also jumped in with an additional claim that the paper showed climate models had overestimated temperatures by ‘at least’ 0.3°C, and quoted one of the paper’s authors, Allen suggesting that this “a big deal,”
Claim of a substantial gap between model projections for global temperature & observations is not true (updated with 2017 estimate): pic.twitter.com/YHzzXtbhs9
— Gavin Schmidt (@ClimateOfGavin) September 20, 2017
Richard Miller and Myles Allen, the authors of the paper, have issued a formal statement that is highly critical of the media misrepresentations of their paper …
A number of media reports have asserted that our recent study in Nature Geoscience indicates that global temperatures are not rising as fast as predicted by the Intergovernmental Panel on Climate Change (IPCC), and hence that action to reduce greenhouse gas emissions is no longer urgent.
Both assertions are false.
Our results are entirely in line with the IPCC’s 2013 prediction that temperatures in the 2020s would be 0.9-1.3 degrees above pre-industrial (See figures 2c and 3a of our article which show the IPCC prediction, our projections, and temperatures of recent years).
What we have done is to update the implications for the amount of carbon dioxide we can still emit while expecting global temperatures to remain below the Paris Climate Agreement goal of 1.5 degrees. We find that, to likely meet the Paris goal, emission reductions would need to begin immediately and reach zero in less than 40 years’ time.
While that is not geophysically impossible, to suggest that this means that measures to reduce greenhouse gas emissions are now unnecessary is clearly false.
The Authors of the paper respond to misinterpretations of their 1.5C carbon budget paper on Carbon Brief in detail …
Our recent article, “Emission budgets and pathways consistent with limiting warming to 1.5C”, caused a bit of a media storm, so we would like to explain what the article did, and did not, do.
Choice of reference period: We selected 1861-1880 for consistency with AR5 carbon budget calculations (Figure SPM10 of WG1). This period was chosen in AR5 as the earliest period with reliable near-global temperature data, and in which there is no evidence of large volcanic activity.
…Our use of HadCRUT4 has been criticised because it is at the low end of estimates of warming in currently-available global temperature datasets. If the differences between these GMST datasets were attributable to random errors, this would be a valid objection, but they are not. They arise primarily because of different methodological conventions in the definition of GMST. HadCRUT4 defines GMST as the average of northern and southern hemisphere temperatures each calculated as a simple area-weighted average over regions with observations, using sea-surface temperatures (SSTs) over the oceans and surface air temperatures (SAT) over land. Other datasets that convert SSTs to SAT and/or use statistical models to estimate temperature estimates over regions without long-term observations (mainly Arctic, Antarctic and Africa) can give significantly higher estimates (by up to 0.2C) of warming to date, but would also have given higher levels of warming than were reported to the Structured Expert Dialogue, which confined itself to datasets assessed by AR5. The UNFCCC has not adopted a preferred definition of GMST, and until they do so, we feel it is justified to use a definition that approximates that which appears to have been used to provide the science background to the Paris negotiations.