It's correct to have included this, but the message here seems less confident than that conveyed by the headline and opening sentence.

Actually the estimates of Equilibrium Climate Sensitivity (ECS) have long been around 1.5C - 4.5C, with higher values still thought possible. The IPCC 5th Assessment Report judged that there was up to a 10% chance of ECS being greater than 6C, and the likelihood of an ECS of 5C was assessed as less than 33% but more than 10%.

It's not clear what this statement is based on, as no source is given. Although several CMIP6 models produce an ECS above the upper end of the range of the CMIP5 models, this range was 1.2C - 4.7C so it is not clear where the description of a shift from 3C to 5C comes from.

This statement is not correct. Equilibrium Climate Sensitivity (ECS) has always been quite uncertain, and the high values in the new models are within the range previously thought possible, although relatively unlikely. A value of around 5C in some of the CMIP6 models is outside the "likely range" of ECS assessed in the IPCC 5th Assessment Report (AR5), but it is still not in the AR5 "very unlikely" range of above 6C. The recent studies cited in this report conclude that the high ECS values cannot be ruled out by the methods used in those studies, but they do not conclude that high ECS is more likely than previously believed.

This appears to be based on the view of a scientist who was not involved in developing the new models. A quote later in the article shows that a scientist with a leading role in the latest models is much more cautious and said it needs more research before conclusions can be drawn.

It's correct to have included this statement from a leading authority on the new models, but the headline and opening sentence of the article do not reflect the caution given here.

This is somewhat unclear phrasing from the report. Although studies have shown it is possible that the threshold for the Greenland Ice Sheet tipping point may be lower than 2C global warming (relative to pre-industrial), there is not currently a scientific consensus that this is where the threshold is. It seems to authors' scenario is that scientists living in 2050 have reached the consensus that the tipping point has been passed by that time, but that's different - again it's part of the scenario and does not support the "end of civilisation by 2050" headline.

The report ignores published work that has looked at the energy requirements for artificially-cooled environments in developing countries. The scenario here assumes those countries won't be able to afford it, but that doesn't mean they won't be able to in reality. Of course we shouldn't assume they would be able to afford it, but assigning "high likelihood" to either scenario as no real basis in published science.

So there is only a "high likelihood" in the scenario that the report's authors have constructed here. They do not say that their scenario itself is "highly likely" (in fact they say it is a "sketch") - so the headline of this article is not justified.

This is clearly from Mora et al (2017) although the report does not include a citation of the paper as the source of that statement. The way it is written here (and in the report) is misleading because it gives the impression that everyone dies in those conditions. That is not actually how Mora et al define "deadly heat" - they merely looked for heatwaves when somebody died (not everybody) and then used that as the definition of a "deadly" heatwave.

Again no baseline - presumably this must be 3C warming relative to pre-industrial. This is consistent with a high-end scenario of high forcing and strong feedbacks, but 3C between now and 2050 is not.

The baseline is not made clear, but I'm pretty sure that the original source cited in the report would have given this as warming relative to pre-industrial, not now. As it stands, the sentence gives the impression that we'd see 1.6C warming over the next decade, which is totally unrealistic and no peer-reviewed scientific study would claim that.

No, the report's authors have merely read (or possibly seen without actually reading) a few of the scariest papers they could find, misunderstood (or not read properly) at least one of them, and presented unjustified statements.

The "report" is not a peer-reviewed scientific paper. It's from some sort of "think tank" who can basically write what they like. The report itself misunderstands / misrepresents science, and does not provide traceable links to the science it is based on so it cannot easily be checked (athough someone familiar with the literature can work it out, and hence see where the report's conclusions are ramped-up from the original research).

The headline overstates the conclusions of the report (which is already overdoing things). The reports says it presents a scenario, and under that scenario and all the assumptions within it, the report claims that there is a "high likelihood of human civilization coming to and end" - but even then, the report itself does not give the end of civilisation within 30 years. The process supposedly leading ultimately to collapse begins around 2050 but takes a long time to take effect. Also the processes themselves are not well-grounded in science, as they over-interpret published work.

Actually studies suggest that we may already have postponed the next ice age by adding extra CO2 to the atmosphere which will take a long time to be removed by natural processes, and hence has committed the Earth to warmer temperatures than it would otherwise have had.

No it does not.

Because the amount of CO2 naturally present in the atmosphere depends on how much is being released or taken up by the oceans, land ecosystems and chemical reactions involved in rock weathering. These change naturally, but gradually, over thousands or millions of years. Human emissions of CO2 are merely adding an extra factor to the equation, but it is one which has a big effect over much short timescales (the last few decades).

The Earth's climate has always varied, even before humans began to influence it. Climate scientists have always been very clear about this. But human-caused emissions of COw2 and other greenhouse gases have now added a new cause of climate change in addition to the existing causes of natural climate variability.

No, it isn't. The fact that CO2 levels were higher 3 million years ago does not in any way contradict the fact that the current rise in CO2 is entirely human caused.

This may reflect his personal view, but I don't think this statement reflects the views of the meteorological community. Climate change has probably made the heatwave hotter than it would have been, but I've not seen any analysis suggesting that the additional impact of climate change on the heatwave is larger than would be expected from the 1C global warming that we've seen so far.

I agree with this cautionary note - the paper bases the 2C threshold on previous papers which themselves are reviews, and the paper says this is a "risk averse" approach

My reading of the paper is that it's the other way round - it asks whether it would stabilize at 2C or *could" gravitate towards a more extreme state. The paper is clear that this is about risk, not certainty, and that the proposed 2C threshold represents a "risk averse approach"

I think "not conclusive" is still too certain based on the actual level of confidence in the paper. I'd have said "tentative" would reflect the paper more accurately. eg. The paper uses the term "risk averse approach" for the proposed 2C threshold, and say "we cannot exclude the risk...". It also use caveated language such as "could" and "may" a lot, and talk of "probability ... difficult to quantify".

The paper says 0.09C not 0.9C

It would be fairer to say something like "commit Earth towards an eventual "hothouse" state"

"Move into" makes it sound sudden, but the paper suggests that although the feedbacks could be triggered soon and become self-perpetuating, they could take centuries to millennia to take full effect. Different words could have been used to make this clear.

The paper uses "could" not "will" (Table 1)

The paper uses "could" not "will" (Table 1)

The paper uses "could" not "will" (Table 1)

The paper uses "could" not "will" (Table 1)

The planet has survived these changes, but back then there were no humans around. Now we have many coastal cities, and populations of tens or even hundred of millions live within reach of sea level rises that have happened in previous warmer periods in Earth's history.

Nobody claims this, it is a strawman argument.

Because there are other drivers of change too, such as aerosol particles which have an overall cooling effect. There is also internal climate variability. Nevertheless, the long-term warming is attributable to increasing greenhouse gas concentrations.

Actually there is a relationship if you look on the appropriate timescales