In what Prof Judith Curry describes as “incomprehensible to me” and I would describe as “delusional”, the latest IPCC report (AR5) is likely to say the IPCC are MORE CERTAIN that humans caused the latter 20th century warming or as they put it in AR5:
It is “extremely likely that human influence on climate caused more than half of the increase in global average surface temperature from 1951-2010.”
This assertion by the IPCC is false. It is not backed by the consensus of the experts; it isn’t supported by statistics; it isn’t supported by logic, and it is patently obvious from the 20th century climate data.
Not supported by the consensus of experts
The evidential failure of climate models to forecast the recent pause in warming led last year to Prof Curry presenting to the Royal Society Meeting on Climate a presentation ‘Climate models: fit for what purpose?’ in which she concluded that they were not fit for purpose as a basis for government policy. No one disagreed at the time; no one disagree with the statement prominently positioned in the paper I sent to delegates afterwards. That at the meeting:
No one strongly objected when American Professor Judith Curry (2012) articulated what appears to be the new consensus amongst climate experts: that whilst short term weather/climate models are providing important life-saving information, longer term climate models still left a lot to be desired and were probably not presently fit for purpose as a tool for detailed policy making.
Just recently the Met Office finally admitted after numerous parliamentary questioned went unanswered that there is a proven statistical test that shows natural variation can explain all the changes we saw in the 20th century. As Bishop Hill put it so well:
It has been widely claimed that the increase in global temperatures since the late 1800s is too large to be reasonably attributed to natural random variation. Moreover, that claim is arguably the biggest reason for concern about global warming. The basis for the claim has recently been discussed in the UK Parliament. It turns out that the claim has no basis, and scientists at the Met Office have been trying to cover that up.
The Met Office use one statistical test and use this to state the warming must be man-made. But apparently, they chose to ignore another more appropriate statistical test and which does not support the IPCC statement (and then hid this fact), or as Bishop Hill puts it …
…the likelihood of the driftless model is about 1000 times that of the trending autoregressive model. Thus the model used by HM Government should be rejected, in favor of the driftless model. With the driftless model, however, the rise in temperatures since 1880 is not significant.
Climate models like those shown to the right, predict global temperature based on what is believed to be known about the climate. This is that “Warming of the climate system is unequivocal”**. Real data (as shown on the right in black) shows us there has been no warming recently. Using the simple illustrative equation that what me measure (DATA) is comprised of what we know and what we do not. Or what we can forecast and that which we cannot we can say that:-
DATA = KNOWN + UNKNOWN
Using the notation KNOWNmodels for what was believed to be known when the models were produced (as opposed to what is now “known”), because there has been no increase in global temperature when the models predicted an increase, we can say that the change in the measured DATA is zero. Therefore it follows that:-
UNKNOWNcurrent ~= KNOWNmodels
From this we can say that what is unknown or commonly termed “natural variation” is equal in scale to what was thought to be known which is the predicted man-made warming. From this we could say natural variation is similar in scale to the previously predicted level of man-made warming. However, because the temperature has been lower than forecast, the current predictions have also been scaled down. So now the “known” (or presumed known) scale of man-made influence is smaller than that previously predicted. This can be expressed as:
KNOWNcurrent < KNOWNmodels
Combing this with the previous equation we come to the conclusion that
KNOWNcurrent <~ UNKNOWNcurrent
In other words, because there has been no warming when warming was predicted, we can confidently say that: it is likely that man-made warming is smaller than natural variation.
20th Century Climate Data
It is an undeniable conclusion that natural variation is likely greater than the “known” impact of man-made warming for the period of about 15 years where warming has been predicted and not occurred, however can we also conclude this for other periods? The answer is yes. CO2 warming in the latter 20th century carried on at pretty much the same pace or smaller due to lower emissions so any effect in the latter 20th century will be comparable or smaller. But is there any evidence to support the assertion that natural variation is present at the same scale?
The above graph using HADCRUT data shows that the warming from 1910-1940 before CO2 was measured rising, which is considered to be mainly natural variation, is exactly the same size and length as the warming from 1970-2000. So natural variation has always been known to be similar in scale to man-made warming. So, even if all the warming in the period after the global cooling scare were man-made it is not greater in scale than natural variation.
Because the statistics, the logic and plain common sense tells us that man-made warming is smaller than “natural variation” or the “unknowns” that caused the climate models to fail, we can confidently say:
It is unlikely that human influence on climate caused more than half of the increase in global average surface temperature from 1951-2010.
No rational person could support the previous IPCC’s report where they said it was “very likely” that the majority of warming is man-made but to increase this confidence in the face of the failed predictions and the statistical tests that say otherwise is delusional.
**Although the IPCC statement refers to previous warming, the Wikipedia global warming article, which was created by people with a close connection with the IPCC, makes it clear that this statement is intended to infer future warming is also unequivocal: “Warming of the climate system is unequivocal, and scientists are more than 90% certain that it is primarily caused by increasing concentrations of greenhouse gases produced by human activities such as the burning of fossil fuels and deforestation.”