6. Holes in IPCC climate science

base period compares with long-term trends and might affect the budget estimates’, the IPCC says. 73 As a specific temperature limit is approached, ‘relative uncertainties become larger’. 74

The remaining budget is affected both by uncertainties in past greenhouse gas emissions and estimates of the proportion of warming that is human-induced, the IPCC says. ‘As a result, only medium confidence can be assigned to the assessed remaining budget values for 1.5°C and 2°C and their uncertainty’. 75 Medium confidence? The whole edifice of the 1.5°C net zero emissions trajectory and timetable has been erected on a foundation in which the IPCC itself expresses only medium confidence.

Based on the modest confidence it has in its own data and analysis, the IPCC asserts with high confidence that net carbon dioxide emissions must decline by about 45% from the 2010 level of 49 GtCO 2 e by 2030, and reach net zero by around 2050. 76 The steep drop to 2030 is now steeper than implied by the IPCC. According to the UN Environment Programme, greenhouse gas emissions (including land-use change) grew at 1.3% a year in the decade to 2018, to 55.3GtCO 2 equivalent. 77 A 45% reduction from 2010 levels would require a reduction of 22GtCO 2 e, to 27GtCO 2 e. Emissions growth since then means the 22GtCO 2 e reduction is now a 28GtCO 2 e reduction and a 45% reduction has become a 51% reduction.

6. Holes in IPCC climate science ‘The science says…’ is a statement oft repeated by politicians and climate activists, as if climate scientists descend from Mount Sinai bearing tablets of stone inscribed with the commandments for our planetary future. As we’ve just seen, estimates of future warming and remaining carbon budgets are manufactured and involve the subjective choices and judgments of climate scientists. In a critical review of the 1.5 special report for the GWPF, Professor J Ray Bates, adjunct professor of meteorology in the Meteorology and Climate Centre at University College Dublin, raises additional criticisms over and above those made by Nic Lewis:

The IPCC does not discuss satellite-observed temperature trends, which show a warming trend of only 0.13°C per decade in the period 1979–2018, nor ask why they differ markedly from surface trends. A statistical analysis in which the prominent El Niño signal in the period 2000–16 is removed from the record finds the remaining warming trend is of the order of only 0.04°C per decade. 78

18 From 1900 to 1980, observed land and sea surface temperatures rose and fell at the same rate over multi-decadal periods. From 1980, a strong divergence appears, with land temperatures rising much faster than sea surface temperatures. Why? Though consistent with greenhouse-induced warming, the much weaker rise in sea-surface temperature does not unambiguously exceed the

Bates’s most powerful criticism is the practice of ‘tuning’ climate models so they reproduce past temperature trends and not being open about it.

Tunings that have enabled models to successfully reproduce the late 20th century warming have not enabled them to reproduce either the marked early 20th century warming or the recent slow rate of tropospheric warming. 80

Bates cites a 2017 paper, ‘The art and science of climate model tuning’, by Frédéric Hourdin and fourteen other climate modellers, which partially lifts the lid on this practice. Although tuning can be characterised as an objective process of estimation, ‘there is also subjectivity in climate model tuning’. 81 In theory, tuning should be taken into account in any evaluation, they write. In practice, it isn’t.

Why such lack of transparency? This may be because tuning is often seen as an unavoidable but dirty part of climate modelling, more engineering than science, an act of tinkering that does not merit recording in the scientific literature. There may also be some concern that explaining that models are tuned may strengthen the arguments of those claiming to question the validity of climate change projections. Tuning may be seen indeed as an unspeakable way to compensate for model errors. 82

Tuning strategies can also mislead climate scientists, the authors suggest.

Although tuning is an efficient way to reduce the distance between model and selected observations, it can also risk masking fundamental problems and the need for model improvements. 83

This danger of climate scientists deceiving themselves is especially acute concerning the values for the equilibrium climate sensitivity of carbon dioxide (ECS), which, in one form or another, drive temperature projections and define remaining carbon budgets for the 1.5 and 2 degrees specified in the Paris Agreement. Rather than use models to test possible values of ECS against observed temperature, the authors strongly imply models are tuned to confirm values that lie within a pre-ordained range. ‘One can imagine changing a parameter that is known to affect the sensitivity’, they write, ‘keeping both this parameter and the ECS in the anticipated acceptable range’. 84 In other words, climate modellers feel constrained to tune climate models in a way that avoids producing results that might challenge the scientific paradigm of potentially dangerous CO 2 -driven warming, a paradigm of fossil fuel emissions as the climate ‘control knob’ which Judith Curry calls a ‘simple and seductive idea’. As Curry notes:

this is a misleading oversimplification, since climate can shift naturally in unexpected ways. Apart from uncertainties in future emissions, we are still facing a factor of three or more [of] uncertainty in the sensitivity of the Earth’s temperature to increasing carbon dioxide in the atmosphere. 85