Progress and date of last update

Highlights of assessments to date of global risks and related action plans

Progress update 9 August 2021

A paper by the Group was published on 21 June 2021

L. Mark W. Leggett & David A. Ball (2021) Empirical evidence for a global atmospheric temperature control system: physical structure, Tellus A: Dynamic Meteorology and Oceanography, 73:1, 1-24, DOI: 10.1080/16000870.2021.1926123


There is evidence that a natural control system influences global atmospheric surface temperature (Leggett and Ball 2020). The present paper sets up and tests a hypothesis concerning the physical makeup of the sequential elements of the control system and its outcomes. The final outcome that the control system influences is defined as global atmospheric surface temperature. The terms used for the control system element types in the hypothesis are, in sequence: leading element, controller and actuator. Actuators are hypothesised to affect, in turn, the final outcome – either directly, or via penultimate outcomes. The existence of the control system is evidenced by demonstration of statistically significant one-way Granger causality across each step of the hypothesised control system sequence. Evidence is presented that the leading element of the control system, represented by the Normalized Difference Vegetation Index, is the global biosphere. The biosphere as a control system has previously been referred to as Gaia (Lovelock and Margulis 1974). A fourth, second-derivative, term is found to enhance the Proportional, Integral and Derivative process terms of the control system shown in Leggett and Ball (2020). The main actuators of the control system found are shown to be wind speed and cloud cover. Cloud cover is shown to influence the final outcome, global surface temperature, directly. It and wind speed also influence the penultimate outcomes found, those of enhanced ocean heat uptake and enhanced outgoing longwave radiation. These together lead to control system output to the final outcome, global atmospheric temperature. Overall, evidence for the activity of the control system is shown to be present across many major physical dimensions of the Earth’s atmosphere.


There is a sense in which this paper completes – is the other half of – our presentation started with our last paper of our evidence that a natural control system influences atmospheric surface temperature at planet-wide scale. The paper does so by establishing various chains of Granger causality from a measure of vegetation greenness (NDVI) through various atmospheric processes to surface temperature.

Just as for the previous paper, from the global risk perspective, the paper provides information relevant to a fuller picture of the processes involved affecting the climate change risk. It fully supports the urgent need to move to a non-carbon, fully renewable global energy supply, particularly so when the still present global risk of peak fossil fuel is also considered.

Progress update 25 March 2021

A further paper by the Group was published on 24 February 2020:

L. Mark W. Leggett & David A. Ball (2020) Observational evidence that a feedback control system with proportional-integral-derivative characteristics is operating on atmospheric surface temperature at global scale, Tellus A: Dynamic Meteorology and Oceanography, 72:1, 1-14, DOI: 10.1080/16000870.2020.1717268



Here we provide statistically significant observational evidence that a feedback control system moderating atmospheric temperature is presently operating coherently at global scale. Further, this control system is of a sophisticated type, involving the corrective feedback not only of a linear error term but also its derivative and its integral. This makes it of the same type as the most widely used control system developed by humans, the proportional-integral-derivative (PID) control system.


This paper can be approached from a number of perspectives. From the global risk perspective, the paper provides information relevant to a fuller picture of the processes involved affecting the climate change risk. It fully supports the urgent need to move to a non-carbon, fully renewable global energy supply, particularly so when the still present global risk of peak fossil fuel is also considered.

Progress update 28 February 2018

The paper referred to in the 17 November 2017 update was published on 14 February 2018.  Relevant information is as follows:

Evidence that global evapotranspiration makes a substantial contribution to the global atmospheric temperature slowdown
Theoretical and Applied Climatology, (), 1-27

Our findings are summarised we hope clearly in the title and the Abstract which is as follows:


The difference between the time series trend for temperature expected from the increasing level of atmospheric CO2 and that for the (more slowly rising) observed temperature has been termed the global surface temperature slowdown. In this paper, we characterise the single time series made from the subtraction of these two time series as the ‘global surface temperature gap’. We also develop an analogous atmospheric CO2 gap series from the difference between the level of CO2 and first-difference CO2 (that is, the change in CO2 from one period to the next).

This paper provides three further pieces of evidence concerning the global surface temperature slowdown. First, we find that the present size of both the global surface temperature gap and the CO2 gap is unprecedented over a period starting at least as far back as the 1860s.

Second, ARDL and Granger causality analyses involving the global surface temperature gap against the major candidate physical drivers of the ocean heat sink and biosphere evapotranspiration are conducted. In each case where ocean heat data was available, it was significant in the models: however, evapotranspiration, or its argued surrogate precipitation, also remained significant in the models alongside ocean heat. In terms of relative scale, the standardised regression coefficient for evapotranspiration was repeatedly of the same order of magnitude as—typically as much as half that for—ocean heat. The foregoing is evidence that, alongside the ocean heat sink, evapotranspiration is also likely to be making a substantial contribution to the global atmospheric temperature outcome.

Third, there is evidence that both the ocean heat sink and the evapotranspiration process might be able to continue into the future to keep the temperature lower than the level-of-CO2 models would suggest. It is shown that this means there can be benefit in using the first-difference CO2 to temperature relationship shown in Leggett and Ball (Atmos Chem Phys 15(20):11571–11592, 2015) to forecast future global surface temperature.


Progress update 17 November 2017

The team has presently been advancing assessments on global risks in several specific areas.

On 16 November 2017 we submitted responses to referee comments on a new manuscript. This is about the physical factors behind the relationship between first-difference atmospheric CO2 (that is, the change in CO2 from one period to the next) and global surface temperature which we published in Atmospheric Chemistry and Physics in 2015

A progress report on the global wind and solar build is 90% complete and is currently on hold.

Climate change and peak fossil fuel

(last update November 2017)

Although there is a long way to go, the growth rate of wind and solar power over the last ten-year period is following a similar trajectory to that of other major infrastructure which  reached full or near full market penetration rapidly. If this rate of growth continues, peak fossil fuel will not matter because the diminishing fossil fuel would be replaced by adequate wind and solar energy; and no further carbon dioxide from fossil fuel burning will be emitted into the atmosphere after the mid 2020s, hence stabilising the climate at this time.

There are opportunities for global decision-makers in both the public and industry spheres to remove barriers and accelerate actions to foster the current wind and solar energy production trajectory being continued.

Near-Earth object risk

(assessment 17 November 2017)

Two types of object comprise the near-Earth object risk: asteroids and comets. Our reading of the literature suggests that of the two risks, the asteroid risk is now well understood.  Scientists have projected asteroid orbits into the future for the next 200 years,  showing, happily, that over that period no asteroid orbit is predicted to include a collision trajectory with  Earth.

But the comet risk is different from the asteroid risk. Our reading of the literature from a risk-analysis perspective seeking plausible worst-case scenarios suggests the following. There are two such worst-case scenarios for near-Earth objects involving planet Earth. Both involve comets.

The first is if Earth intersects with a stream of debris from a comet which has broken up. A mitigation response in this situation would require the capacity to intercept in the order of a hundred significant objects. The good news is that these objects would be traveling together in a stream. Hence it would appear that a smaller number than 100 intercepting spacecraft would be required, these spacecraft having the ability to target the full hundred objects and deflect them or pulverise them into objects small enough to be neutralised by impact with the Earth’s atmosphere.

In the second comet scenario the comet is large-scale and intact. Here a published strategy exists for the breaking up of the large comet by a nuclear explosive. As with the first scenario, the broken-up objects would  continue on their current trajectory and hence be fully available for further breakdown by further nuclear explosive impacts.

All the ingredients for the above strategies– the nuclear explosives and a high speed (VASIMR) rocket type — are presently available, or feasible at the scale required with further thoroughgoing workup. There would be considerable value in this workup being adequately funded starting with the next occurring budgetary round.

High-energy scientific experiments

(assessment 17 November 2017)

Several years ago a plausible worst-case scenario could be made that, based on aspects of particle physics theory, experiments of the European large hadron collider might produce novel to Earth objects which could greatly damage or destroy the Earth. This risk is made worse by the fact that while a major risk assessment was done, all those who participated in the risk assessment were physicists — many were employed by the operators of the large hadron collider — CERN – – all of whom had an interest in the outcome of the experiments.

This is a current case of the broader question of the governance of new experiments of this type. A best-practice risk assessment would require a multidisciplinary team — risk assessors, lawyers, ethicists and  representatives of the general public to as well as the professional specialists (in this case the physicists) – to  assess whether on balance an experiment should go ahead.

Since these concerns were raised, the Large Hadron Collider has run at record energies without immediate incident. (Global Risk Progress is in the process of consulting with both the risk and CERN communities to gain information for a quantitative assessment of what this means for the potential risks.) While there has been no immediate incident, very few of the other predictions of the  particle physics theories which generated the risk scenarios have come about either. If the risks did not come about because the theories suggesting them were wrong, while embarrassing for the scientists, it would be good news for planet Earth.