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Thoughts on AR6 – The Most Recent Report on Climate Change by the IPCC

Kit Webster

August 15, 2021


Irregularly, approximately every five years or so, the Intergovernmental Panel on Climate Change issues a report compiling current mainstream thought on the subject of climate change. The current report ( ) was released on August 9, 2021; the previous report was issued in 2013-2014; the first report was in 1990.

Although the IPCC has been caught manipulating outcomes toward the politically-correct results in the past, the current report should be considered relatively unbiased, except with regard to what I call “scenario abuse,” discussed below. There remains a bias toward presenting a bleak, and therefore newsworthy, picture, even though the assumptions on which the picture is painted are admitted to be unlikely.

Although not a climatologist, I have become a well-informed amateur through more than a decade of researching climate change – from Rush Limbaugh to Al Gore, relying heavily on scientific papers. I undertook this journey out of intellectual curiosity, and a frustration with the politically-correct bias in the media that was preventing rational consideration of all of the evidence.

My book, The Only Ten Things You Need to Know About Global Warming, which is the culmination of this research, is available for free at where you can either download it or read it online. In it, you will find that I “believe in” man-made global warming. However, the discussion around climate change is much more complicated than is contemplated in current public discussions by politicians, the media or celebrities.

In this paper, I would like to focus on several topics:

  • What is the current state of play, according to the IPCC?

  • What has changed in the IPCC’s views since 2014?

  • How is scenario abuse a problem?

  • How have my conclusions changed since I wrote my book, on which AR5 had a significant influence?

Following are my high-level responses:

  • The bottom line is that the report does not say much that is new, but it says what it says with increased confidence and what it re-states is often disturbing.

  • Media response is way overblown, bordering on hysteria. This report is a compilation of public data that has been out there for a while. Again, there is nothing new here.

  • Scenario abuse is a significant problem. Especially the media, but also writers of scientific papers and the IPCC, itself, emphasize low-probability, dire-outcome scenarios instead of presenting a balanced, or most-probable outlook.

  • There are no changes in my conclusions as expressed in my book.

Now to the details

But before discussing specifics, we need to discuss scenarios.

If you are going to forecast the future, you have to make assumptions about what the future will look like. In particular, if you are going to discuss climate change, you have to decide how many people there will be, how many automobiles, how much fossil fuel will be consumed, what government regulations regarding climate will look like, etc. The approach the IPCC takes is to define several alternative scenarios, from low carbon to high carbon, and then see what the modeling results are for each scenario.

Scenarios have changed over the decades, and the IPCC has given them different names. I will discuss scenarios in greater detail, below. For present purposes, think of them as defining different amounts of carbon emissions in the future as a result of different assumptions regarding human behavior and regulatory behavior in that future. In AR6, scenarios are labeled SSP followed by a number. In general, the greater the number the greater the amount of greenhouse gas emissions associated with that scenario, although the numbers basically have no intrinsic meaning.

In the past, the IPCC has, at times, associated its conclusions with some indication of the reliability or probability of that conclusion. Following is this year’s summary, however, with minor exceptions, its conclusions are not associated with any indication of reliability or probability.

Headline Statements from the Summary for Policymakers

9 August 2021 (subject to final copy-editing)


A. The Current State of the Climate

A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.

A.2 The scale of recent changes across the climate system as a whole and the present state of many aspects of the climate system are unprecedented over many centuries to many thousands of years.

A.3 Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report (AR5).

A.4 Improved knowledge of climate processes, paleoclimate evidence and the response of the climate system to increasing radiative forcing gives a best estimate of equilibrium climate sensitivity of 3°C, with a narrower range compared to AR5.

B. Possible Climate Futures

B.1 Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.

B.2 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.

B.3 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.

B.4 Under scenarios with increasing CO2 emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO2 in the atmosphere.

B.5 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.

C. Climate Information for Risk Assessment and Regional Adaptation

C.1 Natural drivers and internal variability will modulate human-caused changes, especially at regional scales and in the near term, with little effect on centennial global warming. These modulations are important to consider in planning for the full range of possible changes.

C.2 With further global warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Changes in several climatic impact-drivers would be more widespread at 2°C compared to 1.5°C global warming and even more widespread and/or pronounced for higher warming levels.

C.3 Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment.

D. Limiting Future Climate Change

D.1 From a physical science perspective, limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions. Strong, rapid and sustained reductions in CH4 emissions would also limit the warming effect resulting from declining aerosol pollution and would improve air quality.

D.2 Scenarios with low or very low greenhouse gas (GHG) emissions (SSP1-1.9 and SSP1- 2.6) lead within years to discernible effects on greenhouse gas and aerosol concentrations, and air quality, relative to high and very high GHG emissions scenarios (SSP3-7.0 or SSP5-8.5). Under these contrasting scenarios, discernible differences in trends of global surface temperature would begin to emerge from natural variability within around 20 years, and over longer time periods for many other climatic impact-drivers (high confidence).

The big change in these conclusions from those in previous reports is the use of the word, unequivocal, to describe humans’ contribution climate change. In general, over time, each successive report has used language indicating greater and greater confidence that humans are contributing to climate change. This is the first year that the relationship is expressed as being without doubt.

Otherwise, the conclusions have not changed much, although most are expressed with what appears to be greater confidence. This confidence appears to be the result of experiments and analyses carried out in the period between the two reports.

Some extracts from the report:

  • In the period between the two reports, the Earth’s atmosphere’s average temperature has warmed about 0.1⁰ C (0.18⁰ F), to an increase of 1.1⁰ C (2⁰ F) since before the industrial era.

  • (A little wonky, but important) The “equilibrium climate sensitivity”—the amount of warming to be expected as a result of a doubling of the carbon-dioxide level - has been computed with better precision. In AR5 the range was 1.5-4.5º C. Now it has been halved: AR6 puts the sensitivity at 2.5-4º C, with a best estimate of 3ºC. The good news is that this means there is less uncertainty in forecasts; the bad news is that there is still significant uncertainty.

  • The IPCC appears to be emphasizing the removal of carbon dioxide from the atmosphere as an approach to mitigate global warming.

  • Weather trends – (ht Roger J. Pielke Jr.) the IPCC uses the terms, detection and attribution. Detection means that something has changed without providing a reason for the change. Attribution means assigning a cause to that change. Following is a summary of conclusions from AR6, where attribution means, caused by man-made climate change.


  • Heat waves -


  • Heavy precipitation – frequency and intensity have increased at a global scale. This statement is characterized as being likely (> 66% certainty).

  • Droughts – four types: meteorological, hydrological, agricultural, ecological. “There is medium confidence that human-induced climate change has contributed to increasing trends in the probability or intensity of recent agricultural and ecological droughts.”

  • Tropical cyclones (hurricanes) - Low confidence in trends in tropical cyclone frequency or intensity.

  • Winter storms - Low confidence in trends in frequency and intensity.

  • Thunderstorms, tornadoes, hail, lightning – “There is medium confidence that the mean annual number of tornadoes in the United States has remained relatively constant.”

  • Extreme winds – “… the observed intensity of extreme winds is becoming less severe in the lower to mid-latitudes, while becoming more severe in the higher latitudes poleward of 60 degrees (low confidence).”

  • Fire weather – “There is medium confidence that weather conditions that promote wildfires (fire weather) have become more probable in southern Europe, northern Eurasia, the US, and Australia over the last century”

  • Tipping points – one area the IPCC has not emphasized in past reports is tipping points – abrupt events which move the climate rapidly into irreversible changes. While the current report also does not emphasize them, it does mention them more often than they have been mentioned in the past, and many of the mentions are low confidence. Tipping points that were mentioned include:


      Tropical forest dieback (low probability to occur in 21st century)
    • Boreal forest dieback (low probability to occur in 21st century)

    • Biogenic emissions from permafrost thaw (high confidence, discussed in my book) Large amounts of methane, a potent greenhouse gas, are trapped in permafrost in various areas of the Arctic. Should the permafrost melt, releasing the methane into the atmosphere, the amount of greenhouse gasses in the atmosphere would increase, accordingly. (high probability to occur in 21st century)

    • End of the currents, such as the Gulf Stream, in the Atlantic Ocean. (low probability to occur in the 21st century, however very likely they will weaken during that period)

    • Natural tipping points are discussed, including volcano eruptions.




Following are some charts that summarize the scenarios and the results from scenarios:

Carbon dioxide emissions assumed by the various scenarios:



Future temperature changes, above pre-industrial levels, resulting from various scenarios
















The IPCC does not assign likelihoods to scenarios. However, it does comment as follows:

“The likelihood of high emission scenarios such as RCP8.5 or SSP5-8.5 is considered low.”

This is also important because in AR5, RCP8.5 was considered by the IPCC as our most likely future. Now, it is judged as unlikely.

The most likely scenarios (my words, not theirs) would be RCP4.5, RCP6.0 and SSP2-4.5.

However, as detailed by scientist Roger J. Pielke Jr, whose writing I recommend:

Despite acknowledging the low likelihood of the most extreme scenarios RCP8.5 and SSP5-8.5, which were the dominant focus of the 2013 IPCC report, the extreme scenarios dominate the current report as well. This is obvious from the table below which shows the number of mentions of various scenarios in the new report.


In other words, in the current report, the IPCC references an unlikely scenario 42% of the time, and “most likely” scenarios 18% of the time.

How have my conclusions changed since I wrote my book on global warming?

The principal conclusions in my book are as follows:

1. Global warming has become politically correct, so that getting objective information is now almost impossible.

Global warming is like a religion - a topic on which there are some facts, but also huge areas in which there are no reliable facts - so that you have to take a leap of faith, draw your own conclusions and then ask others to join in your view of the world.

There is a "scientific consensus" (in the sense that a majority of scientists agree) that humans are contributing to global warming. However, there is absolutely no consensus on how much of a contribution there is, what the impact of any warming will be or what to do about it.

Any prediction of future climate that you see in the media is based on flawed models.

Climate is messy, highly variable, unpredictable, and only discernable over time frames of decades, as a minimum, and perhaps centuries

Most of our current conversation about global warming is irrelevant and misinformed

2. The greenhouse effect is a scientific fact.

A better statement of the problem is that there is a fear that humans may be sending the Earth's climate into territory which will cause rapid, significant disruptions to humans and to the Earth's plants and animals, significantly disturbing our status quo


3. Climate has changed dramatically in the past and will do so in the future – humans or no humans.

There has actually not been much global warming; we are, in terms of warming of the atmosphere and changes in sea level, pretty much where we should be in the cycle of ice ages; and what global warming there has been may have been has stalled for almost two decades.

The way to bet is that the Earth will get warmer and sea level will rise until the beginning of the next ice age, humans or no humans.

4. The amount of carbon dioxide in the atmosphere is increasing very rapidly.

5. Carbon dioxide emissions from our use of coal, oil and natural gas for fuel, heating and electricity are the bases of our prosperity and health.

6. No one knows how bad global warming will get – or whether it will be bad at all – however, there are potentially catastrophic outcomes.

Given mainstream assumptions about global warming, together with predictable energy generation in the short term, it is highly likely that it is too late to contain global warming within “safe” levels.

7, Renewable energy can help, but is unlikely to save the day.

8. Effectively stopping the global warming described by the IPCC (the United Nations body responsible for reporting a scientific consensus on global warming) could take the U.S. standard of living below that in the 19th century.

9. Technology has saved the day in the past; it may save us again.

In order to address the mainstream’s view of global warming, the technology cavalry must come to the rescue with several breakthroughs in climate management, CO2 management and alternative energy. Those technologies are not currently on the horizon.

10. There are things you can do to help – but, if mainstream thought is correct, whatever you do will not be enough.

There are no silver bullets in fighting global warming - this huge, complex problem will have to be attacked in multiple ways by all of humanity.

We are left praying for two things: that the models are wrong and global warming will not be all that bad; and that if the models are approximately correct, humans will achieve a technological miracle quickly enough to have a significant effect.


I was being a bit formal in my conclusions. Following are several, more-direct statements:

  • The Paris Accord is an aspirational document which is largely irrelevant except for political purposes (and one should not minimize political purposes). However, if its aspirations were actually defined and fully achieved, there would be minimal impact on global warming.

  • Absent catastrophe or the ability to actually remove CO2 from the atmosphere, the 1.5⁰ and 2⁰ goals for limiting the increase in atmospheric temperatures will almost certainly be impossible to achieve. Again, these are political instead of practical goals, and again, do not minimize the importance of political goals. From The Economist (which does not share my conclusion explicitly), “The budget associated with a 50:50 chance of staying below 1.5ºC allows just 500bn more tonnes of carbon dioxide to be emitted. That is about 15 years of industrial emissions at current rates (emissions from deforestation make things worse). For that to be all that is ever emitted would require the whole world, not just developed countries, to be at net-zero before 2050.”


So, how have my conclusions been changed from reading AR6?

Not much, I’m afraid.

  • Humans are contributing to global warming.

  • The cure to global warming will be very expensive and radically change economies and behavior.

  • Climate models are not sufficiently reliable to base public policy upon.

  • The media, politicians and celebrities are sensationalist and biased.

  • Renewable energy will be insufficient.

  • Catastrophic outcomes remain possible.


It is interesting that the IPCC is beginning to emphasize carbon dioxide removal from the atmosphere, which might indicate that its confidence that political solutions will be sufficiently effective is waning.


We are in the midst of an unplanned experiment within which we are addicted to the substance that may lead to our undoing.


AR6 basically tells us what we already knew, in stronger language and supported with additional experiments and data.

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