Deciphering the ‘SPM AR6 WG1’ code

I followed with great interest the launch of the sixth assessment report Working Group 1 (The Physical Science Basis) from the Intergovernmental Panel on Climate Change (IPCC) on August 9th. 

The main report is quite impressive (see earlier posts here, here, here, and here) but the press conference didn’t come across as being focused and well-prepared. In my opinion the press conference on 9 August 2021 didn’t do justice to the vast effort that went into it.

I was nevertheless pleased to see a great improvement from last time, which is that the full report (‘AR6’) was made available by the time of the launch of the summary for policy-makers (SPM), but I still have some issues with the way the SPM has been laid out. 

The problems with the SPM are similar those from the previous fifth assessment report which prompted me to write a post in 2013. Neither the present nor the previous SPM have much resemblance to either being a summary or being written for policy-makers. 

The new SPM covers 41 pages, and one could debate whether that can be called a ‘summary’. I think it would improve with cutting down on the amount of information, only keeping the most important points. 

Also, the summaries of the IPCC reports can seem a bit confusing. In addition to SPM, there is also a Technical Summary (150 pages long). Why? And who is supposed to read it? 

I think in hindsight that my concerns from 2013 to some extent were supported by the fact that the IPCC organised an Expert Meeting on Communication, Oslo, Norway, 9–10 February 2016. Some of recommendations from its Meeting Report  were:

Author  teams  should  include  or  be  supported  by  science  writers  (scientists,  or  journalists  with  a  science  background, who write professionally about science for non-specialist audiences), at least in the SPM team.

Authors should be trained in writing and communicating, including the use of clear language, as budgetary resources allow. A guidance paper on writing (e.g. short sentences, no jargon) should be established with the help of professionals.

Avoid  the  temptation  to  squeeze  too  much  information  into  graphics  that  are  difficult  to  understand, in an effort to comply with page limits.

Another clue indicating a shortcoming is if you look at the atmospheric CO₂-concentrations over time to see how much impact the IPCC reports have had on the real policy-makers in the world (Figure below). You should keep in mind that the CO₂ concentrations increase because some of us have worked hard to extract fossil resources from the ground. 

The data indicates that the emissions have kept increasing regardless of the scientific knowledge and our understanding. One question is whether that has been a result of a communication gap. 

One argument that has been made on Twitter is that the SPM is meant for decision-makers within climate-related bureaucracy. But I suspect that there is not much new information in the SPM for this group of professionals. Most of those that I have met tend to read the full assessment report. 

There is nevertheless a need to reach policy-makers who are unfamiliar with climate science. I wonder how many of this type of decision-makers actually read and understand the SPM. It’s a struggle to read, even for me.  

There are some easy tricks to improve a text. You can change the order of the sentences and words to improve the flow and make less complicated sentences. Fewer numbers and ranges cited in the text also help, if some are not as important than others. 

I have also learned from journalists that it’s a good idea to start with the most important information – that doesn’t change its contents. 

There is no need to keep all the cryptic citations and elaboration of the uncertainties since this information is already in the main report. After all, it’s supposed to be a summary for policy-makers and the main report contains all the details.

One suggestion is to get policy-makers who are not so familiar with global warming and man-made climate change to read the SPM and then ask them if they understand its main messages. Maybe give them a quiz to see how much they remember. 

Another question is how policy-makers should act on the information provided in the SPM. 

Since the SPM isn’t a brief summary written in layman terms, I’ve taken the liberty to try to write one based on the SPM below. I hope it conveys the most important messages of the SPM. 

A shorter summary for policy-makers in layman terms

There is no doubt that we have changed Earth’s climate through our activities on a broad range of aspects that includes consequences for the atmosphere, the oceans, snow, ice, Earth’s fauna and ecosystems. 

The cause of our changing climate is the increase in atmospheric greenhouse gas concentrations that we have released into the air. Carbon dioxide (CO₂) is the most important greenhouse gas that we have added to the atmosphere, however, some of it has been absorbed by land and oceans. 

The CO₂-concentrations have now reached an annual average of 410 ppm, but it used to be around 278 ppm in 1750. Our analysis indicates that the CO₂-concentrations are now at their highest in at least 800,000 years. There is a similar story for methane (CH₄), now measured to 1866 ppb and nitrous oxide (N₂O) 332 ppb. 

The changing climate means that you cannot base your decisions on what you have experienced in the past, but must take into account the scientific calculations for the future because these gases will stay in the atmosphere for a long time and their concentrations are quite likely to continue to increase. 

The global mean surface temperature has increased in jumps and spurts since 1850, and is now somewhere between 0.8°C to 1.3°C higher than pre-industrial times. The observed global warming is to the best of our knowledge happening at the fastest rate than any time in the last 2000 years. 

Our scientific calculations indicate that the greenhouse gases we have emitted so far are responsible for a global warming of somewhere between 1.0°C and 2.0°C since the industrial revolution, however, other types of pollution have had a moderating effect on that warming. In addition, ozone depletion higher up in the stratosphere has caused a cooling high up in the atmosphere. 

More rain is falling on Earth than before with a faster increase in the amount since the 1980s. This is likely an effect of man-made climate change. Mid-latitude storms have moved nearer the poles, and our scientific analyses have exposed a connection between man-made greenhouse gases and a poleward shift in the southern hemisphere jetstream in austral summer time. This displacement of the jetstream has consequences for high and low-pressure systems and subsequently rain and drought. Such changes may also have consequences for both agriculture, water management and wildfires, and it is likely to continue into the future. 

The world’s glaciers are melting because of man-made global warming, and the sea-ice area in the Arctic is shrinking fast: a 40% reduction during the September month since 1979 when the first satellite observations became available. Our scientific analysis also suggests that the annual average Arctic sea ice area has now reached its lowest level since at least 1850. Similarly, the snow cover is dwindling and our emissions of greenhouse gases can be linked to the melting of the surface of the Greenland ice sheet over the past two decades. Perhaps the Antarctic Ice Sheet also loses ice due to man-made global warming.   

Climate scientists are convinced that the world oceans have warmed down to a depth of 700 m since the 1970s because of our past emissions of greenhouse gases. CO₂ also has an additional effect: it makes the oceans more acidic when dissolved in seawater. Furthermore, the oceans are being depleted of oxygen (known as ‘hypoxia’), which also is thought to be related to man-made global warming. These changes in the oceans is bad news for marine ecosystems.

The global mean sea level has increased by 20 cm from 1901 to 2018, and the rate of increase has accelerated and is now about 3.7 mm increase every year. This increase can be explained by man-made global warming, where increased temperature makes seawater increase its volume and melting from land-based ice provides an additional contribution. A thermal expansion explained 50% of sea level rise during 1971–2018, while ice loss from glaciers contributed 22%, ice sheets 20% and changes in land water storage 8%. This means more coastal erosion, increases the risk of coastal inundation and makes storm surges a bigger threat for coastal settlements.

In addition to physical changes, scientists have also observed other changes in nature that provide further evidence of global warming. One example is a lengthening of the growing season by two days every decade in the northern hemisphere. 

The changes in Earth’s climate have happened everywhere on the globe and are unprecedented in human history. 

Man-made climate change disrupts our weather and changes the statistics of extreme weather events across the globe. This includes heatwaves, heavy precipitation, droughts, and tropical cyclones. The sixth assessment report from the IPCC provides stronger evidence that changes in such extremes can be attributed to our activities. Heatwaves and extremely hot days have become more frequent and intense, whereas cold extremes have become more rare. There are also marine heatwaves, regions of hot sea temperatures, and they have become twice as frequent since the 1980s, thanks to human influence. 

The monsoon rainfall amounts decreased between the 1950s and 1980s, partly due to aerosol pollution, but they increased after the 1980s because of the increased greenhouse effect. The monsoon rainfall amounts are affected by a tug of war between aerosols and greenhouse gases. 

The number of the strongest tropical cyclones has increased and they have moved further away from the equator. Perhaps there are long-term trends in all-category tropical cyclones, however, we are more certain that the heavy rainfall brought by them has increased due to a stronger greenhouse effect for which we are responsible.  

We have recorded more extreme events that consist of a more complicated nature. For instance, an increased frequency of concurrent heatwaves and droughts, fire weather, and flooding.

The sixth assessment report presents more accurate estimates than ever for the amount of global warming that we can expect if the concentrations of atmospheric CO₂ were to double, the so-called climate sensitivity. The current estimate is 3°C, with a likely range of 2.5°C to 4°C. We have also managed to shift Earth’s energy balance with approximately 2.72 Wm² over the period 1750-2019 because we have added extra greenhouse gases into Earth’s atmosphere. This shift has resulted in excessive heat stored in the oceans (91%), ice melt (3%), atmospheric warming (1%), and Earth’s surface warming (5%). 

Scientific calculations provide future outlooks indicating that the Earth’s global warming since pre-industrial times will exceed the thresholds of 1.5°C and 2°C unless we stop emitting more CO₂ and other greenhouse gases. Similar calculations estimate global warming between the periods 1850-1900 and 2081–2100 in the range of 1.0°C to 5.7°C, depending on our future greenhouse gas emissions. More emissions result in more warming. The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago. 

The Arctic will continue to warm faster than the rest of the globe, but the hottest days in mid-latitude and semi-arid regions are also likely to be subject to the highest increase. There will of course be a series of brief and random natural fluctuations on top of the predictable long-term trends that may result in even higher temperatures in some years. Our calculations also indicate more frequent and intense hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts if global warming proceeds. 

We have to expect a wide range of consequences from global warming and our computations reveal an increased proportion of intense tropical cyclones as well as reductions in Arctic sea ice, snow cover and permafrost. In addition, our climate models simulate more intense heavy rainfall that comes at greater frequency with additional global warming. 

Higher temperatures will amplify permafrost thawing, loss of seasonal snow cover, of land ice and of Arctic sea ice. The Arctic is likely to be practically sea ice free in the month of September at least once before 2050.

The sixth assessment report presents stronger evidence than ever that a continued global warming will intensify the global water cycle and the severity of the associated wet and dry conditions and more variable surface water flows. 

The annual precipitation amount may increase from the 1995-2014 levels with up to 13% by 2081-2100 averaged over global land areas. The mathematics of climate change gives more precipitation at high latitudes, over the equatorial Pacific and parts of the monsoon regions, and less precipitation over parts of the subtropics. Very wet regions become wetter and very dry regions drier, implying more floods and droughts. Rainfall associated with the El Niño–Southern Oscillation will also become more intense by the latter part of the century. 

The monsoon season is projected to have a delayed onset over North and South America and West Africa and likely a delayed retreat over West Africa.

The calculations presented in the assessment report indicate that mid-latitude storm tracks in the southern hemisphere will continue to shift southward, although the stratospheric ozone recovery counteracts may inhibit this shift for a while. The storm tracks over the North Pacific and associated precipitation may get displaced northward. Maybe this also will happen with the North Atlantic storm track. 

The ability of the oceans and land to take up some of the carbon that we emit to the atmosphere is estimated to diminish with global warming, which means that the increasing atmospheric concentrations may accelerate. The atmospheric concentrations of greenhouse gases are strongly influenced by how we deal with the emissions. The effect of changes to the ecosystems on the level of greenhouse gases is not fully accounted for.  

Many changes in our climate are irreversible for centuries to millennia. Earth’s climate has not quite caught up with all our emissions yet, and even if we stop emitting today, we will see further global warming at rates depending on the future emissions. Other long-lasting consequences include melting of glaciers and ice sheets, continued rise in the global sea-level (0.28-1.01 m by 2100), deep ocean acidification and maybe deoxygenation.  

It’s important to keep in mind that natural variations will continue in the future, and some locations may even experience a brief cooling period from time to time. These fluctuations can mask the long-term trends due to an increased greenhouse effect, especially on regional scales. 

We should not be surprised if at least one large explosive volcanic eruption takes place during the 21st century, based on paleoclimate and historical evidence. If this happens, it will briefly (lasting one to three years) lower the global mean temperature and alter the wind patterns. 

Really big and catastrophic consequences of global warming are unlikely but cannot be ruled out, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and a future warming substantially larger than the assessed very likely range of future warming. They should be part of risk assessment.

The sixth assessment report from the IPCC presents new and improved carbon budgets. We humans have emitted a total of about 2390 gigatons of CO₂ over the period 1850-2019. The remaining amount that we can emit depends on our ambitions to keep the global mean temperature below 1.5°C or 2.0°C. 

Perhaps we will manage to remove some of the atmospheric CO₂ in the future, which would make it easier to limit climate change. We can get a stable climate if the greenhouse gas concentrations are no longer changing, for instance by removing an equal amount to what we add, i.e. net zero emissions.

Needless to say, our scientific understanding has been reinforced further on all aspects of the climate system since the fifth IPCC assessment report that was published in 2013. Our knowledge is based on new evidence found in paleoclimate archives, new climate model simulations, new analyses, and of course new observations. In other words, multiple lines of evidence. There is a more robust understanding that we humans are having an effect on  a wider range of climate variables, including weather and climate extremes. All the evidence points in the same direction. Hence, these scientific conclusions are very credible.  

More details about climate change are provided in the main report. So why is this relevant for you? It’s important for you to be prepared for what may come and investigate how different types of weather and climatic changes may affect your livelihood. Since you are making decisions, you can influence your own future. You may need to adapt to a new climate and to do so, you need relevant and robust climate information specific for your needs. You need to use this information in a knowledgeable way. It’s equally important to make sure that you reduce your greenhouse gas emissions and your demand for energy.